FIRST REVISION NAVAL SHIPS’ TECHNICAL MANUAL S9086 …

S9086-QN-STM-010/CH-475FIRST REVISION

NAVAL SHIPS’ TECHNICAL MANUAL

S9086-QN-STM-010CHAPTER 475

MAGNETIC SILENCING

DISTRIBUTION STATEMENT C: DISTRIBUTION AUTHORIZED TO U.S. GOVERNMENTAGENCIES AND THEIR CONTRACTORS; ADMINISTRATIVE/OPERATIONAL USE; 31 MARCH 1992. OTHERREQUESTS FOR THIS DOCUMENT WILL BE REFERRED TO THE NAVAL SEA SYSTEMS COMMAND(SEA-56Z22).

DESTRUCTION NOTICE: DESTROY BY ANY METHOD THAT WILL PREVENT DISCLOSURE OFCONTENTS OR RECONSTRUCTION OF THE DOCUMENT.

SUPERSEDES REVISION 0, CHANGE NOTICE 6, CHAPTER 475, DATED 15 JULY 1989

PUBLISHED BY DIRECTION OF COMMANDER, NAVAL SEA SYSTEMS COMMAND

31 MARCH 1992

A

S9086-QN-STM-010/CH-475

LIST OF EFFECTIVE PAGES

Page *Change Page *ChangeNo. No. No. No.

Title and A . . . . . . . . . . . . . . . . . . 0Flyleaf-1/(Flyleaf-2 blank) . . . . . . 0i through vii . . . . . . . . . . . . . . . . . 0viii (blank) . . . . . . . . . . . . . . . . . . 0ix . . . . . . . . . . . . . . . . . . . . . . . . . . 0x (blank) . . . . . . . . . . . . . . . . . . . . 0xi . . . . . . . . . . . . . . . . . . . . . . . . . . 0xii (blank) . . . . . . . . . . . . . . . . . . . 01-1 through 1-2. . . . . . . . . . . . . . . 02-1 through 2-7. . . . . . . . . . . . . . . 02-8 (blank) . . . . . . . . . . . . . . . . . . 0

3-1 through 3-18. . . . . . . . . . . . . . 04-1 through 4-134-14 (blank) . . . . . . . . . . . . . . . . . 05-1 . . . . . . . . . . . . . . . . . . . . . . . . . 05-2 (blank) . . . . . . . . . . . . . . . . . . 06-1 through 6-2. . . . . . . . . . . . . . . 07-1 through 7-12. . . . . . . . . . . . . . 08-1 through 8-18. . . . . . . . . . . . . . 0A-1 through A-2 . . . . . . . . . . . . . . 0Glossary-1 through Glossary-5 . . 0Glossary-6 (blank) . . . . . . . . . . . . 0

*Zero in this column indicates an original page.

S9086-QN-STM-010/CH-475

RECORD OF CHANGES CHAPTER 475ACN/FORMAL

*CHANGEACN NO.

DATEOF

CHANGE TITLE AND/OR BRIEF DESCRIPTION**ENTERED

BY

*When a formal change supersedes an ACN, draw a line through the ACN number**Only message or letter reference need be cited for ACNs

Flyleaf-1/(Flyleaf-2 blank)

S9086-QN-STM-010/CH-475

i

TABLE OF CONTENTS

CHAPTER 475

MAGNETIC SILENCING

Paragraph Page

SECTION 1. GENERAL

475-1.1 SCOPE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1475-1.2 SAFETY PRECAUTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1475-1.2.1 SAFETY, DETAILED PROCEDURES AND PRECAUTIONS . . 1-1475-1.2.2 FIRE HAZARD DURING DEPERMING . . . . . . . . . . . . . . . . . . . 1-1475-1.2.2.1 Precautions for the Prevention of Fire. . . . . . . . . . . . . . . . . . . 1-1475-1.2.2.2 Fire Watch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1475-1.2.2.3 Cable and Solenoid Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2475-1.2.2.4 Type of Connections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2475-1.2.2.5 Care in Rigging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2475-1.2.2.6 Protection and Location of Connections. . . . . . . . . . . . . . . . . . 1-2475-1.2.2.7 Electrical Loading of Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2475-1.2.2.8 Additional Special Precautions . . . . . . . . . . . . . . . . . . . . . . . . 1-2475-1.2.3 HEALTH THREAT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

SECTION 2. DEGAUSSING PRINCIPLES

475-2.1 MAGNETIC FIELD OF EARTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1475-2.1.1 LINES OF FORCE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1475-2.1.2 MAGNETIC UNITS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1475-2.1.3 RESOLUTION INTO COMPONENTS. . . . . . . . . . . . . . . . . . . . . 2-3475-2.1.3.1 Horizontal Component - Earth’s Field . . . . . . . . . . . . . . . . . . . 2-3475-2.1.3.2 Vertical Component - Earth’s Field . . . . . . . . . . . . . . . . . . . . . 2-3475-2.2 MINE SENSING OF A SHIP’S MAGNETIC FIELD . . . . . . . . . . . . 2-3475-2.3 REASONS FOR DEGAUSSING . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3475-2.4 DEGAUSSING METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4475-2.5 MAGNETIC TREATMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4475-2.6 MAGNETIC TREATMENT EFFECTIVENESS . . . . . . . . . . . . . . . . 2-4475-2.7 SHIP’S MAGNETIZATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4475-2.7.1 SHIP’S PERMANENT MAGNETIZATION . . . . . . . . . . . . . . . . . 2-4475-2.7.1.1 Reduction of Permanent Magnetization by Magnetic Treat-

ment (Deperming) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4475-2.7.1.2 Components of Permanent Magnetization . . . . . . . . . . . . . . . 2-4475-2.7.1.3 Permanent Magnetization - Effects of Heading or Latitude . 2-4475-2.7.2 SHIP’S INDUCED MAGNETIZATION . . . . . . . . . . . . . . . . . . . . 2-4

S9086-QN-STM-010/CH-475

ii

475-2.7.2.1 Longitudinal Component Effects of Latitude . . . . . . . . . . . . . 2-5475-2.7.2.2 Longitudinal Component Effects of Heading . . . . . . . . . . . . . 2-5475-2.7.2.3 Longitudinal Component Effects of Pitch . . . . . . . . . . . . . . . . 2-5475-2.7.2.4 Athwartship Component. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5475-2.7.2.5 Athwartship Component Effects of Heading . . . . . . . . . . . . . . 2-5475-2.7.2.6 Athwartship Component Effects of Roll . . . . . . . . . . . . . . . . . 2-6475-2.7.2.7 Vertical Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6475-2.7.2.8 Vertical Component Effects of Heading. . . . . . . . . . . . . . . . . . 2-6475-2.7.2.9 Vertical Component Effects of Pitch and Roll . . . . . . . . . . . . . 2-6475-2.7.2.10 Summary of Field Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6475-2.8 SHIPBOARD DEGAUSSING SYSTEM . . . . . . . . . . . . . . . . . . . . . . 2-6

SECTION 3. DEGAUSSING COILS

475-3.1 COIL FUNCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1475-3.2 MAGNETIC FIELD FROM CURRENT-COIL CONVENTIONS. . . 3-1475-3.3 M-COIL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1475-3.3.1 M-COIL PURPOSE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1475-3.3.2 VERTICAL MAGNETIZATION AND M-COIL FIELD . . . . . . . . 3-2475-3.3.2.1 M-Coil Field Variability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2475-3.3.2.2 M-Coil Field Variability with Pitch and Roll. . . . . . . . . . . . . . 3-2475-3.4 F- AND Q-COILS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3475-3.4.1 LONGITUDINAL MAGNETIZATION AND THE F-AND Q-

COILS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3475-3.4.2 F- AND Q-COIL FIELD VARIABILITY . . . . . . . . . . . . . . . . . . . . 3-3475-3.5 FI-QI AND FP-QP COILS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3475-3.5.1 FI-QI AND FP-QP FIELD VARIABILITY . . . . . . . . . . . . . . . . . . 3-4475-3.6 L-COIL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4475-3.6.1 L-COIL PURPOSE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4475-3.6.1.1 L-Coil Field Variability with Pitch. . . . . . . . . . . . . . . . . . . . . . 3-4475-3.6.1.2 L-Coil Field Variability with Heading or Magnetic Latitude. 3-4475-3.7 A-COIL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4475-3.7.1 A-COIL PURPOSE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5475-3.8 P-COIL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5475-3.9 AUXILIARY COILS (MX, AX, LX, PX) . . . . . . . . . . . . . . . . . . . . . . . 3-5475-3.10 NUMBER OF COILS USED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5475-3.11 COIL FIELD STRENGTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5475-3.11.1 METHODS TO CHANGE COIL FIELD STRENGTH. . . . . . . . . 3-5475-3.12 SINGLE CONDUCTOR AND MULTICONDUCTOR COILS . . . . . 3-6475-3.12.1 SINGLE-CONDUCTOR COILS . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6475-3.12.2 MULTICONDUCTOR COILS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6475-3.13 DEGAUSSING COIL POLARITY, MARKING AND DESIG-

NATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6475-3.13.1 DIRECTION OF ELECTRIC CURRENT. . . . . . . . . . . . . . . . . . . 3-6475-3.13.1.1 Degaussing Polarity Indicators . . . . . . . . . . . . . . . . . . . . . . . . 3-6475-3.13.1.2 Polarity Indicator Precautions . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

S9086-QN-STM-010/CH-475

iii

475-3.13.2 COIL POLARITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6475-3.13.2.1 A Coil Polarity Convention . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6475-3.13.2.2 L-Coil Polarity Convention . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7475-3.13.2.3 FI and QI Coil Loop Polarity Convention . . . . . . . . . . . . . . . . 3-7475-3.13.2.4 FP and QP Coil Loop Polarity Conventions. . . . . . . . . . . . . . . 3-7475-3.13.2.5 Ammeter Deflection Convention . . . . . . . . . . . . . . . . . . . . . . . 3-7475-3.13.3 MARKING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7475-3.13.4 LOOP DESIGNATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7475-3.13.5 CIRCUIT DESIGNATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8475-3.13.5.1 Circuits of Four-turn Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8475-3.13.5.2 Conductor Circuit Designation. . . . . . . . . . . . . . . . . . . . . . . . . 3-8475-3.13.6 COIL CABLE DESIGNATION . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8475-3.13.6.1 Degaussing Coil Cable Section Number . . . . . . . . . . . . . . . . . 3-10475-3.13.7 FEEDER CABLE DESIGNATION . . . . . . . . . . . . . . . . . . . . . . . . 3-10475-3.13.7.1 Power Supply Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10475-3.13.7.2 Interconnecting Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10475-3.13.7.3 Compass Compensating Coil and Indicator Light Cables . . . 3-10475-3.13.8 OTHER CABLE DESIGNATION . . . . . . . . . . . . . . . . . . . . . . . . . 3-10475-3.13.9 CONDUCTOR DESIGNATION . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12475-3.13.9.1 Single Conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12475-3.13.9.2 Spare Conductors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12475-3.13.9.3 Parallel Conductors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12475-3.13.9.4 Positive and Negative Geometric Polarity. . . . . . . . . . . . . . . . 3-12475-3.13.10 FEEDER CABLE CONDUCTOR DESIGNATION . . . . . . . . . . . 3-14475-3.13.10.1 Power Supply Cables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14475-3.13.10.2 Compass Compensation and Indicator Light Cables . . . . . . . 3-14475-3.13.11 CABLE AND CONDUCTOR TAGS, NAVAL SHIPS. . . . . . . . . . 3-14475-3.13.12 CABLE AND CONDUCTOR TAGS, MERCHANT SHIPS . . . . . 3-14475-3.13.13 CONNECTION AND THROUGH BOXES . . . . . . . . . . . . . . . . . . 3-14475-3.13.13.1 Definitions - Connection Box . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14475-3.13.13.2 Definition - Through Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16475-3.13.13.3 Numbering. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16475-3.13.13.4 A-Coil and Box Numbering. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16475-3.13.13.5 L-Coil and Box Numbering. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16475-3.13.14 IDENTIFICATION PLATES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16475-3.13.15 WIRING DIAGRAM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-16475-3.14 REQUIRED COIL CURRENT ALGORITHM. . . . . . . . . . . . . . . . . . 3-17

SECTION 4. DEGAUSSING CONTROL EQUIPMENT

475-4.1 OPERATOR CURRENT CONTROL - PRIOR TO MID-1950SEQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

475-4.2 MANUAL CURRENT ADJUSTMENT EQUIPMENT . . . . . . . . . . . 4-1475-4.3 AUTOMATIC CURRENT CONTROL EQUIPMENT. . . . . . . . . . . . 4-1475-4.3.1 MAGNETOMETER CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1475-4.3.1.1 Magnetometer Control on Nonmagnetic Minesweepers . . . . . 4-1

S9086-QN-STM-010/CH-475

iv

475-4.3.1.2 Magnetometer Control on Special Steel Hull Ships . . . . . . . . 4-2475-4.3.2 GYRO CONTROL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2475-4.3.2.1 Gyro Control - Induced Field . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2475-4.3.2.2 Gyro Control - Perm Field . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2475-4.3.3 EMERGENCY MANUAL CONTROL. . . . . . . . . . . . . . . . . . . . . . 4-2475-4.4 EQUIPMENT DESCRIPTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2475-4.4.1 TYPE MDG. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2475-4.4.2 TYPE SSM EQUIPMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2475-4.4.2.1 SSM Control Equipment Description . . . . . . . . . . . . . . . . . . . 4-3475-4.4.2.2 SSM Power Control Equipment . . . . . . . . . . . . . . . . . . . . . . . . 4-7475-4.4.3 TYPE MCD. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7475-4.5 DEGAUSSING EQUIPMENT OPERATION, GENERAL . . . . . . . . 4-7475-4.5.1 ESSENTIAL POINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7475-4.5.2 MAGNETOMETER-CONTROLLED AUTODEG EQUIPMENT

OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7475-4.5.2.1 Automatic Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7475-4.5.2.2 Automatic Performance Checks . . . . . . . . . . . . . . . . . . . . . . . . 4-8475-4.5.2.3 Manual Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-9475-4.5.2.4 Technical Manual Consultation for Exact Procedures . . . . . . 4-10475-4.5.3 GYRO-CONTROLLED AUTODEG EQUIPMENT OPERATION 4-10475-4.5.3.1 Automatic Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-10475-4.5.3.2 Automatic Operation Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-11475-4.5.3.3 Automatic Operation Performance Checks . . . . . . . . . . . . . . . 4-11475-4.5.3.4 Manual Operation of Gyro-controlled Equipment. . . . . . . . . . 4-11475-4.5.3.5 Manual Operation Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12475-4.5.4 OPERATOR CURRENT CONTROL EQUIPMENT . . . . . . . . . . 4-12475-4.5.4.1 General Procedures. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-12475-4.5.4.2 Detailed Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-13

SECTION 5. DEGAUSSING SYSTEM MAINTENANCE

475-5.1 PREVENTIVE MAINTENANCE. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1475-5.2 CORRECTIVE MAINTENANCE. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1475-5.2.1 DEGAUSSING COILS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1475-5.2.2 CONTROL AND POWER EQUIPMENT . . . . . . . . . . . . . . . . . . . 5-1475-5.3 TECHNICAL INFORMATION SOURCES, DEGAUSSING

EQUIPMENT AND SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

SECTION 6. MAGNETIC RANGES AND RANGING

475-6.1 RANGE DESCRIPTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1475-6.2 PURPOSE OF RANGING-CHECK RANGING. . . . . . . . . . . . . . . . . 6-1475-6.3 PURPOSE OF RANGING - CALIBRATION. . . . . . . . . . . . . . . . . . . 6-1475-6.4 FREQUENCY OF RANGING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1475-6.5 SHIP’S RESPONSIBILITIES FOR ACCURATE RANGING. . . . . . 6-1475-6.6 MINESWEEPER OFF-LOAD PROCEDURES . . . . . . . . . . . . . . . . . 6-1

S9086-QN-STM-010/CH-475

v

475-6.7 SHIP’S DEGAUSSING FOLDER. . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2475-6.7.1 DEGAUSSING FOLDER CONTENT . . . . . . . . . . . . . . . . . . . . . . 6-2475-6.7.2 DEGAUSSING FOLDER PREPARATION BY DEGAUSSING

RANGE PERSONNEL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

SECTION 7. MAGNETIC TREATMENT

475-7.1 TYPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1475-7.1.1 DEPERMING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1475-7.1.2 FLASH-D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1475-7.2 EFFECTIVENESS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1475-7.3 FREQUENCY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1475-7.4 SHIP’S RESPONSIBILITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1475-7.4.1 SPECIAL PRECAUTIONS DURING MAGNETIC TREAT-

MENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1475-7.4.2 EQUIPMENT AND ORDNANCE PRECAUTIONS . . . . . . . . . . 7-2475-7.4.3 SUBMARINE GENERIC EQUIPMENT PRECAUTIONS . . . . . 7-2475-7.4.3.1 Effects on Computers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2475-7.4.3.2 Effects of Other Magnetic Elements . . . . . . . . . . . . . . . . . . . . 7-2475-7.4.3.3 Effects on Cathode Ray Tube (CRT) Displays . . . . . . . . . . . . . 7-2475-7.4.4 SPECIFIC SUBMARINE WEAPONS PROTECTION PROCE-

DURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3475-7.4.4.1 Strategic Weapons Protection . . . . . . . . . . . . . . . . . . . . . . . . . 7-3475-7.4.4.2 MK48 ADCAP Torpedo Procedures During Deperming/ Flash

Magnetic Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3475-7.4.4.3 TOMAHAWK Missile

Offload and Protection Procedures During Deperming/FlashMagnetic Treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

475-7.4.5 SPECIFIC SUBMARINE EQUIPMENT PROTECTION PRO-CEDURES DURING DEPERMING/ FLASH MAGNETICTREATMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

475-7.4.6 SURFACE SHIP GENERIC EQUIPMENT PRECAUTIONS. . . 7-7475-7.4.6.1 Effects on Computers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7475-7.4.6.2 Effects on Other Magnetic Elements . . . . . . . . . . . . . . . . . . . . 7-7475-7.4.6.3 Effects on Cathode Ray Tube (CRT) Displays . . . . . . . . . . . . . 7-7475-7.4.7 SPECIFIC SURFACE SHIP WEAPONS PROTECTION PRO-

CEDURES DURING DEPERMING MAGNETIC TREATMENT 7-8475-7.4.8 SPECIFIC SURFACE SHIP INSTALLED EQUIPMENT PRO-

TECTION PROCEDURES DURING DEPERMING MAG-NETIC TREATMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

475-7.4.9 CLEARANCE OF AMMUNITION, PYROTECHNICS, EX-PLOSIVES, AND INFLAMMABLE MATERIALS. . . . . . . . . . . . 7-11

475-7.4.10 CLEARANCE OF FUEL OIL BUNKERS . . . . . . . . . . . . . . . . . . 7-11475-7.4.11 RESTRICTIONS ON THE MAGNETIC TREATMENT OF

TANKERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11475-7.4.12 RESTRICTION ON DEPERMING OF SHIPS (OTHER THAN

TANKERS) THAT CARRY COMBUSTIBLE LIQUIDS WITH AFLASH POINT BELOW 66 DEGREES C . . . . . . . . . . . . . . . . . . 7-11

S9086-QN-STM-010/CH-475

vi

475-7.4.13 RESTRICTIONS ON MAGNETIC TREATMENT OF SHIPSCARRYING EXPLOSIVES AS CARGO . . . . . . . . . . . . . . . . . . . . 7-12

475-7.5 DEGAUSSING FOLDER FOR DEPERMED SHIPS . . . . . . . . . . . . 7-12

SECTION 8. COMPASS COMPENSATING INSTALLATION

475-8.1 PURPOSE/DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1475-8.1.1 VERTICAL COMPONENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1475-8.1.2 HORIZONTAL COMPONENT . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1475-8.1.2.1 Horizontal Component Error . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1475-8.1.2.2 Horizontal Component Error Compensation. . . . . . . . . . . . . . 8-1475-8.1.3 INTERCARDINAL COIL COMPENSATION . . . . . . . . . . . . . . . 8-1475-8.1.4 COMPENSATION CURRENT RELATIONSHIP TO THE

DEGAUSSING CURRENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2475-8.1.5 COMPENSATING COIL CONSTRUCTION . . . . . . . . . . . . . . . . 8-2475-8.1.6 TYPES OF COILS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2475-8.1.6.1 Acceptable Old-Style Compass Compensation Coils. . . . . . . . 8-3475-8.1.6.2 Standard Present Types of Compass Compensation Coils . . . 8-3475-8.1.7 COIL POWER SUPPLY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3475-8.1.8 CONTROL BOXES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-3475-8.1.8.1 Type A and Type A-1 Control Box Wiring Diagrams . . . . . . . 8-3475-8.1.8.2 Type K-2 and Type R-2 Compass Coils Wiring Diagrams . . . 8-3475-8.2 INSTALLATION AND COMPASS COMPENSATION . . . . . . . . . . 8-4475-8.2.1 INSTALLATION PERSONNEL . . . . . . . . . . . . . . . . . . . . . . . . . . 8-4475-8.2.2 COMPASS COMPENSATION PERSONNEL . . . . . . . . . . . . . . . 8-4475-8.2.3 DOCKSIDE COMPENSATION LOCATION . . . . . . . . . . . . . . . . 8-4475-8.2.3.1 DOCKSIDE COMPENSATION CONDITIONS . . . . . . . . . . . 8-4475-8.2.3.2 Optimum Dockside Compensation. . . . . . . . . . . . . . . . . . . . . . 8-5475-8.2.4 FINAL COMPENSATION LOCATION . . . . . . . . . . . . . . . . . . . . 8-5475-8.2.5 COMPASS COMPENSATION TECHNIQUE . . . . . . . . . . . . . . . 8-5475-8.2.6 FINAL COMPENSATION TECHNIQUE . . . . . . . . . . . . . . . . . . 8-5475-8.2.6.1 Swing for Deviation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6475-8.2.6.2 Intercardinal Coil Compensation Headings . . . . . . . . . . . . . . 8-6475-8.2.6.3 Component Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6475-8.2.6.4 Reduction of Residual Magnetism by Reversals . . . . . . . . . . . 8-6475-8.2.6.5 Compensation Adjustments . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9475-8.2.6.6 Deflecting Compass for Horizontal Components. . . . . . . . . . . 8-9475-8.2.6.7 Deflecting Magnet Placement . . . . . . . . . . . . . . . . . . . . . . . . . 8-11475-8.2.6.8 NE and NW Component Compensation. . . . . . . . . . . . . . . . . . 8-11475-8.2.6.9 NE Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11475-8.2.6.10 NW Component . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11475-8.2.6.11 Check for Resistor Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-11475-8.2.6.12 Check for Residuals. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12475-8.2.6.13 Securing by Reversal Documentation . . . . . . . . . . . . . . . . . . . 8-12475-8.2.6.14 Final Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12475-8.2.7 ACCURACY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-12

S9086-QN-STM-010/CH-475

vii

475-8.2.8 ASYMMETRICAL DEVIATIONS. . . . . . . . . . . . . . . . . . . . . . . . . 8-15475-8.2.8.1 Asymmetrical Deviation Compensation Technique . . . . . . . . 8-15475-8.2.8.2 Binnacle Position Check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-15475-8.2.9 BINNACLE POSITION OUT OF TOLERANCE . . . . . . . . . . . . . 8-15475-8.2.10 PRECAUTIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-15475-8.2.10.1 Maximum Currents, Type A Control Box Resistors . . . . . . . . 8-15475-8.2.10.2 Maximum Currents, Type A-1 Control Box Resistors . . . . . . 8-15475-8.2.10.3 Maximum Coil Currents, Type K, K-1, K-2, R-1 and R-2 Coil

Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16475-8.2.11 FORWARDING OF FORMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16475-8.3 OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16475-8.4 MAINTENANCE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16475-8.4.1 COMPASS COMPENSATING COILS . . . . . . . . . . . . . . . . . . . . . 8-16475-8.4.2 CONTROL BOXES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-16475-8.4.2.1 Control Box Maintenance Procedure . . . . . . . . . . . . . . . . . . . . 8-17475-8.4.2.2 Connecting Cables. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17475-8.4.2.3 Reports. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17475-8.4.2.4 Compass Coil Troubleshooting . . . . . . . . . . . . . . . . . . . . . . . . . 8-17475-8.4.2.5 Locating Grounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-17

APPENDIX AREFERENCE PUBLICATIONS

S9086-QN-STM-010/CH-475

viii

S9086-QN-STM-010/CH-475

ix

LIST OF ILLUSTRATIONS

Figure Page475-2-1 Earth’s Magnetic Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2475-2-2 Horizontal and Vertical Components of the Earth’s Magnetic Field. . . . . . 2-3475-2-3 Longitudinal Magnetization.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-5475-2-4 Athwartship Magnetization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-6475-3-1 Magnetic Field Around a Conductor Carrying Current. . . . . . . . . . . . . . . . 3-1475-3-2 Magnetic Field of Coil Carrying Current. . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1475-3-3 M- or Main Coil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2475-3-4 Magnetic Field due to Vertical Magnetization of Ship. . . . . . . . . . . . . . . . . 3-2475-3-5 Magnetic Field due to M-Coil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2475-3-6 F- and Q-Coils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3475-3-7 Longitudinal Field of Ship on North Heading and Neutralizing Fields of

F- and Q-Coils. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3475-3-8 L- or Longitudinal Coil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4475-3-9 A- or Athwartship Coil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4475-3-10 Numbering M-Coil Loops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7475-3-11 Numbering F- and Q-Coil Loops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7475-3-12 M-Coil With a Single Circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8475-3-13 M-Coil With Two Parallel Circuits. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8475-3-14 Degaussing Coil Cable Designations, Typical. . . . . . . . . . . . . . . . . . . . . . . . 3-11475-3-15 Typical M-Coil Connection Box. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13475-3-16 Feeder Cable Conductor Designation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15475-4-1 Type MDG Automatic Degaussing Equipment. . . . . . . . . . . . . . . . . . . . . . . 4-4475-4-2 Block Diagram for Type MDG Degaussing System. . . . . . . . . . . . . . . . . . . 4-5475-4-3 Type SSM Automatic Degaussing Equipment. . . . . . . . . . . . . . . . . . . . . . . 4-6475-4-4 Block Diagram for Type SSM Degaussing Switchboard.. . . . . . . . . . . . . . . 4-8475-4-5 Block Diagram for Type SSM Degaussing Power Supply.. . . . . . . . . . . . . . 4-8475-8-1 Degaussing Coil Magnetic Field Effect. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2475-8-2 Compensation of Intercardinal Components of Degaussing Coil Magnetic

Field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-2475-8-3 Type K-2 Compensating Coil Assembly and Type A-1 Control Box.. . . . . . 8-3475-8-4 Type A Control Box Wiring Diagram.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-5475-8-5 Type A-1 Control Box Wiring Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-6475-8-6 Type K-2 Coil Wiring Diagram. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7475-8-7 Type R-2 Coil Wiring Diagram.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-8475-8-8 Compass Compensating Coil Data, NAVSEA Form 8950/40. . . . . . . . . . . . 8-10475-8-9 Deflecting Compass With Permanent Magnet. . . . . . . . . . . . . . . . . . . . . . . 8-12475-8-10 Magnetic Compass Table, NAVSEA Form 3120/4. (Sheet 1 of 2) (shown

oversize for clarity) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-13

S9086-QN-STM-010/CH-475

x

S9086-QN-STM-010/CH-475

xi

LIST OF TABLES

Table Page475-2-1 Magnetic Units. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2475-3-1 Degaussing Installation Marking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9475-4-1 AUTODEG Equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3475-8-1 Standard Types of Compass Compensating Coils . . . . . . . . . . . . . . . . . . . . 8-4475-8-2 Coil Maximum Current In Any One Winding . . . . . . . . . . . . . . . . . . . . . . . 8-16

S9086-QN-STM-010/CH-475

xii

S9086-QN-STM-010/CH-475

1-1

CHAPTER 475

MAGNETIC SILENCING

SECTION 1. GENERAL

475-1.1 SCOPE

Magnetic silencing is the science of reduc-ing the magnetic/electric signature of a shipor submarine. Reduction of the static mag-netic signature is accomplished by:degaussing, constructing ships of nonmag-netic materials, and controlling eddy cur-rent fields and controlling stray fieldscaused by various items of the ship’s equip-ment. This chapter covers degaussing andmagnetic treatment. Control of eddy cur-rent fields and stray fields are covered byfleet instructions issued to nonmagneticminesweepers. This chapter is divided intoeight sections. Section 1 provides generalintroductory information and safety. Sec-tion 2 covers shipboard degaussing prin-ciples and includes the fundamental mag-netization relations. Section 3 covers allaspects of degaussing coils, including func-tion, numbering and required current. Sec-tion 4 covers current degaussing controlequipment, and section 5 follows im-mediately with maintenance of degaussingcontrol equipment. Section 6 is a discussionof magnetic ranges and ranging, and sec-tion 7 discusses magnetic treatment andthe requirements for its implementation.The final entry, section 8, discusses com-pass compensation techniques of newly in-stalled or repaired compasses, as well asmaintenance and operation data.

475-1.2 SAFETY PRECAUTIONS

475-1.2.1 SAFETY, DETAILED PRO-CEDURES AND PRECAUTIONS.Safety precautions must be observed whenworking around electrical equipment toavoid injury to personnel and equipment.

NSTM Chapter 300, Electric PlantGeneral, provides detailed procedures andprecautions. Also refer to OPNAVINST5100.19, Navy Occupational Safety andHealth (NAVOSH) Program Manual forForces Afloat.

475-1.2.2 FIRE HAZARD DURINGDEPERMING. A magnetic treatmentoperation presents a considerable firehazard to any ship being treated since thedeperming cables carry currents greatly inexcess of their continuous rating, and thehandling and immersion of the cables inseawater makes it difficult to maintain ade-quate insulation of the cables over an ex-tended period. Extreme care in every detailmust be exercised by all persons engaged inthe operation. If the ship is carrying or hasrecently carried combustible liquid of anykind, or is loaded with explosives, thehazards are greatly increased and, undercertain circumstances described in475-7.4.13, magnetic treatment must not becarried out.

475-1.2.2.1 Precautions for thePrevention of Fire. The specificprecautions given in the remainder of thissection should be observed by all ships andfacility personnel.

475-1.2.2.2 Fire Watch. During mag-netic treatment, a fire watch should beplaced so that all connections can be kept inview during each shot and so that the entiresolenoid (coils of wire around the ship)above water can be viewed at least once pershot. Make sure that the members of thiswatch are able to communicate rapidly withthe deperming control room.

S9086-QN-STM-010/CH-475

1-2

475-1.2.2.3 Cable and SolenoidTesting. The cables used in the mag-netic treatment solenoid must be testedelectrically at frequent intervals (in thecase of hazardous ships, just before rigging)- see paragraphs 475-7.4.11 through475-7.4.13 to identify flaws in the insula-tion. Defective cable should be rejected andnot used until it is repaired and satisfac-torily passes the electrical test. After rig-ging, the resistance to ground of the entiresolenoid should be measured. Faults shallbe rectified before any shot is applied.

475-1.2.2.4 Type of Connections.Burndy Hypress or other similar types ofconnections should be used, rather thanlugs that are held to the cables only bysolder.

475-1.2.2.5 Care in Rigging. Usecare in rigging to prevent damage to thecable insulation and the lugs or connectors.Rollers should be used where it is necessaryto pull the cables over the edges of hullplating, piers, gunwales of work boats orother sharp edges. Chafing gear should beprovided wherever the rigged cable restsacross sharp edges above water such as theedge of hull plating and hatch combings.Particular care should be exercised in pull-ing cables over bilge keels.

475-1.2.2.6 Protection and Locationof Connections. Connections betweenlengths of cable should be housed in insu-lating boots extending at least 0.1 meterbeyond live parts on each side. The connec-tion should be placed on an insulating sur-

face. There should be no appreciable axialtension between the cables through the con-nections. Connections should be placed sothat each one can be kept in view by theFire Watch.

475-1.2.2.7 Electrical Loading ofCables. To prevent deterioration of thecable insulation with its consequent firehazard and to reduce the direct fire hazardfrom overheated cables, the maximum cur-rents and current durations (shot) shall notbe exceeded. To prevent the possibility ofinsulation puncture by voltage surges, thecurrent should not be switched off from fullvalue with a circuit breaker. The currentshould be switched off by adequate rectifiercontrol circuits.

475-1.2.2.8 Additional SpecialPrecautions. It is desirable to use anelectrical device to sound an alarm or tripthe circuit breaker if the resistance of thesolenoid to ground falls below a predeter-mined value at any time during the mag-netic treatment. A signal system such as abuzzer or bell that sounds only when a mag-netic treatment shot is on shall be usedduring the treatment operation.

475-1.2.3 HEALTH THREAT.Unnecessary exposure to high magneticfields should be avoided. The dc magneticfield generated during the depermingprocess is well within the normally con-sidered safe limit for personnel.

S9086-QN-STM-010/CH-475

2-1

SECTION 2. DEGAUSSING PRINCIPLES

475-2.1 MAGNETIC FIELD OFEARTH

The earth’s magnetic field primarily in-duces magnetization in ships. Like anymagnetic field, the earth’s can be brokendown into lines of force and units of fieldstrength that can be resolved into com-ponents.

475-2.1.1 LINES OF FORCE. Themagnetic field of earth can be representedby lines of force as indicated in figure475-2-1. By convention, the external direc-tion of the magnetic field of a bar magnet isfrom its north pole to its south pole. Linesof force for the earth’s field, however, leavethe earth in the Antarctic regions andreenter in the Arctic regions. For thisreason, it is necessary to think of the polarregion in the Arctic as the geographic-north, magnetic-south pole of a magnet.The direction of the field at any point istangent to the line of force through thepoint. The field is strong where the lines offorce are close together and weak wherethey are far apart.

475-2.1.2 MAGNETIC UNITS.Units of magnetism are concerned with themagnetizing force (H), with magnetic flux(φ), and with flux density (B).

a. Magnetizing force (H) - The magneticintensity at a point in a magnetic field. Amagnetizing force may be produced by thealignment of magnetic domains in a mag-netic substance (magnet) or by an electricalcurrent in a conductor of a coil.

b. Magnetic flux (φ) - Magnetic flux isthe number of lines of magnetic force set upin a magnetic substance.

c. Magnetic flux density (B) - Flux den-sity is the flux per unit area normal to thedirection of flux.

The magnetizing force and the magneticflux density are related in free space, or ap-proximately in air as:

B = µoH

,

where µo is the permeability of free space.For purpose of this publication, free spacecan be considered vacuum, air, seawater, orfreshwater.

In any material, the magnetizing force andthe magnetic flux density are related as:

B = µrµoH = µH

,

where µr is the relative permeability of thematerial or µ/µo, and µ is the absolute per-meability of the material, which maychange with flux density. (In free space, µ= µo and µr = 1.) Mu (µ) of a magneticmaterial may be 2,000 times higher thanµo, so higher flux densities may be obtainedin a magnetic material than in free space orair for the same magnetizing force.

The units of magnetic phenomena havebeen standardized to those that originatewith mks (meter-kilogram-second) derivedunits instead of the units originating fromthe previously derived cgs (centimeter-gram-second) units. Table 475-2-1 lists theolder cgs units and the newer, preferred,mks units, with some benchmark magneticfields and relations.

The preferred unit for magnetic fields is thetesla (traditionally called the gauss). Thegauss is so firmly embedded in degaussingterminology, however, that it is not uncom-mon to speak of magnetic fields as beingmeasured in gauss. One tesla is equal to10,000 gauss.

S9086-QN-STM-010/CH-475

2-2

Figure 475-2-1. Earth’s Magnetic Field.

TABLE 475-2-1. MAGNETIC UNITS

Magneticfield

intensityMagnetic

fluxFlux

density Relations

Symbol H φ B

CGS unitnon-preferred

Oerstedor

ampere-turn/meter

Maxwellor

line offorce

Gaussor

maxwell/cm2

B = µH

ϕ = BA (m2)

SI (MKS)unitpreferred

Ampere/meter

Weber Teslaor

weber/m2

µo = 4π x 10-7

µ = µr µo

Earth’smagneticfield

40 ampere/meter

or0.5 oersted

****************************************************

50 microteslaor

0.5 gauss

In free space:B = µoH(µr = 1)

Depermingmagneticfield (Inair)

1600 ampere/meter

or20 oersted

****************************************************

2 milliteslaor

20 gauss

In a material:B = µrµoH(incremental)

S9086-QN-STM-010/CH-475

2-3

475-2.1.3 RESOLUTION INTOCOMPONENTS. At any point on thesurface of the earth, the magnetic field canbe resolved into a horizontal and a verticalcomponent (see figure 475-2-2).

Figure 475-2-2. Horizontal andVertical Components

of the Earth’sMagnetic Field.

475-2.1.3.1 Horizontal Component -Earth’s Field. The horizontal compo-nent of the earth’s magnetic field:

a. Is always directed from the earth’ssouth magnetic pole to the earth’s northmagnetic pole. (See figure 475-2-1.)

b. Is zero at the magnetic poles.

c. Is a maximum at the magneticequator.

d. Is always positive.

e. Is referred to as the H (for horizon-tal) field (not to be confused with magneticfield intensity, H).

475-2.1.3.2 Vertical Component -Earth’s Field. The vertical compo-nent of the earth’s magnetic field:

a. Is directed radially outward (up-ward), south of the magnetic equator.

b. Is directed radially inward(downward), north of the magnetic equator.

c. Is zero at the magnetic equator.

d. Is a maximum at the magnetic poles.

e. Is positive in the northern hemi-sphere and negative in the southern hemi-sphere.

f. Is referred to as the Z-field.

475-2.2 MINE SENSING OF ASHIP’S MAGNETIC FIELD

A ship is a magnet because it has magneticmaterial (steel) in its hull, machinery, andcargo. Like any other magnet, the ship issurrounded by a magnetic field that isstrong near the ship but decreases greatlywith distance from the ship. It is this mag-netic field that actuates magnetic influencedevices that can be used to detect thepresence of the ship. The magnetic in-fluence devices may form part of a magneticdetector whose function is merely to detectthe presence of a ship, or they may formpart of the firing mechanism of a magneticmine and cause it to explode when a ship isnear. Physical contact is not necessary toactuate magnetic influence devices.

475-2.3 REASONS FOR DEGAUSS-ING

Degaussing is done to counteract the ship’smagnetic field so that it seems, as nearly aspossible, as if the ship were not there mag-netically. If this condition could be per-fectly achieved, a magnetic influence devicecould not detect the presence of the ship.Even though the ship’s magnetic field can-not be completely eliminated, degaussing

S9086-QN-STM-010/CH-475

2-4

decreases the danger to ships from mag-netic weapons.

475-2.4 DEGAUSSING METHODS

A ship can be degaussed either by magnetictreatment or by providing a shipboarddegaussing installation or by both.

475-2.5 MAGNETIC TREATMENT

Ships that require degaussing by magnetictreatment called flash-D are periodicallytreated at degaussing facilities to providesome measure of protection against mag-netic mines and magnetic anomaly detec-tion (MAD). These ships do not have equip-ment permanently installed and, therefore,nothing concerning degaussing has to beoperated and maintained by the ships’forces. Ships that do not have permanentlyinstalled degaussing equipment requiredeperming to reduce and stabilize per-manent magnetizations.

475-2.6 MAGNETIC TREATMENTEFFECTIVENESS

Degaussing by magnetic treatment does notprotect against magnetic mines as effec-tively as a shipboard degaussing systemand this treatment is used only to a limitedextent. Magnetic treatment is furtherdescribed in section 7.

475-2.7 SHIP’S MAGNETIZATION

A ship’s magnetic field is caused in part bythe ship’s permanent magnetization and inpart by the ship’s induced magnetization.

475-2.7.1 SHIP’S PERMANENTMAGNETIZATION. Ships are builtunder the influence of the magnetic field ofthe earth and as a result become per-manently magnetized. A ship’s permanentmagnetization depends on the magnetic

field at the place where the ship was built,the orientation of the ship with respect tothe magnetic field of earth, the material theship was constructed of, and a number ofother factors.

475-2.7.1.1 Reduction of PermanentMagnetization by Magnetic Treat-ment (Deperming). All ships thathave a degaussing installation, and somethat do not require degaussing instal-lations, are magnetically treated. Thistreatment is essentially a large-scale ver-sion of demagnetizing a mechanical watch.Its purpose is to reduce permanent mag-netization and bring all ships of the sameclass into a standard condition in which thepermanent magnetization that remainsafter treatment is approximately the samefor all ships of that class.

475-2.7.1.2 Components of Per-manent Magnetization.Components of a ship’s permanent mag-netization are:

a. Permanent vertical magnetization.

b. Permanent longitudinal magnetiza-tion.

c. Permanent athwartship magnetiza-tion.

475-2.7.1.3 Permanent Magnetiza-tion - Effects of Heading orLatitude. The three above componentsare constant (except for slow change withtime) and are unaffected by changes inheading or magnetic latitude.

475-2.7.2 SHIP’S INDUCEDMAGNETIZATION. Magnetizationis induced in a body of magnetic materialwhen it is brought into a magnetic field.The induced magnetization depends on thestrength of the magnetic field and theorientation of the body of magnetic material

S9086-QN-STM-010/CH-475

2-5

with respect to the inducing field. The in-duced magnetization is divided into threecomponents: longitudinal, athwartship andvertical.

475-2.7.2.1 Longitudinal ComponentEffects of Latitude. Longitudinalcomponents are affected by magneticlatitude. For example, consider a shipheaded magnetic north: the horizontalcomponent of the magnetic field of earth in-duces a north pole in the bow and a southpole in the stern (see figure 475-2-3) or in-duces a longitudinal (fore and aft) compo-nent of magnetization. The stronger thehorizontal component of the magnetic field,the greater the longitudinal component ofmagnetization. If the ship starts at theearth’s south magnetic pole and headsnorth, the longitudinal component of the in-duced magnetization starts at zero at theearth’s south magnetic pole, increases to amaximum at the magnetic equator, anddecreases to zero at the earth’s north mag-netic pole. Thus, for a constant heading,the longitudinal component changes whenthe ship moves to a position where thehorizontal component of the magnetic fieldis different, or as it is commonly expressed,when the ship changes its magneticlatitude.

475-2.7.2.2 Longitudinal Compo-nent Effects of Heading. If, at agiven magnetic latitude, the ship changesits heading from north to east, the lon-gitudinal component of the induced mag-netization changes from a maximum on thenorth heading to zero on the east heading.When the ship changes its heading fromeast to south, the longitudinal componentincreases from zero on the east heading to amaximum on the south heading. On sou-therly headings, a north pole is induced atthe stern and a south pole at the bow, justthe reverse of the conditions on northerlyheadings.

Figure 475-2-3. LongitudinalMagnetization.

475-2.7.2.3 Longitudinal Compo-nent Effects of Pitch. The lon-gitudinal component of induced magnetiza-tion also changes, to some extent, as theship pitches.

475-2.7.2.4 AthwartshipComponent. The earth’s field inducesan arthwartship component of a north poleon the port side and a south pole on thestarboard side when a ship is on an eastheading (figure 475-2-4). This is the ath-wartship component of induced magnetiza-tion. Its magnitude depends on thestrength of the longitudinal component ofthe magnetic field of the earth where themagnetic field is at a maximum at the mag-netic equator and zero at the magneticpoles.

475-2.7.2.5 Athwartship ComponentEffects of Heading. The ath-wartship component also changes when theheading changes. Its strongest magnitudeis when the ship is headed magnetic east or

S9086-QN-STM-010/CH-475

2-6

Figure 475-2-4. AthwartshipMagnetization.

west, and zero magnitude is present whenthe ship is headed magnetic north or south.

475-2.7.2.6 Athwartship ComponentEffects of Roll. The athwartshipcomponent of induced magnetization alsochanges, to some extent, as the ship rolls.

475-2.7.2.7 Vertical Component.Vertical components of the magnetic field ofearth are directed down when a ship isnorth of the magnetic equator. It induces avertical component of induced magnetiza-tion that is also directed down, with thenorth pole below and south pole above. Themagnitude of the vertical induced mag-netization depends on the magneticlatitude. The magnitude is maximum atthe magnetic poles and zero at the magneticequator. The vertical induced magnetiza-tion is directed down when the ship is northof the magnetic equator and up when theship is south of the magnetic equator. Thevertical induced magnetization thuschanges with magnetic latitude.

475-2.7.2.8 Vertical Component Ef-fects of Heading. Unlike lon-gitudinal and athwartship induced mag-netization, vertical induced magnetizationdoes not change with heading, since achange of heading does not change theorientation of the ship with respect to thevertical component of the magnetic field ofearth.

475-2.7.2.9 Vertical Component Ef-fects of Pitch and Roll. The verticalinduced magnetization changes, to some ex-tent, when the ship rolls or pitches.

475-2.7.2.10 Summary of FieldChanges. The three components of in-duced magnetization change as follows:

a. Longitudinal induced magnetizationchanges when either the magnetic latitudeor the heading changes, and when the shippitches.

b. Athwartship induced magnetizationchanges when either the magnetic latitudeor the heading changes, and when the shiprolls.

c. Vertical induced magnetizationchanges when the magnetic latitudechanges or when the ship rolls or pitches,but not when the heading changes.

475-2.8 SHIPBOARD DEGAUSSINGSYSTEM

A shipboard degaussing system consists ofthe following items:

a. Degaussing coils

b. A means to control coil current andstrength of magnetic field caused by coilcurrent

c. The ship’s degaussing folder toprovide information on current and turnsettings

S9086-QN-STM-010/CH-475

2-7

d. A power source to supply dc for thecoils

e. Compass compensating equipment toprevent the disturbance of magnetic com-passes by the magnetic field of the degauss-ing coils.

S9086-QN-STM-010/CH-475

2-8

S9086-QN-STM-010/CH-475

3-1

SECTION 3. DEGAUSSING COILS

475-3.1 COIL FUNCTION

Each of the components of the ship’s mag-netization produces a magnetic field in thevicinity of the ship. The function of thedegaussing coils is to produce magneticfields that are, as nearly as possible, equaland opposite to the magnetic fieldsproduced by the components of the ship’smagnetization. The result of the ship’s fieldand the field produced by the degaussingcoils is made as close to zero as possible sothat detection of the ship’s magnetic fieldby magnetic influence devices is reduced.

475-3.2 MAGNETIC FIELD FROMCURRENT-COIL CONVEN-TIONS

A straight conductor is surrounded by amagnetic field with lines of force as in-dicated in figure 475-3-1. When the conduc-tor is wound into the form of a coil, the linesof force will be as indicated in figure475-3-2. The convention used throughoutthis chapter is that current direction in aconductor connected to the terminals of abattery is from the positive terminal to thenegative terminal and known as positivecurrent. The relation between the directionof the current and the direction of the linesof magnetic force is as shown in figures475-3-1 and 475-3-2.

475-3.3 M-COIL

The M- or main coil encircles the ship in ahorizontal plane that is usually near thewater level (see figure 475-3-3).

475-3.3.1 M-COIL PURPOSE. TheM-coil produces a magnetic field that coun-teracts the magnetic field produced by thepermanent vertical and the induced verticalmagnetization of the ship.

Figure 475-3-1. Magnetic Field Arounda Conductor

Carrying Current.

Figure 475-3-2. Magnetic Field of CoilCarrying Current.

S9086-QN-STM-010/CH-475

3-2

Figure 475-3-3. M- or Main Coil.

475-3.3.2 VERTICAL MAGNETIZA-TION AND M-COIL FIELD. Figure475-3-4 illustrates the magnetic fieldproduced by the vertical magnetization of aship in the northern hemisphere near themagnetic pole. Figure 475-3-5 illustratesthe magnetic field produced by the M-coil.This is opposed to the magnetic fieldproduced by the vertical magnetization ofthe ship. If the M-coil field wereeverywhere exactly equal and opposite thefield produced by vertical magnetization,the result of the two magnetic fIelds wouldbe equal to zero. Although it is not possibleto attain such a perfect match, the result isconsiderably less than the field produced bythe vertical magnetization of the ship.

Figure 475-3-4. Magnetic Field due toVertical Magnetization

of Ship.

Figure 475-3-5. Magnetic Field due toM-Coil.

475-3.3.2.1 M-Coil FieldVariability. The permanent verticalmagnetization of a ship is constant whereasthe vertical induced magnetization varieswith the magnetic latitude and with the rolland pitch of the ship, but not with the head-ing. The combined result of the permanentand induced vertical magnetization willalso vary with the magnetic latitude andwith the roll and pitch of the ship. Con-sequently, the M-coil field strength must bechanged when the ship changes magneticlatitude in order to keep the M-coil field asnearly equal as possible and opposite to thefield produced by the ship’s vertical mag-netization.

475-3.3.2.2 M-Coil Field Variabilitywith Pitch and Roll. The change invertical magnetization caused by the rolland pitch of the ship is relatively small, andonly in special cases is it necessary tochange the M-coil field strength to compen-sate for this. The methods used to controldegaussing coil field strengths are dis-cussed in paragraphs 475-3.11 and475-3.11.1.

S9086-QN-STM-010/CH-475

3-3

475-3.4 F- AND Q-COILS

The F- or forecastle coil encircles the for-ward one-quarter to one-third of the shipand is usually just below the forecastle orother uppermost deck. The Q- or quarter-deck coil encircles the after one-quarter toone-third of the ship and is usually justbeneath the quarterdeck or other upper-most deck. These locations are shown infigure 475-3-6.

Figure 475-3-6. F- and Q-Coils.

475-3.4.1 LONGITUDINAL MAG-NETIZATION AND THE F-ANDQ-COILS. The F- and Q-coils coun-teract the lower portion of the magneticfield produced by the ship’s permanent andinduced longitudinal magnetization. Al-though the shape of the magnetic fieldproduced by the F- and Q-coils differs fromthe field produced by the ship’s longitudinalmagnetization, the two fields are, ingeneral, oppositely directed below the bowand stern of the ship (see figure 475-3-7).

475-3.4.2 F- AND Q-COIL FIELDVARIABILITY. The ship’s permanentlongitudinal magnetization is constant, butthe induced longitudinal magnetizationchanges with the heading and magneticlatitude. The F- and Q-coil field strengthsmust both be changed whenever the shipchanges either its heading or its magnetic

Figure 475-3-7. Longitudinal Field ofShip on North Heading

and NeutralizingFields of F- and

Q-Coils.

latitude, otherwise the coil field strengthswould lack the right values to counteractthe changed induced longitudinal mag-netization. Two adjustments must bemade, one to change the F-coil fieldstrength and one to change the Q-coil fieldstrength.

475-3.5 FI-QI AND FP-QP COILS

In most installations the conductors of theF and Q coil loops are connected to form twoseparate circuits, designated FI-QI coil andFP-QP coil. The FI-QI coil consists of FIloops connected in series with QI loops sothat the same current is in both. The FP-QP coil is similar. Installations with FI-QIand FP-QP coils are known as split-coil in-stallations because the F- and Q-coil loopsare each split into two coils.

S9086-QN-STM-010/CH-475

3-4

475-3.5.1 FI-QI AND FP-QP FIELDVARIABILITY. The coil fieldstrength depends on several factors:

a. The FI-QI coil is used to counteractthe magnetic field produced by the ship’slongitudinal induced magnetization. Sincethe longitudinal induced magnetizationchanges when the ship changes heading ormagnetic latitude, the strength of the FI-QIcoil must be changed accordingly.

b. The FP-QP coil is used primarily tocounteract the magnetic field produced bythe ship’s longitudinal permanent mag-netization. It is sometimes used to providesome compensation for vertical inducedmagnetization to supplement the M-coilcompensation.

c. Since the longitudinal permanentmagnetization remains unchanged whenthe ship changes heading or magneticlatitude, no change in FP-QP coil fieldstrength is needed.

d. When an FP-QP coil is used to sup-plement the M-coil compensation, its coilfield strength must be changed when theship changes magnetic latitude.

As compared to F- and Q-coils in paragraph475-3.4.2, FI-QI and FP-QP coils usually re-quire only one adjustment of coil fieldstrength, instead of two, when the shipchanges heading or magnetic latitude.

475-3.6 L-COIL

The L- or longitudinal coil resembles asolenoid. It has loops in vertical planesparallel to the frames of the ship (see figure475-3-8).

475-3.6.1 L-COIL PURPOSE. Thepurpose of the L-coil is to counteract themagnetic field produced by the ship’s lon-gitudinal permanent and induced mag-netization. It does this better than F- andQ-coils, or FI-QI and FP-QP coils. For this

Figure 475-3-8. L- or LongitudinalCoil.

reason, an L-coil is often used in mine war-fare vessels.

475-3.6.1.1 L-Coil Field Variabilitywith Pitch. An L-coil is always usedwhen compensation for pitch of the ship isrequired.

475-3.6.1.2 L-Coil Field Variabilitywith Heading or MagneticLatitude. Since the longitudinal in-duced magnetization changes when the shipchanges its heading or magnetic latitude,the L-coil field strength must be changedaccordingly. When compensation for pitchis required, the L-coil field strength mustalso be changed as the ship pitches.

475-3.7 A-COIL

The A- or athwartship coil has loops in ver-tical fore-and-aft planes (see figure475-3-9).

Figure 475-3-9. A- or AthwartshipCoil.

S9086-QN-STM-010/CH-475

3-5

475-3.7.1 A-COIL PURPOSE. Thepurpose of the A-coil is to produce a mag-netic field that will counteract the magneticfield produced by the permanent and in-duced athwartship magnetization. Sincethe induced athwartship magnetizationchanges when the ship changes its headingor magnetic latitude, the A-coil fieldstrength must be changed accordingly.When compensation for roll is required, theA-coil field strength must also be changedas the ship rolls.

475-3.8 P-COIL

The P- or permanent coil, used on minewarfare vessels, consists of conductors inthe M-, A-, and L-coil cables connected inseries to form the P-coil. The P-coil com-pensates for the permanent vertical, ath-wartship, and longitudinal magnetization.Since the permanent magnetization doesnot change when the ship changes its head-ing or latitude, no change in P-coil fieldstrength is needed.

475-3.9 AUXILIARY COILS (MX, AX,LX, PX)

Auxiliary coils are used on some nonmag-netic minesweepers to provide greater ad-justment capability during calibration ofcoil installations at a magnetic range (seesection 6).

475-3.10 NUMBER OF COILS USED

Different combinations of the degaussingcoils are installed aboard different ships.The combination selected for a particularship will depend on the ship’s size and in-tended service. The most common combina-tions used are:

M, FI-QI, FP-QPM, FI-QI, FP-QP, AM, L, A, PM, L, A, P, MX, LX, AX, PX.

475-3.11 COIL FIELD STRENGTH

The magnetic field produced by a degauss-ing coil is proportional to ampere turns,designated as NI (the product of the num-ber of turns in the coil times the coil currentin amperes). A specified number of ampereturns can be obtained by using one turnand a current numerically equal to the re-quired ampere turns, or by using moreturns and a correspondingly smaller cur-rent. The magnetic field near degaussingcables can be estimated using the followingformula:

H = 0.00667NI ÷ D

where:

H = the magnetic field intensityin oersteds

NI = the total ampere-turns ofthe degaussing cables

D = the distance in feet fromthe cable to the point

475-3.11.1 METHODS TO CHANGECOIL FIELD STRENGTH. Fieldstrengths of all degaussing coils, except thepermanent coils, must be changed when theship changes its magnetic latitude. In ad-dition, coil field strengths of the F-, Q-, FI-QI, L- and A-coils must be changed whenthe ship changes its heading. When com-pensation for pitch and roll is required: theM-coil field strength must be changed whenthe ship pitches or rolls; the L-, F-, Q- or FI-QI coil field strength must be changed whenthe ship pitches; and the A-coil fieldstrength must be changed when the shiprolls. Coil field strength is changed bychanging the ampere turns. This can bedone by changing the current while keepingthe turns constant, changing the turnswhile maintaining the current constant or,changing both the current and the turns.Changing the coil current is the only

S9086-QN-STM-010/CH-475

3-6

method now used for new construction. Insome previous installations still in use, thesecond and third methods are used.

475-3.12 SINGLE CONDUCTORAND MULTICONDUCTORCOILS

Degaussing coils may be made with eithersingle conductor or multiconductor cables.

475-3.12.1 SINGLE-CONDUCTORCOILS. Coils with single conductorcables have only one turn or a small num-ber of turns. They can carry a current onthe order of hundreds of amperes at low vol-tages, about 10 to 65 volts. Single conduc-tor cables or a combination of some singleconductor and some multiconductor cablesare usually specified for the M-, F-, Q-, andA-coils used on large ships.

475-3.12.2 MULTICONDUCTORCOILS. When multiconductor cablesare used for degaussing coils, the conduc-tors in one or more cables are connected inseries to give a considerable number ofturns. The current in each conductor canbe on the order of tens of amperes at vol-tages of about 120 to 250 volts. Multicon-ductor cables for degaussing coils areusually specified for the high-voltage, low-current systems employed on smaller shipsor for the FI-QI and FP-QP coils used onlarge ships.

475-3.13 DEGAUSSING COILPOLARITY, MARKINGAND DESIGNATION

475-3.13.1 DIRECTION OFELECTRIC CURRENT. The direc-tion of electric current in a conductor loopconnected to a battery is from the positiveterminal to the negative terminal. Therelation between the direction of the cur-

rent and the direction of the magnetic linesof force around the conductor is shown infigures 475-3-1 and 475-3-2.

475-3.13.1.1 Degaussing PolarityIndicators. The direction of current ina degaussing coil can be checked by usingeither a degaussing polarity indicator (suchas H6625-00-314-4162) or a small handcompass. The polarity indicator dial ismarked to show the direction of current.Compass deflections that correspond topositive degaussing coil currents are givenin paragraphs 475-3.13.2 through475-3.13.2.5.

475-3.13.1.2 Polarity IndicatorPrecautions. To avoid reversing theneedle in the polarity indicator or compass,neither one should be brought too close todegaussing cables. Whichever one is usedshould be moved toward the cables only un-til a good deflection is obtained, and nocloser. In addition, the indicator or com-pass should be checked after each test tomake sure the needle has not reversed.

475-3.13.2 COIL POLARITY. InM-, F-, Q-, FI-, FP-, QI-, and QP-coils, thedirection of positive current is forward onthe starboard side (counterclockwise asviewed from above the coil). A small com-pass held above the degaussing cable willpoint outboard for a positive current in thecoil.

475-3.13.2.1 A Coil PolarityConvention. In the A-coil, the direc-tion of the positive current is aft in the up-per run (counterclockwise as viewed fromthe starboard side). A small compass heldbelow the upper run of the A-coil will pointto starboard for positive current in the coil.

S9086-QN-STM-010/CH-475

3-7

475-3.13.2.2 L-Coil PolarityConvention. In the L-coil, the direc-tion of positive current is upward on thestarboard side (counterclockwise as viewedfrom the after side of the coil). A smallcompass held below the upper run where itcrosses athwartships will point aft for posi-tive current in the coil.

475-3.13.2.3 FI and QI Coil LoopPolarity Convention. The FI andQI loops of an FI-QI coil are connected inseries so that when the current is positivein the FI loops it is negative in the QI loops.The polarity of the FI-QI coil is the same asthe polarity of the FI loops; that is, the am-meter for the FI-QI coil indicates positivecurrent when the FI loops are positive.

475-3.13.2.4 FP and QP Coil LoopPolarity Conventions. The FP andQP loops of an FP-QP coil on a new instal-lation are connected in series, so that whencurrent is positive in the FP loops, it isnegative in the QP loops. If ranging theship (section 6) shows that it is desirable tohave the FP and QP loops connected toproduce fields in the same direction, theyshould then be reconnected. The polarity ofthe FP-QP coil is the same as the polarity ofthe FP loops; that is, the ammeter for theFP-QP coil indicates positive current whenthe FP loops are positive.

475-3.13.2.5 Ammeter DeflectionConvention. The pointer of a zerocenter ammeter will deflect to the right forpositive current in the coil with which theammeter is used.

475-3.13.3 MARKING. The letters tobe used for designating and markingdegaussing installations and their mean-ings are shown in table 475-3-1.

475-3.13.4 LOOP DESIGNATION.Each degaussing coil may consist of one ormore loops. Each loop may consist of one ormore turns of cable.

a. The number 1, when used with theM-, F- or Q-coil (M1, F1, Q1); or the FI, FP,QI, or QP loops of the FI-QI or FP-QP coils,designates the longest loop. Other loops ineach coil shall be numbered in sequence 2,3, 4, and so on from bow to stern (seefigures 475-3-10 and 475-3-11).

Figure 475-3-10. Numbering M-CoilLoops.

Figure 475-3-11. Numbering F- andQ-Coil Loops.

b. The number 1, when used with theL-coil (L1), designates the forward loop.Other loops are designated L2, L3, L4, andso on, in sequence, from bow to stern.

S9086-QN-STM-010/CH-475

3-8

c. When used with the A-coil (A1, A2),the numbers 1 and 2 designate the star-board and port longest loops, respectively,with other loops following in sequence frombow to stern.

d. For minesweepers, the M1 loop doesnot go around the ship. All loops (M, A andL) are numbered consecutively from bow tostern except for loop pairs at the same dis-tance from the bow. Loop pairs are num-bered as follows:

1. Odd loop numbers are used for up-per or starboard loops.

2. Even loop numbers are used forlower or port loops.

475-3.13.5 CIRCUITDESIGNATION. Consider a degauss-ing coil loop consisting of one turn of four-conductor cable. Although degaussingcables have either only one conductor ormore than four, a four-conductor cableserves to illustrate the meaning to be at-tached to circuits.

475-3.13.5.1 Circuits of Four-turnLoops. The four conductors in thecable may be connected as shown in figure475-3-12. In this case there is only one cir-cuit. Alternatively, the four conductors inthe cable may be connected as shown infigure 475-3-13. In this case there are twocircuits. The first and second turns inseries are in parallel with the third andfourth turns in series.

475-3.13.5.2 Conductor CircuitDesignation. The letters A, B, C, andso on are used as indicated in paragraph475-3.13.9.1 to designate the circuit inwhich a particular conductor is connected.

475-3.13.6 COIL CABLEDESIGNATION. Degaussing coilcables are marked with: a D for degauss-

Figure 475-3-12. M-Coil With a SingleCircuit.

Figure 475-3-13. M-Coil With TwoParallel Circuits.

ing, a dash, a number (1, 2, 3) to indicatethe particular cable in a coil, the ap-propriate letter for the degaussing coildesignation (M, F, Q, FI, FP, QI, QP), asecond dash, and a number to indicate theparticular section of the cable. Thus,D-2M-1 stands for the number 1 section ofthe number 2 cable of the M-coil. A sectionof a degaussing coil cable is the length ofcable between two successive connections orthrough boxes. The number designation fora cable is to be retained throughout one

S9086-QN-STM-010/CH-475

3-9

TABLE 475-3-1. DEGAUSSING INSTALLATION MARKING

A Athwartships coil

AMM Ammeter

AP A coil to correct for permanent magnetism

AX A-auxiliary coil

CC Compass compensating coil

D Degaussing system

F Forecastle coil to correct for both permanent and in-duced magnetism

FDR Feeder

FI F-coil to correct for induced magnetism

FP F-coil to correct for permanent magnetism

I FI-QI coil - used in conjunction with feeders, compasscompensating coil, and indicator light leads

IL Indicator light

L Longitudinal coil

LP L-coil to correct for permanent magnetism

LX L-auxiliary coil

M Main coil

MP M-coil to correct for permanent magnetism

MX M-auxiliary coil

P Used in conjunction with feeders for AP, FP-QP, LP andMP coils

PX P-auxiliary coil

Q Quarterdeck coil to correct for both permanent and in-duced magnetism

QI Q-coil to correct for induced magnetism

QP Q-coil to correct for permanent magnetism

SPR Spare conductor

complete turn in a coil or loop if the cablemakes a complete turn, or for as far as thecable goes if it does not make a completeturn. Therefore, while the number desig-nation for a cable does not change when thecable goes through an intermediate connec-tion or through box, the number desig-

nation for a section does. Section numbersare assigned as follows:

a. For a cable in a horizontal coil, sec-tion number 1 is assigned to the sectionthat is farthest forward. The remainingsections are marked in sequence goingaround the coil counterclockwise as viewedfrom above.

S9086-QN-STM-010/CH-475

3-10

b. For a cable in the A-coil, section 1 isassigned to the section that is highest andfarthest forward. The remaining sectionsare numbered in sequence going around thecoil counterclockwise as viewed from thestarboard side.

c. For a cable in the L-coil, section 1 isassigned to the section that is highest andfarthest forward. The remaining cable sec-tions are numbered in sequence goingaround each loop counterclockwise asviewed from the after side of the loop andgoing from loop to loop fore to aft.

475-3.13.6.1 Degaussing Coil CableSection Number. The section num-ber should always be included in a degauss-ing coil cable designation even if the cablehas only one section. See figure 475-3-14for examples of degaussing coil cable desig-nations.

475-3.13.7 FEEDER CABLEDESIGNATION. Cable designationsvary with cable use.

475-3.13.7.1 Power Supply Cables.Degaussing power supply feeder cables aremarked with a D for degaussing, a dash,FDR for feeder, a letter to indicate the coilto which the feeder carries current, asecond dash, and a section number. A sec-tion in a feeder cable is the length of cablebetween two successive items of equipment.Sections should be numbered in sequencestarting from the degaussing panel, asD-FDRI-1, D-FDRI-2, and so on, if there areseveral sections, or D-FDRI-1 if there isonly a single section. When two or morefeeder cables run to a coil, they should benumbered as indicated for degaussing coils.For example, D-1FDRM-1 and D-2FDRM-1for two feeder cables to the M-coil (figure475-3-16). When single-conductor cablesare used as feeder cables, the cable with thepositive conductor should be numbered 1;the cable with the negative conductor

should be numbered 2. If more than twosingle-conductor cables are used for thefeeders to one coil, odd numbers should beused for the feeders with positive conduc-tors.

475-3.13.7.2 InterconnectingCables. Interconnecting cables be-tween FI and QI loops or FP and QP loopsare considered feeder cables and bear thedesignation of the loop to which they carrypower. For example, the feeder cable thatcarries power from the degaussing panel tothe FI-QI coil is designated D-FDRI-1, D-FDRI-2, and so on, regardless of whether itconnects to the FI loop or the QI loop. If thefeeder cable for the FI-QI coil connects tothe FI loop, the interconnecting cable be-tween the FI and QI loops carries powerfrom the FI to QI loop and is designatedD-FDRQI-1 as illustrated infigure 475-3-14. If, on the other hand, thefeeder from the degaussing panel connectsto the QI loop, the interconnecting cable be-tween the FI and QI loops carries powerfrom the QI to the FI loop and is designatedD-FDRFI-1.

475-3.13.7.3 Compass CompensatingCoil and Indicator Light Cables.Feeder cables for compass compensatingcoils, ammeters, or indicator lights shouldbe designated D-FDR followed by a dashand letters to indicate the equipment towhich they are connected: for example,D-FDRM-CC for an M-coil compass coilfeeder. Section numbers are omitted (seefigure 475-3-16 for examples).

475-3.13.8 OTHER CABLEDESIGNATION. All feeders, mains,and other cables supplying power todegaussing switchboards, power supplies,and control panels shall be designated andmarked as specified for power and lightingcircuits in accordance with NSTMChapter 300, Electric Plant General.

S9086-QN-STM-010/CH-475

3-11

Figure 475-3-14. Degaussing Coil Cable Designations, Typical.

S9086-QN-STM-010/CH-475

3-12

475-3.13.9 CONDUCTORDESIGNATION. Both the cable desig-nation given in paragraphs 475-3.13.6through 475-3.13.8, and the conductordesignation given in paragraphs475-3.13.9.1 and 475-3.13.9.4, should beused even when the cable has only one con-ductor. This is because the conductor desig-nation gives some information that thecable designation does not.

475-3.13.9.1 Single Conductors.Single conductors are to be marked by hotstamping (branding) the insulating sleev-ing, MIL-I-631, type F, grade A, form U(white) of appropriate size. The conductormarking shall conform with that of the ter-minal to which it connects. The followingsymbols, as applicable, should be used, ar-ranged in the order given:

a. M, F, Q, FI, FP, QI, QP, A, and so on- degaussing coil.

b. 1, 2, 3, and so on - degaussing coilloop number (see paragraph 475-3.13.4).Omit the number if the coil has only oneloop.

c. A, B, C, and so on - first, second,third parallel circuit in the coil (seeparagraph 475-3.13.5). Use A if there isonly one circuit.

d. 1, 2, 3, and so on - first, second, thirdseries conductor in a circuit. A conductorthat is connected in a degaussing coil orloop makes a complete turn and retains thesame number designation throughout theentire turn.

e. Plus (+) or minus (-), shown on theconductor, as indicated in paragraph475-3.13.9.4.

475-3.13.9.2 Spare Conductors.Spare conductors are marked with hotstamped plastic insulating sleeving withthe same designations as the other conduc-tors, except as follows:

a. For a spare conductor that is avail-able for a complete turn, omit the circuitdesignation A, B, C, and so on, and sub-stitute SPR in its place.

b. For a spare conductor that is notavailable for a complete turn, use the desig-nation of the cable in which the spare con-ductor is contained, including the cable sec-tion number, and follow the cable desig-nation with SPR, a number to identify thespare conductor, and + or - to indicategeometric polarity (for example,D-3M-1SPR2+).

475-3.13.9.3 Parallel Conductors.Conductors paralleled together within aportion of a particular series or parallel cir-cuit and not constituting regular full-lengthcircuits, receive the same conductor desig-nation that equivalent single conductorswould receive (see figure 475-3-15 for ex-ample).

475-3.13.9.4 Positive and NegativeGeometric Polarity. Positive andnegative geometric polarity is as follows:

a. The ends of M, F, Q, FI, FP, QI andQP coil conductors approaching a box(paragraphs 475-3.13.13 through475-3.13.15) in the counterclockwise direc-tion, as observed from above the coil (for ex-ample, from aft for a box on the starboardside), will be positive.

b. The ends of A-coil conductors ap-proaching a box counterclockwise, asviewed from the starboard side of the coil(for example, from aft for a box in the lowerrun of the coil), will be positive.

c. The ends of L-coil conductors ap-proaching a box counterclockwise, as seenfrom the after side of the coil (for example,from below a box on the starboard side),will be positive.

d. The conventions used for geometricpolarity, positive direction of current

S9086-QN-STM-010/CH-475

3-13

Figure 475-3-15. Typical M-Coil Connection Box.

S9086-QN-STM-010/CH-475

3-14

(paragraphs 475-3.13.1 through475-3.13.1.2) and positive direction of cur-rents in degaussing coils (paragraphs475-3.13.2 through 475-3.13.2.5), are so re-lated that when the current in a degaussingcoil and ammeter is negative, the electricaland the geometric polarities of loop conduc-tor ends are the same.

475-3.13.10 FEEDER CABLE CON-DUCTOR DESIGNATION. Feedercable conductors are designated in a dif-ferent manner than the degaussing coiltype. There are two types of feeder cableconductors.

475-3.13.10.1 Power SupplyCables. Conductors to degaussing coilsare designated by the following symbols, asapplicable, in the order given:

a. FDR: feeder.

b. M, F, Q, FI, and so on: degaussingcoil.

c. 1, 2, 3, and so on: coil loop number.The loop number is omitted if the coil hasonly one loop.

d. A, B, C: circuit designation. Usedonly when individual parallel circuits arefed separately. For example, where mul-ticircuit rheostats are used.

e. Plus (+) and minus (-): positive andnegative electric polarity when the controlsare in the position for positive current (seeparagraph 475-3.13.2 through 475-3.13.2.5).Feeder cable conductors carry the samepolarity designation for the entire length ofthe conductor.

475-3.13.10.2 Compass Compen-sation and Indicator Light Cables.Conductors in compass compensating and

indicator light feeder cables are designatedwith the following symbols in the ordergiven:

a. M, F, Q, I, P, A, L, and so on:degaussing coil.

b. CC: for compass compensating coilconductors; or, IL: indicator light conduc-tors.

c. Plus (+) and minus (-): electricpolarity when the current in the coil is posi-tive (see figure 475-3-16 for examples).

475-3.13.11 CABLE AND CONDUC-TOR TAGS, NAVAL SHIPS. Cableand conductor tags on Naval ships shouldconform to NSTM Chapter 300, ElectricPlant General, and paragraphs475-3.13.9.1 through 475-3.13.9.3. Tagsand marking are to be rigidly attached tothe cable or conductor so that the tag mark-ing is parallel to the axis of the cable or theconductor.

475-3.13.12 CABLE AND CONDUC-TOR TAGS, MERCHANT SHIPS.Cable and conductor markings for merchantships are the same as for Naval ships. Inboth Naval and merchant ships, a degauss-ing coil conductor marking is to be fastenedto each end of a conductor inside the con-nection or through box.

475-3.13.13 CONNECTION ANDTHROUGH BOXES.

475-3.13.13.1 Definitions - Connec-tion Box. A connection box is a water-tight box used to connect loops together, toconnect conductors in series, to reverseturns, etc. The power supply connection fora coil and all adjustments of ampere turnratios between loops are made within con-nection boxes. The power supply cable andinterconnecting cable for the FI-QI andFP-QP coils terminate at connection boxes.

S9086-QN-STM-010/CH-475

3-15

Figure 475-3-16. Feeder Cable Conductor Designation.

S9086-QN-STM-010/CH-475

3-16

475-3.13.13.2 Definition - ThroughBox. A through box is a watertight boxused to connect conductors together withoutchanging the order of conductor connection.It is used when it is necessary to connectsections of cable together. In some casessplicing instead of through boxes is used.

475-3.13.13.3 Numbering.Connection and through boxes in the M,MX, F, Q, FI-QI and FP-QP coils are con-sidered to be in one group. They are num-bered D1, D2, D3, and so on, in sequence,starting at the bow and going around theship counterclockwise as observed fromabove (figure 475-3-14).

475-3.13.13.4 A-Coil and BoxNumbering. Boxes for the A-coilreceive the next higher numbers after num-bers for the M, F, FI, FP, QI and QP boxeshave been assigned. Numbers for the A-coilboxes are in sequence starting with thehighest forward box and continuing aft onthe upper limbs of both the A1 and A2loops, then down to the forward on thelower limbs, and then up (figure 475-3-14).

475-3.13.13.5 L-Coil and BoxNumbering. Boxes for the L-coilreceive the next higher numbers after num-bers for the A-coil boxes have been as-signed. Numbers for the L-coil boxes areassigned in sequence starting with thehighest forward box on the port side andcontinuing around the ship in a coun-terclockwise direction as viewed fromabove. Boxes on the centerline are con-sidered to be on the port side for number as-signment.

475-3.13.14 IDENTIFICATIONPLATES. Connection and throughboxes should have identification platesmarked as follows:

a. Degaussing box number - D1, D2,D3, and so on

b. Connection box or through box, asapplicable

c. Coil and loop designation - M1, M2,FI1, QI1, and so on.

EXAMPLE:

D1

CONNECTION BOX THROUGH BOX

M1 FI1

M2

NOTE

This example identifies theNo. 1 degaussing box serv-ing as a connection box forthe M1 and M2 loops and asa through box for the FI1loop.

475-3.13.15 WIRING DIAGRAM. Awiring diagram of the connection within abox should be pasted on the inside of thebox cover and coated with varnish or shel-lac. The wiring diagram for connectionboxes should designate the conductors thatmay be reversed without reversing otherloops, should indicate the arrangement ofparallel circuits so that equal changes canbe made in all parallel circuits when suchchanges are required, and should also showspare conductors. Spare conductors shallbe secured to connection terminals in theconnection boxes and shall not form aclosed-loop circuit. All conductors within aconnection box shall be cut to allow 1-1/2times the length required to reach the far-thest terminal within the box. The wiringdiagram should show the direction of posi-tive loop current and should include the fol-lowing warning note:

S9086-QN-STM-010/CH-475

3-17

WARNING

Important for magneticdefense: To maintain theship’s magnetic signatureensure that the connectedturns for each loop in thisbox are in accordance withthe turns specified in theship’s degaussing folder.Use this original connectionwiring diagram (insidecover) for general guidanceonly.

475-3.14 REQUIRED COIL CUR-RENT ALGORITHM

Degaussing coils are installed so that theyproduce compensating fields parallel toeach of the ship’s three axes to counteractthe permanent and induced magnetizationalong each of these axes (see paragraphs475-3.1 through 475-3.2). Coil fieldstrength is a function of coil current (seeparagraph 475-3.11), and required coil fieldstrength is a function of the inducing fieldand the permanent magnetization. Re-quired coil current is therefore a function ofthe magnitude and polarity of the earth’smagnetic field and the component of per-manent magnetization, along the axis of theship. This is illustrated by the followingformula:

I = Kφ + Ip

where:

I = required coil current

φ = component of earth’s magneticfield along ship’s axis

Ip = current required to compensatefor permanent magnetization

K = gain constant determinedduring calibration.

The first term in the equation, Kφ,represents the current component for com-pensating the ship’s induced field (inducedfield current) and the second term, Ip,represents the current component for com-pensating the ship’s permanent field (permfield current). The magnitude and polarityof Ip is constant and the same values areused until the ship is recalibrated. Themagnitude and polarity of φ is obtained byone of two methods:

a. Measuring φ with a magnetometer.

b. Calculating φ as a function of the fol-lowing parameters:

φ = f (H, Z, a, r, p)

where:

H = the horizontal component ofthe earth’s magnetic field(see paragraphs 475-2.1through 475-2.1.3.2)

Z = the vertical component ofthe earth’s magnetic field(see paragraphs 475-2.1through 475-2.1.3.2)

a = ship’s magnetic heading

r = ship’s roll angle

p = ship’s pitch angle.

S9086-QN-STM-010/CH-475

3-18

S9086-QN-STM-010/CH-475

4-1

SECTION 4. DEGAUSSING CONTROL EQUIPMENT

475-4.1 OPERATOR CURRENTCONTROL - PRIOR TOMID-1950S EQUIPMENT

Many of the older (prior to the mid-1950s)three-coil degaussing installations and allinstallations with only an M-coil, haveoperator current control. These instal-lations were fabricated and installed by theshipbuilders. They were never assignedtype designations. Manual or operator con-trol is necessary because an operator mustadjust the degaussing coil currents whenthey have to be changed because of achange in the ship’s heading or magneticlatitude, or both. In such installations, rolland pitch compensation is not provided.

475-4.2 MANUAL CURRENT AD-JUSTMENT EQUIPMENT

This equipment controls power obtainedfrom constant voltage dc generators in someinstallations and from degaussing motorgenerators in other installations. Coil cur-rents are set by adjusting rheostats. Therheostats are in series with the degaussingcoils when the power is obtained from aconstant voltage source, and in series withthe generator field when motor-generatorsare used for the power source. Bothmanually operated and motor-driven rheos-tats are used. The required coil currents foreach of the ship’s degaussing coils, thevarious magnetic latitudes, and the majorship’s headings are obtained from thedegaussing charts in the ship’s degaussingfolder. These current values are deter-mined for one latitude and calculated forother latitudes during calibration ranging.The current values given in the degaussingfolder for the various zones of operationrepresent the sum of the induced field andperm field currents.

475-4.3 AUTOMATIC CURRENTCONTROL EQUIPMENT

Automatic degaussing (AUTODEG) controlequipment is equipment that adjusts someor all the coil currents automatically withchanges in the ship’s attitude (heading, roll,pitch, trim, list) or with changes in both theattitude and location. This type of controlequipment is provided on all ships withdegaussing coils installed in more than oneplane. The two basic types of AUTODEGcontrol equipment currently provided are:

a. Magnetometer-controlled equipment

b. Gyro-controlled equipment.

475-4.3.1 MAGNETOMETERCONTROL. Signals to control the in-duced field currents are obtained from athree-axis magnetometer. The mag-netometer measures the components of theearth’s field along the axes of the ship andautomatically adjusts the coil currents in amanner that will compensate for changes inthe induced magnetization caused by theship’s roll and pitch and by changes in theship’s heading and geographical location.The perm field current is obtained by bias-ing the magnetometer output with a permbias component or by providing a P-coilwith a separate regulated current source(see paragraph 475-3.8) or a combination ofboth methods.

475-4.3.1.1 Magnetometer Controlon Nonmagnetic Minesweepers.Magnetometer control is used on nonmag-netic minesweepers because roll and pitchcompensation and smooth or stepless zonecontrol (magnetic latitude variations) areneeded for these ships. It is also used onminesweepers because the magnetometercan be readily located so that it measuresthe earth’s field rather than a combination

S9086-QN-STM-010/CH-475

4-2

of the earth’s field, ship’s field and other in-terference fields.

475-4.3.1.2 Magnetometer Controlon Special Steel Hull Ships.Magnetometer control is also used on somesteel hull ships with aluminum superstruc-tures where the effect of the ship’s field onthe magnetometer can be cancelled by com-pensation techniques. Magnetometer con-trol is used on these ships to eliminate theoperator inputs (H, Z, and magnetic varia-tion) required with gyro-controlled equip-ment.

475-4.3.2 GYRO CONTROL.Signals to control the induced field are ob-tained from the ship’s gyro compass andgyro stabilizer systems.

475-4.3.2.1 Gyro Control - InducedField. Signals are modified by operatorinputs for magnetic latitude and heading(operator sets the H-zone, Z-zone and mag-netic variation controls), and processed byan analog computer to provide induced fieldcompensation currents proportional to thecalculated values of φ.

475-4.3.2.2 Gyro Control - PermField. The perm field current is ob-tained by biasing computer output, or witha separate P-coil, or with a combination ofboth methods. Gyro control is currentlyused on ships that do not require roll andpitch compensation. On these ships thecontrol signal is obtained from the ship’sgyro compass, and the coil currents are ad-justed automatically to compensate only forthe change in the induced magnetizationcaused by a change in the ship’s heading.

475-4.3.3 EMERGENCY MANUALCONTROL. All types of AUTODEGcontrol equipment are equipped with emer-gency manual controls for use if the

automatic controls become inoperative.This equipment is manually operated bysetting currents to values obtained from theship’s degaussing folder for the variousmagnetic latitudes and adjusting the eight-course heading switch as the ship’s headingvaries.

475-4.4 EQUIPMENT DESCRIP-TION

Brief descriptions of the different types ofautomatic degaussing equipment are givenin table 475-4-1. Detailed descriptions forspecific equipment are given in the tech-nical manuals for each type of equipment.The first three types - MDG, SSM and MCD- are the only types being installed on newships. These types are further described inparagraphs 475-4.4.1 through 475-4.4.3.

475-4.4.1 TYPE MDG. Type MDGdegaussing equipment is installed on non-magnetic minesweepers. This equipmentconsists of a fluxgate-type triaxial mag-netometer probe installed on the ship’smast and a control unit, containing all con-trol and power circuits, installed in Com-mand Information Center (CIC) or the pilothouse (figure 475-4-1). The magnetometerprobe is located and aligned so that itmeasures the earth’s local magnetic fieldcomponents along each of the ship’s threeaxes. These field components are biasedand amplified by the degaussing equipmentto produce the required degaussing coil cur-rents (figure 475-4-2). The probe locationmust be free of interference produced by theship’s magnetic field, degaussing coils andother installed equipment. The equipmentis unique in that ninety separate poweramplifiers are available to supply the ship’sdegaussing loops.

475-4.4.2 TYPE SSMEQUIPMENT. Type SSM degaussingequipment is the standard degaussingequipment installed on all ships that re-

S9086-QN-STM-010/CH-475

4-3

TABLE 475-4-1. AUTODEG EQUIPMENT

Equipmenttype codes Description

MDG Control signals from three-axis magnetometer. Solid-state control circuits with as many as ninety poweramplifiers available to supply the degaussing loops.

SSM Control signal from heading gyro. Solid-state controlcircuits. Silicon-controlled rectifier-type power supplies.

MCD Control signals from magnetometer. Solid-state controlcircuits. Silicon-controlled rectified-type power sup-plies.

GEM Control signal from three-axis magnetometer. Com-bination of solid-state and magnetic amplifier controlcircuits. Controls field of degaussing motor generator.This equipment is type GM equipment that has beenconverted to magnetometer control.

SEM Control signal from three-axis magnetometer. Com-bination of solid-state and magnetic amplifier-typepower supplies.

GM Control signal from heading gyro or from heading gyroand gyro stabilizer. Magnetic amplifier control circuits.Controls field of generator of degaussing motor gener-ator.Note: All type GM equipment with roll and pitch sig-nals from the gyro stabilizer have been converted totype GEM equipment.

FM Control signal from heading gyro. Magnetic amplifiercontrol circuits. Controls field of exciter of degaussingmotor generator.

RM Control signal from heading gyro. Magnetic amplifiercontrol circuits. Controls motor of motor-driven rheos-tat. Rheostat is in series with degaussing coil connectedto constant voltage dc power supply.

EMS Control signals from three-axis magnetometer. Solid-state control circuits. Power transistors or silicon-controlled rectifiers for power control.

quire degaussing except nonmagneticminesweepers and patrol frigates (FFG 7class). This equipment consists of a controlswitchboard, remote control unit and apower supply for each installed degaussingcoil (figure 475-4-3).

475-4.4.2.1 SSM Control EquipmentDescription. The switchboard con-tains all operator controls, control circuitsand status indicators for all coils. Theswitchboard is functionally divided tofacilitate operation and maintenance. Theremote control unit provides status in-dicators and a heading switch for emer-

S9086-QN-STM-010/CH-475

4-4

Figure 475-4-1. Type MDG Automatic Degaussing Equipment.

S9086-Q

N-S

TM

-010/CH

-475

4-5

Figure 475-4-2. Block Diagram for Type MDG Degaussing System.

S9086-QN-STM-010/CH-475

4-6

Figure 475-4-3. Type SSM Automatic Degaussing Equipment.

S9086-QN-STM-010/CH-475

4-7

gency manual operation in a remote loca-tion (usually the pilot house). The com-puter drawer contains an electro-mechanical computer and the controlsnecessary to provide induced FI-QI and A-coil current magnitudes derived from theship’s heading and location (figure 475-4-4).The automatic and manual drawers containcurrent controls, meters and status in-dicators for the automatic coils (FI-QI andA) and the manual coils (M and FP-QP).The ground detector, temperature alarmbell, power-supply blown fuse indicators,and power switches are located on the frontpanels.

475-4.4.2.2 SSM Power ControlEquipment. The power suppliesamplify the control signals from theswitchboard. The power supplies are sup-plied in standard power ratings and differonly in their output current ratings. All arefunctionally identical (figure 475-4-5).

475-4.4.3 TYPE MCD. Type MCDdegaussing equipment is installed on FFG 7class ships. This equipment consists of afluxgate-type triaxial magnetometer, con-trol unit, remote control unit, and powersupply unit for each installed degaussingcoil. It is essentially a combination of typeEMS equipment and type SSM equipment.The magnetometer and control unit arefunctionally similar to the type EMS mag-netometer and control unit. The main dif-ferences are that additional compensationfeatures are provided to minimize the effectof the ship’s magnetic field at the mag-netometer and the control unit outputs arecurrent signals to the power supplies in-stead of currents to the degaussing coils.The remote control unit and the power sup-plies are similar to the type SSM remotecontrol unit and power supplies.

475-4.5 DEGAUSSING EQUIPMENTOPERATION, GENERAL

General information on operatingautomatic degaussing equipment is given inparagraphs 475-4.5.2 through 475-4.5.3.5.However, technical manuals are furnishedwith all AUTODEG control equipment andthese manuals should be consulted fordetailed operation information. Technicalmanuals were not furnished with older,operator control-type equipment. Infor-mation on operating this equipment isprovided in the ship’s degaussing folder andparagraph 475-4.5.3.5.

475-4.5.1 ESSENTIAL POINTS.The essential points in degaussing equip-ment operation are:

a. Energize the degaussing equipmentin accordance with the instructions fur-nished with the equipment.

b. Set and maintain the coil currents tothe values specified in the ship’s degaussingfolder.

c. Periodically monitor the trouble in-dicators and coil currents for indications ofequipment malfunctions.

475-4.5.2 MAGNETOMETER-CONTROLLED AUTODEG EQUIP-MENT OPERATION. Two modes ofoperation are used for magnetometer-controlled AUTODEG equipment.

475-4.5.2.1 Automatic Operation.Magnetometer-controlled equipment, whenset up for automatic operation, will controlthe currents in the ship’s degaussing coilsin a manner that will compensate for theship’s permanent and induced magnetismregardless of the ship’s heading, roll, pitchor geographic location. Automatic opera-tion is the normal mode and consistsprimarily of turning the equipment on andperiodically monitoring the front panel in-

S9086-QN-STM-010/CH-475

4-8

Figure 475-4-4. Block Diagram for Type SSM Degaussing Switchboard.

Figure 475-4-5. Block Diagram for Type SSM Degaussing Power Supply.

dicators and current outputs for indicationsof equipment malfunction.

475-4.5.2.2 Automatic PerformanceChecks. During calibration of thedegaussing system at a degaussing range,the coil turns, current magnitude and cur-rent polarities are established. When

S9086-QN-STM-010/CH-475

4-9

calibration is completed, the coils are con-nected for proper turns, the equipment isadjusted for automatic operation, and allpertinent information is recorded in theship’s degaussing folder. During normal(automatic) operation, none of the controlsare adjusted or reset. Trouble indicatorsshould be monitored periodically. Currentoutputs should be checked as follows:

a. The magnitude and polarity of per-manent coil (FP-QP and P-coils) currentsshould be measured and compared with thevalues specified in the ship’s degaussingfolder.

b. Magnetometer outputs should bechecked by comparing the indicated fieldstrength for each axis with the values givenin the ship’s degaussing folder for the ship’sposition. Measurements should be madewith the ship on cardinal magnetic head-ings with little roll and pitch. This proce-dure will provide, at best, a rough check ofthe magnetometer outputs because the in-dicated field strengths are affected by theroll, pitch, trim, and list of the ship. Also,only approximate values of the earth’s localfield can be obtained from charts in thedegaussing folder.

c. The coil (M, A, L, FI-QI coils) cur-rents for induced magnetic compensationshould be measured and compared with theindicated field strengths. The magnitude ofthese currents should be directly propor-tional to the field strength indicated, the in-duced magnitude control setting, and theperm current setting (paragraph 475-3.14).Charts in the degaussing folder provide coilcurrents versus indicated field strengths forinduced compensation coils on cardinalheadings. The adjustment of induced mag-nitude and perm current control settingscan be checked by comparing the currentversus field strength values specified on thechart with the current versus field strengthvalues measured.

475-4.5.2.3 Manual Operation.Magnetometer-controlled equipment pro-vides for operator control of degaussing coilcurrents when a fault exists in the mag-netometer group circuits. Adjustments as-sociated with the ship’s heading and theearth’s local field (H- and Z-zone of opera-tion) are made during manual operation.Since the operator-set heading and theearth’s field inputs only approximate op-timum inputs, and since no roll or pitch in-puts are provided, compensation of theship’s induced magnetism with manualoperation is not as good as the compen-sation obtained with automatic operation.For this reason, when automatic operationis not possible, only the affected coil or coilsshould be operated manually. The generalprocedure for manual operation is:

a. Set the eight-course heading switchfor the ship’s magnetic heading (not re-quired for manual operation of M-coil).

b. Set the M-coil polarity switch for thepolarity specified in the ship’s degaussingfolder (positive for northern latitudes).

c. Set the operational mode switch formanual operation.

d. Check the coil current magnitudeand adjust the manual current control, ifrequired (see CAUTION below), for the cur-rent specified in the degaussing folder forthe ship’s zone of operation.

e. Keep the heading switch set to theposition corresponding to the ship’s mag-netic heading and the coil current mag-nitude adjusted for proper H- or Z-zone ofoperation.

S9086-QN-STM-010/CH-475

4-10

CAUTION

Setting the heading switchto positions other than thepositions corresponding tothe ship’s magnetic headingcan result in degaussingcoil currents with thewrong magnitude or wrongpolarity, which can be dan-gerous in a magnetic minedanger area. Current mag-nitudes should be adjustedin mine danger areas with-out changing the headingswitch position. The proce-dure follows:

f. Adjust the manual induced mag-nitude controls as follows:

1. M-COIL. Adjust the control to ob-tain the current specified for the new loca-tion on the degaussing chart (see the ship’sdegaussing folder).

2. A-COIL. If the heading switch isset in the E or W position, adjust the con-trol to obtain the current specified for thenew location on the degaussing chart. Ifthe switch is set for an intercardinal head-ing, set the control to obtain 70 percent ofthe current specified for the new location.If the heading switch is set in the N or Sposition, do not adjust the control until theship’s heading changes so that the headingswitch is set to a new position.

3. L-COIL and FI-QI COIL. Mag-nitude control for this coil is adjusted in thesame manner as for the A-coil, except that

adjustments are made with the headingswitch in the N, S, and intercardinal head-ing positions. Current should not be ad-justed when the switch is set to the E or Wheadings.

475-4.5.2.4 Technical Manual Con-sultation for Exact Procedures.Exact procedures vary with the equipmentinstalled. Some types of equipment haveseparate manual current controls whichshould be preset so that they do not have tobe adjusted when coils are switched tomanual operation. On equipment withcommon current controls for automatic andmanual operation, the controls should beadjusted for zero current (maximum CCW)before switching to manual operation. Thetechnical manual furnished with the equip-ment should be consulted for detailed infor-mation on adjusting the currents andoperating equipment.

475-4.5.3 GYRO-CONTROLLEDAUTODEG EQUIPMENTOPERATION. As withmagnetometer-controlled equipment, gyro-controlled AUTODEG equipment has twomodes of operation.

475-4.5.3.1 Automatic Operation.Gyro-controlled equipment, when set up forautomatic operation, will automaticallymake changes in coil currents required be-cause of changes in the ship’s heading.Gyro-controlled equipment will notautomatically make changes in the coil cur-rents necessary when the ship changes itsmagnetic latitude (H-zones).

S9086-QN-STM-010/CH-475

4-11

NOTE

Some equipment wouldautomatically change coilcurrents for changes in theship’s roll and pitch, thusproviding roll and pitchcompensation. The follow-ing description does notpertain to this type ofequipment, which is nowobsolete and has been con-verted to magnetometercontrol or removed fromservice.

475-4.5.3.2 Automatic OperationSetup. Automatic operation is the nor-mal mode of operation and consistsprimarily of energizing the equipment, peri-odic monitoring for indications of malfunc-tion, and adjusting the current controls as aship moves from one H- or Z-zone toanother. Gyro-controlled equipment, likemagnetometer-controlled equipment, iscompletely set up and adjusted in accord-ance with ship’s Degaussing Folder, appen-dix A, when the ship’s degaussing system isinitially calibrated at range. Some controlson this equipment, however, must be seteach time the equipment is energized. Thegeneral procedure for automatic operationis:

a. Set the magnetic variation, H-zone,M-coil polarity, and FP-QP coil polarity con-trols to the settings corresponding to theship’s geographic location as obtained fromthe ship’s degaussing folder.

b. Set the FI-QI and A-coil operationmode switches and test switches forautomatic operation. Energize the equip-ment by turning on all the coil powerswitches.

c. Adjust the M- and FP-QP currentmagnitude controls for the current specified

in the degaussing folder for the ship’s posi-tion.

d. Keep the magnetic variation, H-zone,M-, and FP-QP current polarities and mag-nitudes set for the ship’s geographic loca-tion.

e. Periodically monitor the trouble in-dicators for any indication of malfunction.

475-4.5.3.3 Automatic OperationPerformance Checks. Periodicallymonitor the currents and compare themwith the values specified in the degaussingfolder for the ship’s location. (Refer to thecoil current tables in the ship’s DegaussingFolder.) The magnitude and polarity of FI-QI and A-coil currents will vary with theship’s heading. These should be monitoredon cardinal headings or calculated. The FI-QI current should be equal to the valuespecified for the ship’s location, multipliedby the cosine of the ship’s magnetic headingangle. The A-coil current should be equal tothe value specified for the location, mul-tiplied by the sine of the magnetic headingangle.

475-4.5.3.4 Manual Operation ofGyro-controlled Equipment.Gyro-controlled equipment has a provisionfor operator control of the FI-QI and A-coilcurrents with a loss of gyro signal or a faultin the control computer. Manual operationconsists of keeping the heading switch setfor the ship’s magnetic heading and the H-zone switch set for the ship’s position.Since step inputs from the heading switchonly approximate the heading signals fromthe gyro and control computer, the ship’s in-duced magnetism compensation duringmanual operation is not as good as thatprovided by automatic operation. Con-sequently, the equipment should beoperated manually only when normaloperation is impossible.

S9086-QN-STM-010/CH-475

4-12

475-4.5.3.5 Manual OperationSetup. The equipment should be set upfor manual operation (the manual inducedmagnitude current controls should be ad-justed and locked) at the same time it is setup for automatic operation. This will en-able the operator to switch from automaticto manual operation without having to ad-just the current magnitude because incor-rect current or changes in current mag-nitudes and polarities can be dangerous ina mine danger area. If the reason forswitching to manual operation is defectiveautomatic operation, see "Operating withDefective Equipment" in the instructionsappendix section of the ship’s DegaussingFolder. The general procedure for manualoperation of the FI-QI or A-coil is:

a. Set the local-remote transfer switchfor local operation, the H-zone switch forthe ship’s position and the eight-courseheading switch for the ship’s magneticheading.

b. Set the operational mode switch formanual operation and the power switch toon.

c. Keep the H-zone set for position andthe heading switch set for magnetic head-ing.

d. Periodically monitor the trouble in-dicators and currents for indications of mal-function. The current magnitude andpolarity will depend on the heading switchposition. The magnitude should be zero, 70or 100 percent of the value specified in thedegaussing folder for the ship’s position.Currents should be monitored withoutswitching the heading switch. Indis-criminately switching the heading switchwill result in currents with incorrect mag-nitude and polarity. Current magnitudescan be adjusted, if necessary, for 70 percenton intercardinal headings and for 100 per-cent on cardinal headings (adjust the FI-QIon north-south headings and the A-coil oneast-west headings).

e. The heading switch at a remote loca-tion can be used for manual operation byfirst setting the heading switch at theremote location to the ship’s magnetic head-ing and then setting the local-remote trans-fer switch for remote operation. Indis-criminately switching the local-remotetransfer switch will result in currents withthe incorrect magnitude and polarity.

475-4.5.4 OPERATOR CURRENTCONTROL EQUIPMENT. Coil cur-rents in the older, manual degaussing in-stallations (paragraph 475-4.1) should becontrolled as follows:

475-4.5.4.1 General Procedures.For each ship, the degaussing folder givesthe current needed for each coil for all posi-tions on the earth’s surface and for all head-ings. One or more of the coil currents mustbe changed when one of the following oc-curs:

a. When the ship passes from one Z-zone into another (see degaussing chart 1 indegaussing folder).

b. When the ship passes from one H-zone into another (see degaussing chart 2 indegaussing folder).

c. When the ship’s heading changesfrom one sector to another. The entirerange of headings from 0 to 360 degrees isdivided into a number of sectors, eachcovering a part of the whole range ofcourses. See the course correction setting,diagram 1 or 2; or course correction setting,table 1, 2 or 3, in the degaussing folder.None of the degaussing coil currents ischanged as long as the course remains inone sector; some of the coil currents must bechanged when the course changes from onesector to another.

S9086-QN-STM-010/CH-475

4-13

475-4.5.4.2 Detailed Adjustments.Changes required are as follows:

a. The FP-QP coil current is notchanged no matter how the heading of theship’s position changes.

b. The M-coil current must be changedwhen the ship moves from one Z-zone toanother. It is not changed when the shipmoves from one H-zone to another, or whenthe heading changes from one sector toanother.

c. The F, Q, FI-QI, L-, and A-coil cur-rents are not changed when the ship movesfrom one Z-zone to another, but must bechanged if the ship moves to a different H-zone, or the heading changes to a differentsector. In a few ships, exceptional condi-tions may require a departure from theforegoing schedule of changes. In all cases,the degaussing folder will show the cur-rents to be used.

S9086-QN-STM-010/CH-475

4-14

S9086-QN-STM-010/CH-475

5-1

SECTION 5. DEGAUSSING SYSTEM MAINTENANCE

475-5.1 PREVENTIVE MAINTE-NANCE

Preventive maintenance shall be performedin accordance with the appropriate PlannedMaintenance System (PMS) documentation.

475-5.2 CORRECTIVE MAINTE-NANCE

Degaussing system equipment requiringmaintenance can be grouped in two generalclasses: degaussing coils (cable, cable fit-tings, connection boxes), and control andpower equipment (control units,switchboards, power supplies, mag-netometers, generators). Maintenance in-formation for each class is available fromvarious sources.

475-5.2.1 DEGAUSSING COILS.See the ship’s detail drawings on degauss-ing for information on installed coils, theirlocation, connections, marking, and soforth. NSTM Chapter 300, Electric PlantGeneral, has instructions on the mainte-nance of this class of equipment.

475-5.2.2 CONTROL AND POWEREQUIPMENT. Applicable technicalmanuals on control and power equipmentcover specific information for installedequipment. NSTM Chapter 300, ElectricPlant General, outlines the general in-structions on the maintenance of most ofthis equipment (motors, generators,switchboards, circuit breakers, contactors,

relays). See NAVSEA 0967-LP-000-0160,Electronics Installation and Mainte-nance Book, for general instructions onthe maintenance of solid state equipment.

475-5.3 TECHNICAL INFOR-MATION SOURCES,DEGAUSSING EQUIPMENTAND SYSTEMS

Further information on degaussing equip-ment is available from:

a. Technical manuals for the operationand maintenance of degaussing power andcontrol equipment

b. Ship’s detail drawings for degaussingcoil installation

c. Ship’s degaussing folder on coil in-stallations, types of control and powerequipment installed, and coil turns and cur-rent settings.

d. NAVSEA S9475-AF-OMI-011,Degaussing Manual, covers detailed in-formation on design, installation, and main-tenance requirements of shipboard degauss-ing systems and equipment.

Personnel responsible for the operation,care and maintenance of degaussing sys-tems should be thoroughly acquainted withthese documents and should refer to themduring equipment maintenance.

S9086-QN-STM-010/CH-475

5-2

S9086-QN-STM-010/CH-475

6-1

SECTION 6. MAGNETIC RANGES AND RANGING

475-6.1 RANGE DESCRIPTION

A magnetic range is a station equipped tomeasure and record the magnetic field ofships that pass over measuring equipmentlocated at or near the bottom of the channelin which the ships travel. A ship is said tobe ranged when its magnetic field ismeasured at a magnetic range.

475-6.2 PURPOSE OF RANGING-CHECK RANGING

Check ranging determines that the ship’sdegaussing installation is operating satis-factorily. The following operating condi-tions are checked:

a. Adequacy of current settings indegaussing coils.

b. Performance of degaussing equip-ment and personnel.

475-6.3 PURPOSE OF RANGING -CALIBRATION

Calibration ranging serves the followingfunctions:

a. Determines initial degaussing coilcurrent settings.

b. Provides information for degaussingcharts.

c. Indicates when changes or modifica-tions are required to the degaussing instal-lation. Maintenance and updating ofdegaussing forms is presented in NAVSEAS9475-AC-PR-010, Degaussing Forms,Records, and Reporting Procedures.

475-6.4 FREQUENCY OF RANGING

All ships that have degaussing coils or aremagnetically treated by Flash-D (paragraph475-7.1.2) are required by CNO to perform

a satisfactory check ranging in accordancewith OPNAVINST C8950.2, MagneticSilencing. Any ship that exceeds the satis-factory check range limits must undergocalibration ranging or magnetic treatmentas soon as possible.

475-6.5 SHIP’S RESPONSIBILITIESFOR ACCURATE RANGING

All ships must proceed as follows:

a. The ship must pass directly over therange at a constant speed and heading.

b. The degaussing coils must be set cor-rectly.

c. The Range Officer must be notified ofthe coil settings.

d. The Range Officer must be notified ofthe ship’s draft, forward and aft, to thenearest 6 inches, for depth correction.

e. The Range Officer must be notified ofthe ship’s magnetic heading at the time theship crosses the degaussing range.

f. Ships with magnetometer-controlleddegaussing equipment, (e.g., type MCD),should report their millioersted readings aswell as the coil currents at time of crossingrange.

475-6.6 MINESWEEPER OFF-LOADPROCEDURES

Minesweepers shall off-load all un-authorized magnetic material and ensurethat all authorized magnetic material isstowed in its proper location before ranging.The Magnetic Material Control Officer isresponsible (check applicable minewarfareinstructions).

S9086-QN-STM-010/CH-475

6-2

475-6.7 SHIP’S DEGAUSSINGFOLDER

475-6.7.1 DEGAUSSING FOLDERCONTENT. The degaussing folder isan official ship log. It contains informationon the magnetic treatment of the ship, in-structions for the operation of the shipboarddegaussing system, degaussing charts,values for the coil current and loop turn set-tings, installation information forms, com-pass compensating forms, and a log sectionshowing all pertinent details of magnetictreatment and action taken on the ship’sdegaussing system.

475-6.7.2 DEGAUSSING FOLDERPREPARATION BY DEGAUSSINGRANGE PERSONNEL. The folder isprepared and issued to a ship by the Mag-netic Silencing Facility that renders the in-itial magnetic treatment and degaussingsystem calibration. During calibrationranging, induced field and perm field cur-rent magnitudes and polarities are es-tablished for each coil, and loop turns areestablished for all loops. Current settingcharts are prepared to provide the ship’spersonnel with up-to-date magnitudes andpolarities to be used for any position on theearth’s surface and any heading of the ship.

S9086-QN-STM-010/CH-475

7-1

SECTION 7. MAGNETIC TREATMENT

475-7.1 TYPES

The two types of magnetic treatment com-monly used are deperming and flash-D.Deperming is used only for ships that aredegaussed by coils. Flash-D is used forships that are degaussed by magnetic treat-ment alone and are not equipped withdegaussing coils.

475-7.1.1 DEPERMING. Depermingis a large-scale way of demagnetizing awatch. Its purpose is to reduce permanentlongitudinal and athwarthship magnetiza-tion and stabilize permanent vertical mag-netization. When the permanent mag-netism becomes excessive, to the pointwhere the degaussing coils cannot provideadequate compensation, the permanentmagnetism must be reduced. The process ofremoving permanent magnetism is called"deperming." Ships are usually depermedwhen then are first commissioned, and thenagain later, as determined necessary by adegaussing range.

475-7.1.2 FLASH-D. Flash-D is amagnetizing process that eliminates per-manent longitudinal and athwartship mag-netization. It produces a permanent ver-tical magnetic field that is equal to and op-posite the induced vertical magnetic fieldfor a specific geographic operating area.

475-7.2 EFFECTIVENESS

Induced vertical magnetization changeswith a ship’s location on the earth; per-manent vertical magnetization does not.Therefore, the cancellation of the verticalmagnetization by flash-D is complete onlyfor a particular value of the earth’s mag-netic field. When the ship moves to a placewhere the earth’s magnetic field is dif-ferent, the cancellation is not as good and

the ship is not as well degaussed. Since in-duced athwartship and longitudinal mag-netization change with the heading, mag-netic treatment is not used to reduce thesefields. For this reason, degaussing by mag-netic treatment alone is not extensivelyused on ships having other than limitedoperating areas.

475-7.3 FREQUENCY

All new ships required to be degaussedmust be depermed or have a flash-D mag-netic treatment. Ships exceeding the mag-netic field limits (with onboard degaussingsystems optimally adjusted) of NAVSEAS5475-AC-MMM-010/(C), Magnetic Rang-ing and Calibration of Degaussing Sys-tems - Degaussing PerformanceCriteria, must undergo calibration rang-ing, be depermed, or have a flash-D mag-netic treatment.

475-7.4 SHIP’S RESPONSIBILITY

The nearest magnetic treatment facilityshould be contacted and the ship scheduledfor magnetic treatment when the ship hasbeen notified that magnetic treatment is re-quired. The ship will be issued instructionsby the magnetic treatment facility as to theship requirements and responsibilitieswhile using the magnetic treatment facility.

475-7.4.1 SPECIAL PRECAUTIONSDURING MAGNETICTREATMENT. During deperming ofsurface ships and submarines, as well asduring flash-D treatment, high magneticfield intensity on the order of1,600 amp/meter can be measured in andnear the ship. Some local fields may begreater and various individual componentsas well as operating equipment may be al-tered by this magnetic field strength.

S9086-QN-STM-010/CH-475

7-2

Equipment that may be affected isdescribed in the following paragraphs alongwith special precaution procedures to be ob-served to avoid difficulties.

475-7.4.2 EQUIPMENT ANDORDNANCE PRECAUTIONS.Special precautions concerning guided mis-siles, missile guidance and control sections,rocket motors and missile boosters, electricbomb fuses, nuclear weapons, and ship’sequipment must be adhered to before andafter arrival at the magnetic treatmentfacility.

475-7.4.3 SUBMARINE GENERICEQUIPMENT PRECAUTIONS.Equipment aboard submarines has com-ponents that may be influenced by the mag-netic treatment field. Although this equip-ment may not be addressed specifically, thefollowing considerations give guidance onwhether to pursue offloading procedures.

475-7.4.3.1 Effects on Computers.Computer elements such as logic com-ponents (transistor transistor logic [TTL],complementary metal oxide semiconductors[CMOS], emitter coupled logic [ECL], resis-tor transistor logic [RTL], medium-scale in-tegration [MSI], and large-scale integration[LSI] circuits, read-only memories [ROMS],programmable read-only memories[PROMS], erasable programmable read-only memories [EPROMS], electronicallyerasable programmable read-only memories[EEPROMS], and random access memories[RAM]) are not affected by the demagnetiz-ing magnetic treatment field. A variety ofcomputer magnetic storage items, however,should be protected by offloading or storagein shielded lockers before magnetic treat-ment. These items are:

a. Computer floppy disks.

b. Personal and mainframe computerhard drives.

c. All magnetic memory elements forweapons systems.

NOTE

Although mainframe com-puter tape backups can beremoved easily, mainframeand personal computerhard drives require con-siderable effort to removeand can be protected bestby removing the computerwith the hard drive in-stalled. (To do so, positionthe hard drives of personalcomputers to the move-protected position.)

475-7.4.3.2 Effects of Other Mag-netic Elements. All magnetic ele-ments dependent upon magnetization foroperation may be affected by the magnetictreatment field. Examples of items thatcould be affected are:

a. Video- and audiotapes

b. Credit cards such as are used forbank deposit or withdrawal.

475-7.4.3.3 Effects on Cathode RayTube (CRT) Displays. Displays (nowin use for radar presentations) aboard shipare devices that function by electrostatic orelectromagnetic deflection. Those thatfunction by electrostatic deflection (such asthe type 25G raster scanned deflection sys-tem) would not be influenced by electromag-netic deperming or degaussing. It is pos-sible that magnetic fields caused bydeperming may influence the electromag-netic deflection display types. Afterdeperming is complete and magnetic fieldlevels aboard ship are normal, the magnetichistory of some display devices, includingtelevision sets, can be reset by turning the

S9086-QN-STM-010/CH-475

7-3

display on and off and then on again. Otherelectromagnetic displays, such as the type25A and 25D types, have been designed tothe requirements of MIL-STD-2036,General Requirements for ElectronicEquipment Specifications, and are im-mune to electromagnetic interference due tointernal magnetic shielding. Any residualinterference with a display due to deperm-ing should be reported to the respectiveequipment program manager for resolutionafter the on-off-on procedure has been im-plemented.

475-7.4.4 SPECIFIC SUBMARINEWEAPONS PROTECTIONPROCEDURES.

475-7.4.4.1 Strategic WeaponsProtection. Precautions for protectionof submarine strategic weapons aredescribed in SSPINST 8950.2, Subj:"Procedures for Protection of FleetBallistic Missile (FBM) StrategicWeapon System Components DuringFlash Deperm Treatment of an SSBN598, 608, 616, (616-659 including the C-4Backfit configurations), and 726 Class(TRIDENT) Submarines."

475-7.4.4.2 MK48 ADCAP TorpedoProcedures During Deperming/Flash Magnetic Treatment.Current protection procedures for the MK48ADCAP Torpedo are as follows:

a. No torpedoes in firing tubes duringmagnetic treatment.

b. Torpedo room secured with allhatches closed.

c. Deperm cables shall not pass within0.66 meter of torpedoes in storage racks.

475-7.4.4.3 TOMAHAWK MissileOffload and Protection ProceduresDuring Deperming/Flash MagneticTreatment. Current protection proce-dures for the Tomahawk missile aboardsubmarines requires that the missiles be of-floaded during the magnetic treatmentprocess.

475-7.4.5 SPECIFIC SUBMARINEEQUIPMENT PROTECTION PRO-CEDURES DURING DEPERMING/FLASH MAGNETIC TREATMENT.Precautions for the protection of the ship’s

installed equipment are as follows:

a. Radio Navigation and Com-munication Equipment: AN/BLD-1,AN/WLQ-4, AN/WLR-8, AN/WRN-5,AN/SRN-19 and OMEGA Set AN/BRN-7.The magnetic tapes used to load the com-puter portion of the AN/WRN-5 and theAN/BRN-7, and the cassette tapes used forrecording with the AN/SRN-19, shall beremoved and stored off the ship in a clean,dry area away from deperming fields. Themagnetic tape cartridge assembly should bestored in a clean plastic bag after it isremoved from the unit. The magnetic tapeitself should not be touched or scraped. Thetwo AN/WRN-5 magnetic core memorymodules, MFR-12813 and MPN625521-801, and the AN/BRN-7 corememory unit, MU-6O1URN, shall beremoved from the ship and stored in aclean, dry area away from all depermingfields during flash-deperm. TheAN/SRN-19 radio receiver should be turnedoff during flash-deperm. The AN/BLD-1,AN/WLQ-4, AN/WLR-8 and WLR-8 Aug-mentation systems should be de-energizedin accordance with the applicable technicalmanuals. All magnetic tapes shall bestored in appropriate magnetic tape casesand removed from the ship.

AN/WRR-7 VERDIN - Remove the RD-350Magnetic Tape Unit (MTU) from the proces-sor (CP-1071) and the spare RD-350 and

S9086-QN-STM-010/CH-475

7-4

remove them from the ship to a clean, dryarea away from the deperming fields.

b. Infrared Viewers and InfraredMetascopes. Infrared viewers or infraredmetascopes, if aboard, shall be removedduring flash-deperm, as a precautionarymeasure.

c. Fire Control Equipment, includ-ing MK 113 MOD 9, MK 117, MK 118,CCS MK1 (all mods), CCS MK2 (allmods), and AN/BSY-1. All fire controlequipment, including MK 113 MOD 9, MK117, MK 118, CCS MK1 (all mods), CCSMK2 (all mods), and AN/BSY-1 shall be de-energized in accordance with the applicabletechnical manuals.

d. Magnetic Tape System UNIVAC1840 (RD-358) and 0J-172 (DEAC).Remove the magnetic tapes from the tapetransports, insert them in shipping con-tainers, and place them in the assignedstorage cabinet.

e. Ships Inertial Navigation System(SINS) MK 2 MOD 1 Equipment. Thefollowing special precautions are requiredfor the SINS components of the naviga-tional subsystem installed on SSN 594 class(614-615).

1. The SINS shall be turned off inthe normal manner. If desired, the SINSmay be left in the PRIMARY POWERMODE STANDBY to keep heat on thegyros and thus reduce startup time slightly.

2. Remove the VERDAN computerdrawer from the navigation console andfrom the auxiliary control console. Removethe spare VERDAN magnetic memory, P/N55370-304. Store this equipment off theship in a clean, dry area away from thedeperming fields.

3. Inertial components may be leftinstalled during deperming operations.Spare inertial components may be left on-board if they are not stored within 2 metersof the hull structure. Spare inertial com-ponents may be moved temporarily within

the submarine to meet the distance limita-tion.

4. Once the SINS has been shutdown for deperming, adequate time for tem-perature stabilization should be allowedafter restarting and before any scheduledoperations involving the SINS. Sufficienttime should be allowed for normal startup,temperature stabilization and calibrationprocedures necessary to attain a stable,well-settled system.

5. Following deperming, scale factorsand gyro bias runs shall be conducted be-fore use of the system for navigation.

NOTE

Detailed procedures forremoval and replacement ofthe SINS computers and forthe SINS operation andcalibration are covered in:NAVSEA 0324-LP-047-7010through 7120, TechnicalManual for SINS MK 2 MOD1.

f. SINS MK 3 MOD 4 and MOD 6Equipment. The following special precau-tions are required for the SINS componentsof the navigation subsystem installed onSSN 637 class and SSN 671 submarines.

1. Preferably keep the SINS in theNAVIGATE mode with the monitor closedloop. Any other mode, including OFF,however, is acceptable.

2. Service the SINS, if ON, from thestatic inverter (primary) or a ship servicegenerator (secondary).

3. All the operating SINS com-ponents shall be left installed during thedeperming operations. The following sparecomponents may be left on board if they arenot stored within 2 meters of the hull struc-ture. These components may be movedtemporarily within the submarine to meetthis distance limitation:

S9086-QN-STM-010/CH-475

7-5

(a) Spare gyros (2), P/N 1686038-2or -4.

(b) Spare PIPAs (2), P/N1685291-2.

(c) Spare magnetic drum memory(1), P/N 1601871 on MOD 4, P/N 633083 onMOD 6.

(d) Spare magnetic core memory(1), P/N 1602144 on MOD 4, P/N 753141 onMOD 6.

(e) Module test set on MOD 6only.

(f) Spare magnetic tape assembly(1), P/N 2686585-1 for module test set onMOD 6 only.

4. Following deperming, reset theSINS, using 8 hours of data, and then per-form the gyro scale factor calibration usingthe Theta "D" procedure.

NOTE

Detailed procedures foroperation and calibration ofthe SINS are covered in:NAVSEA 0324-LP-064-5000series, Technical Manualfor SINS MK 3 MOD 4 andNAVSEA 0924-LP-022-1000Technical Manual for SINSMK 3 MOD 6.

g. Dual Miniature Inertial Naviga-tion System (DMINS), AN/WSN-1(V)2.The following special precautions are re-quired for the DMINS components of thenavigation system installed on SSN 594class, SSN 637 class, and SSN 688 classsubmarines.

1. Turn off the DMINS in the normalmanner.

2. Leave all components of theDMINS, including the spare IMU, installedduring the deperming operations.

3. Following deperming, perform VMand gyro calibration.

NOTE

Once the DMINS has beenshut down for deperming,adequate time should be al-lowed after restarting fornormal startup and calibra-tion procedures to attain astable, well-settled system.Detailed procedures for theDMINS shutdown, turn-on,and calibration for theseships are included in theapplicable navigationoperating procedures andin the SSN 688 Class ShipSystems Manual, volume 6,part 3, chapter 1, section 4.

h. Recorder/Reproducer. Specialprecautions are required for the AN/UYH-2and AN/BYH-1 SUBRASS installed on SSN637 class and SSN 688 class submarinesequipped with MK 117, MK 118, CCS MK1,(all mods), CCS MK2 (all mods), andAN/BSY-1.

AN/BSY-1, and Combat Control SystemMagnetic Storage Media. Blank/spare disksand tapes, as well as those with informationrecorded on them, need protection from thedeperm fields. The following magneticdata/program storage media shall beremoved before beginning the flash depermprocedure:

1. SUBRASS (Submarine RandomAccess Storage Set) DTD’s (Data transferdevices): CC-3, Acoustic-3, OTH (Over theHorizon), TLAM (Tomahawk Land AttackMissile) mission.

2. AN/ASH-34 tape cartridges.

3. Work tape recorder (Studer-Revox) cassettes.

4. Tactical Support Device (TDS)hard and floppy disks.

S9086-QN-STM-010/CH-475

7-6

The magnetic disk packs used in therecorder/reproducer shall be stored in thecarrying case or in the equipment.

NOTE

Some SSN 688 class sub-marines may have providedfor the storage of the diskpacks in a stowage lockerdesigned to protect themagainst strong magnetic fields.

i. AN/BQQ-5 Sonar. Special precau-tions are required for the AN/BQQ-5 sonarinstalled on SSN 637 class and SSN 688(pre-SSN 751) class submarines. Removeall backup program tapes and store themoff the ship in a clean, dry area away fromthe deperming fields.

j. SSBN 726 (TRIDENT) Class Sub-marines CCS Subsystems (MK 118 FCS)and AN/BQQ-6 Sonar System.

1. In accordance with existingoperating procedures, turn off the electricalpower to all equipment except the cesiumbeam frequency standard.

2. Securely fasten the equipmentdrawers and doors in the closed position.

3. Remove the magnetic tapes anddisc packs, including the spares not housedin a protective environment, and store themoff the ship in a clean, dry area away fromthe deperming fields.

4. Upon completion of the deperm-ing, return the tapes and discs to their loca-tions and power up the equipment in ac-cordance with the existing operating proce-dures.

k. AN/WSN-2 and AN/WSN-2A,Stabilized Gyrocompasses. The follow-ing special precautions are required for theAN/WSN-2 installed on SSN 688 class sub-marines (716-725 and 750) and theAN/WSN-2A installed on SSN 688 classsubmarines (751-773).

1. Turn off AN/WSN-2 or 2A in nor-mal.

2. The spare inertial measuring unit(IMU) should be installed in the storagecontainer, and the navigation control group(NCG) door should remain closed duringdeperming operations.

l. AN/WSN-3, ElectricallySuspended Gyro Navigator (ESGN).The following general precautions are re-quired for the AN/WSN-3 installed on SSN688 and SSN 637 class submarines:

1. The ESGNs may be in any mode(cage, stabilized, or off). The spare IMUshould be installed in the storage container,and the NCG doors should remain closedduring the operation. Any spare modulesnormally stored within 1.2 meters of theouter hull should be removed to a morecentral location within the ship.

m. Other Equipment.

1. Remove the magnetic tapes fromthe tape transports. Place all the magnetictapes in magnetic tape stowage lockers.

2. Remove the following equipmentfrom the ship before magnetic treatment:

(a) Chronometers and navigationwatches.

(b) Magnesyn compass transmit-ters and soft iron compass correctors(flinders bars).

NOTE

If specific equipment is notlisted and it is suspectedthat magnetic treatment ordegaussing could affect it,contact the respectiveequipment program mana-ger.

(c) Cesium Beam Clocks for IMAstorage.

S9086-QN-STM-010/CH-475

7-7

NOTE

The equipment must beplugged into a powersource immediately. It hasa battery supply capable ofmaintaining the equipmentfor 1/2 to 2 hours. If keptwithout external power forlonger periods, the clocksmust be sent back to alaboratory for recalibra-tion.

475-7.4.6 SURFACE SHIPGENERIC EQUIPMENTPRECAUTIONS. Equipment aboardsurface ships possesses components thatmay be influenced by the magnetic treat-ment field. Although this equipment maynot be addressed specifically, the followingconsiderations give guidance on whether topursue offloading procedures.

475-7.4.6.1 Effects on Computers.Computer elements such as logic com-ponents (TTL, CMOS, ECL, RTL, MSI andLSI circuits, ROMS, PROMS, EPROMS,EEPROMS, and RAMS) are not affected bythe demagnetizing magnetic treatmentfield. However, a variety of computer mag-netic storage items should be protected byoffloading or storage in shielded lockers be-fore magnetic treatment. These items are:

a. Computer floppy disks

b. Personal and mainframe computerhard drives

c. All magnetic memory elements forweapons systems.

NOTE

Although mainframe com-puter tape backups can beremoved easily, mainframeand personal computerhard drives require con-siderable effort to removeand can be best protectedby removing the computerwith the hard drive in-stalled. (To do so, positionthe hard drives of personalcomputers to the move-protected position.)

475-7.4.6.2 Effects on Other Mag-netic Elements. All magnetic ele-ments dependent upon magnetization foroperation may be affected by the magnetictreatment field. Examples of items thatcould be affected are:

a. Video- and audiotapes

b. Credit cards such as are used forbank deposit or withdrawal.

475-7.4.6.3 Effects on Cathode RayTube (CRT) Displays. Displays (nowin use for radar presentations) aboard shipare devices that function by electrostatic orelectromagnetic deflection. Those thatfunction by electrostatic deflection (such asthe type 25G raster scanned deflection sys-tem) would not be influenced by electromag-netic deperming or degaussing. It is pos-sible that magnetic fields caused bydeperming may influence the electromag-netic deflection display types. Afterdeperming is complete and magnetic fieldlevels aboard a ship are normal, the mag-netic history of some display devices, in-cluding television sets, may be reset byturning the display on and off and then onagain. Other electromagnetic displays,such as the type 25A and 25D types, have

S9086-QN-STM-010/CH-475

7-8

been designed to the requirements of MIL-STD-2036, General Requirements forElectronic Equipment Specifications,and are immune to electromagnetic inter-ference due to internal magnetic shielding.This is more likely to happen to a color dis-play, where the color presentations are ex-tremely sensitive to an interfering magneticfield. Such interference may be remediedby providing separation between thedegaussing coil and the display. (Thiswould be more likely to happen to displaysmounted below deck, in close proximity tothe degaussing coils. Where no degaussingcoils exist, there is no potential for this in-fluence.) Any potential interference with adisplay by a degaussing coil or any residualinterference with a display due to deperm-ing should be reported to the respectiveequipment program manager for resolutionafter the above on-off-on procedure hasbeen implemented.

475-7.4.7 SPECIFIC SURFACESHIP WEAPONS PROTECTIONPROCEDURES DURING DEPERM-ING MAGNETIC TREATMENT.Precautions for the protection of the guidedmissiles, missile sections, and the ship’s in-stalled equipment are as follows:

a. Guided Missiles, Missile Sec-tions, and Torpedoes. During ship mag-netic treatment missiles must be storedonly in the shipboard locations listed below.The precautions outlined for each locationmust be observed. No missile checkout op-erations should be conducted during themagnetic treatment.

1. Missiles inside a closed steelhull or a closed regular steel stowagemagazine. The doors and hatches of thestowage compartment or magazine must beclosed.

2. Missiles inside a closedaluminum stowage magazine. Thedoors and hatches must be closed. Depermcables must be supported away from the

side or overhead of magazine so as not topass within 0.66 meter of a missile.

3. For ASROC missiles whollywithin a launcher. Missiles must notproject from the launcher, and depermcables must not pass over the launcher.

4. Missiles other than ASROC.Such missiles must not be stowed on ex-posed launchers or inside box launchersoutside the hull during the ship magnetictreatment.

5. NATO SEASPARROW MissileSystem (NSSMS) - In addition to the mis-sile procedures covered in (a), the followingprocedures are to be observed for theSEASPARROW Missile.

(a) All spare programmable readonly memory (PROM) circuit cards shouldalso be stored in appropriate magneticstowage containers/lockers and those in-stalled in equipment be left installed withall cabinet doors closed throughout thedeperming procedure.

(b) As a further precaution, alldoors and hatches to all NSSMS equipmentshould be closed and secured during thedeperming procedure.

6. All Missile Systems - Removemagnetic tapes from tape transports. Placeall magnetic tapes in magnetic tape storagelockers.

7. Torpedoes shall not be stored inMK 32 torpedo tubes during magnetictreatment.

8. Torpedoes stored in magazineshall be treated as missiles. Paragraphs 1and 2 preceding apply.

b. Close-in Weapons System (CIWS)MK 15 ALL MODS.

1. Before magnetic treatment.

(a) Store all MK 15 CIWS Opera-tional Program tapes, diskettes, and tapecartridges inside the CIWS Local Controlroom or remove from the ship.

S9086-QN-STM-010/CH-475

7-9

(b) Remove the motion transducerand its bracket (P/N 5191128) as a unitfrom the M61A1 20MM gun per OP 4154Series (Block 0) and SW221 Series (Block1). Store motion transducer and its bracketin the CIWS local control room or removefrom ship.

2. Following magnetic treat-ment:

(a) Replace the motion transducerand bracket.

(b) Reload CIWS Operational Pro-gram.

475-7.4.8 SPECIFIC SURFACESHIP INSTALLED EQUIPMENTPROTECTION PROCEDURESDURING DEPERMING MAGNETICTREATMENT. Precautions for theprotection of ship installed equipment areas follows: Field and laboratory tests, todate, have indicated that magnetic treat-ment produces no adverse effects on manymagnetically sensitive devices found aboardship except for compasses andchronometers and that, excepting these, nospecial precaution need to be taken. Thesetests have been made on aircraft instru-ments, fuses, depth charges with magneticpistols, and torpedoes with magnetic ex-ploders. Special precautions may, however,be required with the advent of new devices.

a. Protection of magnetic tapes.

1. Remove the magnetic tapes fromthe tape transports. Place all the magnetictapes in magnetic tape stowage lockers.

b. Chronometers, navigationwatches, and magnetic compasses.Remove the following equipment from theship before magnetic treatment:

1. Chronometers and navigationwatches - Chronometers are to be removedfrom the ship before magnetic treatmentwhile the degaussing coils are secured and

placed where the field due to the treatmentwill not exceed 100 microtesla. (The mag-netic field of the earth is approximately50 microtesla.) Replacement on the shipmust be done while the degaussing coils aresecured. It is generally unnecessary toremove ordinary clocks and watches duringmagnetic treatment, although this may bedone if desired.

2. Remove magnetic compasses andsoft iron compass correctors under the fol-lowing conditions:

Deperming cables should not be riggedcloser than 4.5 meters to any magnetic com-pass on the ship, including the steering,standard, Magnesyn master, and life boatcompasses. If this precaution cannot be ob-served, the compass systems, remote in-dicating devices, permanent magnet correc-tors, and transmitters should be removed.

Soft iron correctors must be removed fromthe ship during all magnetic treatments.The quadrantal spheres may also beremoved if local experience has shown it tobe desirable, although it is not usually con-sidered necessary. Compensating magnetsneed not be removed. All magnetic com-passes, including standard, steering, andlifeboat compasses, must be put in the freeoperating position unless they are removedfrom the ship. Magnetic treatment cablesshould not be rigged nearer than 2.0 metersto a vacated compass position.

c. Protection of the Ship’s Inertialand Compass Navigation Systems.

1. Clearance or removal of thecompass - Deperming cables should not berigged closer than 4.5 meters to any mag-netic compass on the ship, including steer-ing, standard, and Magnesyn master com-passes. If this precaution cannot be ob-served, the compass systems, remote in-dicating devices, permanent magnet correc-tors and transmitters should be removed.The compass clearance distance for sub-marines may be taken as 3 meters insteadof 4.5 meters.

S9086-QN-STM-010/CH-475

7-10

Soft iron correctors must be removed fromthe ship during all magnetic treatments.The quadrantal spheres may also beremoved if local experience has shown it tobe desirable, although it is not usually con-sidered necessary. Compensating magnetsneed not be removed. All magnetic com-passes, including standard and steeringcompasses, must be put in the free operat-ing position unless they are removed fromthe ship. Magnetic treatment cables shouldnot be rigged nearer than 2.0 meters to avacated compass position.

After a ship has been given a magnetictreatment, it should be swung for adjust-ment of the magnetic compasses before sail-ing. When practicable, this should not takeplace the same day as the treatment. If ab-solutely necessary, the magnetic compassesmay be adjusted on the same day, but in nocircumstances should a ship be swung until5 hours have elapsed since the treatment.

2. The ship’s inertial navigationsystem (SINS).

Precautions for protection of the ship’s in-ertial navigation system (SINS) MK 3,MOD 4, MOD 5, MOD 6, MOD 7, andMOD 8 during flash-deperm of surfaceships are as follows:

(a) Preferably keep the SINS inthe NAVIGATE mode with the monitor inclosed loop. Any other mode, includingOFF, however, is acceptable.

(b) Service the SINS, if ON, fromthe static inverter (primary) or a ship ser-vice generator (secondary).

(c) All operating SINS componentsshall be left installed during the depermingoperations. The following spare com-ponents may be left on board if they are notstored within 2 meters of the hull structure.These components may be moved tem-porarily within the ship to meet this dis-tance limitation:

• Spare gyros

• Spare PIPAs

• Spare magnetic drum memory onMOD 4, MOD 5, MOD 6, andMOD 8

• Spare magnetic core memory onMOD 4, MOD 5, MOD 6, andMOD 8

• CP-642B computer spare corememory chassis and controlmemory chassis on MOD 7

• Module test set on MOD 6 andMOD 7

• Spare magnetic tape cartridge formodule test set on MOD 6 andMOD 7.

(d) Detailed procedures forremoval and replacement of the SINS com-ponents and the operation of the SINS arecovered in the applicable technical manualslisted below:

• NAVSEA 0324-LP-064-5110through 5620, TechnicalManual for SINS MK 3 MOD 4




• NAVSEA 0924-LP-045-5010through 5160, TechnicalManual for SINS MK 3 MOD 8.

(e) Following deperming, reset theSINS using 8 hours of data; then performthe gyro scale factor calibration using theTheta D procedure.

S9086-QN-STM-010/CH-475

7-11

d. Other Surface Ship Equipment.

1. Remove magnetic tapes from thetape transports. Place all magnetic tapes inmagnetic tape stowage lockers.

2. Remove the following equipmentfrom the ship before magnetic treatment:

(a) Chronometers and navigationwatches

(b) Magnesyn compass transmit-ters and soft iron compass correctors(flinders bars).

NOTE

If specific equipment is notlisted and it is suspectedthat magnetic treatment ordegaussing could affect it,contact the respectiveequipment program mana-ger.

475-7.4.9 CLEARANCE OF AM-MUNITION, PYROTECHNICS, EX-PLOSIVES, AND INFLAMMABLEMATERIALS. All munitions, ex-plosives, or flammable material formingpart of the ship’s regular equipment, exceptdepth charges and torpedoes, shall beproperly stowed below decks in magazinesor topside in ready-service lockers. Cablesshall clear ready-service lockers, depthcharges, and torpedoes by at least0.6 meter, and wooden boxes containingpyrotechnics or other flammables by atleast 1.2 meters. All tanks, fuel oilbunkers, cofferdams, dry cargo spaces, andullage plates are to be closed. Depermingcables are to be kept at least 1.2 metersaway from the vents of such spaces.

475-7.4.10 CLEARANCE OF FUELOIL BUNKERS. In the case of shipsother than tankers, it is desirable thatturns be placed so that they do not lie over

a fuel oil bunker and are at least 1 meterfrom any bunker bulkhead when its loca-tion is known.

475-7.4.11 RESTRICTIONS ON THEMAGNETIC TREATMENT OFTANKERS. Tankers ordinarily used tocarry combustible liquids of any kind mustnot be magnetically treated unless theymeet one of the following conditions:

a. The ship shall be cleaned out andcertified to be "gas free for personnel andfire."

b. The ship shall be cleaned out andcertified to be "gas free for personnel only"not more than 24 hours before the magnetictreatment.

c. All cargo tanks, adjacent compart-ments, and other spaces suspected of con-taining explosive gases shall be cleaned outand proven free of explosive gases by themethod prescribed in NSTM Chapter 074,Welding and Allied Processes andNSTM Chapter 541, Petroleum FuelStowage, Use and Testing, not more than24 hours before treatment.

475-7.4.12 RESTRICTION ONDEPERMING OF SHIPS (OTHERTHAN TANKERS) THAT CARRYCOMBUSTIBLE LIQUIDS WITH AFLASH POINT BELOW 66DEGREES C. Ships, other thantankers, that carry gasoline, kerosene orany other liquid with a flash point below66 degrees C in built-in structures justbelow the weather deck, just within the hullplating or in separate containers stowedjust below the weather deck or near the hullplating, may be depermed under any one ofthe conditions below:

a. After discharge of the combustibleliquid, provided that the precautions, ex-actly as specified for tankers in the preced-ing paragraphs, are observed.

S9086-QN-STM-010/CH-475

7-12

b. Tanks or containers are at least95 percent full. Compartments adjacent tothese tanks or storage spaces containingthe combustible liquid in separate con-tainers shall be cleaned and proven gas freeby the method prescribed in NSTM Chapter074, Welding and Allied Processes andNSTM Chapter 541, Petroleum FuelStowage, Use and Testing, or certified"gas free for personnel" not more than24 hours before the magnetic treatment.

475-7.4.13 RESTRICTIONS ONMAGNETIC TREATMENT OFSHIPS CARRYING EXPLOSIVESAS CARGO. Ships whose cargo con-tains explosives or incendiary material maybe magnetically treated only if:

a. The explosives are properly stowedbelow decks in accordance with applicableregulations for such stowage, and no suchmaterial is loaded just below the weatherdeck or near the hull plating.

b. Regulations governing the docking ofsuch ships are complied with.

c. The precautions to prevent fire givenin paragraphs 475-1.2.2 through 475-1.2.2.8are rigidly observed.

Ships carrying a waiver permitting loadingof the ammunition in a manner not in ac-cordance with normal regulations or shipsnot conforming to the restrictions aboveshall not be magnetically treated. Thisparagraph does not apply in the case of am-munition and explosive weapons carried bythe ship for its own use.

475-7.5 DEGAUSSING FOLDERFOR DEPERMED SHIPS

A ship’s degaussing folder is also preparedfor ships that are degaussed by magnetictreatment. These folders are prepared bythe Magnetic Silencing Facility thatrenders the initial magnetic treatment. Alog section shows details of the magnetictreatment and action taken on the ship aswell as directions on preparing the degauss-ing charts that show the areas of operationin which the ship is satisfactorilydegaussed. If the degaussing folder is lost,a replacement can be obtained by applica-tion to the nearest Magnetic SilencingFacility.

S9086-QN-STM-010/CH-475

8-1

SECTION 8. COMPASS COMPENSATING INSTALLATION

475-8.1 PURPOSE/DESCRIPTION

Degaussing coils must produce large mag-netic fields in order to provide satisfactorydegaussing. Unless neutralized in thevicinity of the magnetic compass, thesefields may be of sufficient magnitude tomake the compass useless for navigation.Compass compensating coils are used to setup a compensating magnetic field that isequal and opposite to the degaussing coilfield in the immediate vicinity of the com-pass.

475-8.1.1 VERTICALCOMPONENT. Almost all degauss-ing coils create a vertical component of amagnetic field at the compass. A verticalcomponent at the compass causes the com-pass to deviate when the ship heels, eventhough it will usually cause no deviationwhen the ship is on an even keel. A com-pass compensating coil, called the heelingcoil, is used to compensate for the verticalcomponent of a magnetic field caused by thedegaussing coils. The heeling coil is placedin a horizontal plane around the binnacle,usually at the level of the compass needle,with its vertical axis passing through thecenter of the compass. A heeling coil,hereafter referred as the compensation ele-ment for the "H" component, is used in alltypes of compass compensating coil as-semblies. The heeling (H) coil compensatesby canceling the total effect of verticaldegaussing, which when the ship heels, con-tains a horizontal magnetic field componentthat would deflect the compass.

475-8.1.2 HORIZONTALCOMPONENT. The horizontal com-ponent of a magnetic field at the compasscauses compass deviations whether or notthe ship is on an even keel. Deviation dueto degaussing on any heading can be ob-tained by subtracting the magnetic compass

reading with degaussing OFF from themagnetic compass reading with degaussingON. The horizontal component of a mag-netic field is compensated by two perpen-dicular vertical coils or pairs of coils.

475-8.1.2.1 Horizontal ComponentError. In figure 475-8-1, E representsthe horizontal component of the magneticfield of earth, D the horizontal componentof the magnetic field produced by adegaussing coil and R the resultant field.The magnetic compass will point in thedirection of R and will therefore be in errorby the angle θ. When the ship changesheading, D will move with it and θ, the com-pass error or deviation caused by degauss-ing, will change with the heading. This er-ror can be eliminated by installing compasscompensating coils to produce a magneticfield equal to -D at the compass. The resultis to cancel the component D produced bythe degaussing coil so that the compass willpoint in the direction of the magnetic fieldof earth.

475-8.1.2.2 Horizontal ComponentError Compensation. A horizontalcomponent of a magnetic field equal to -Dcan be produced by two intercardinallymounted coils that produce NE and NWcomponents of a magnetic field (figure475-8-2).

475-8.1.3 INTERCARDINAL COILCOMPENSATION. The NE and NWcoils are known as intercardinal coils be-cause they produce magnetic fields that arein the intercardinal directions when theship is headed north. A single NE coil canbe used as illustrated in figure 475-8-2, oralternatively, a pair of NE coils, one at eachend of a diameter passing through the axisof the compass. The same is true of NWcoils.

S9086-QN-STM-010/CH-475

8-2

Figure 475-8-1. Degaussing CoilMagnetic Field

Effect.

Figure 475-8-2. Compensation ofIntercardinal Compo-nents of Degaussing

Coil MagneticField.

475-8.1.4 COMPENSATION CUR-RENT RELATIONSHIP TO THEDEGAUSSING CURRENT. Themagnitude of the magnetic field produced atthe compass by a degaussing coil varieswith the degaussing coil current. The mag-netic field produced by the compass com-

pensating coils must also vary in the sameway to compensate for this field. This is ar-ranged by connecting the equipment so thatthe compass compensating coil current isalways the same fraction of the degaussingcoil current. When this fraction is adjustedso that the magnetic fields produced by thedegaussing coil and the compass compen-sating coil are equal and opposite, thebalance between them is maintained nomatter how the degaussing coil currentvaries. Doubling the degaussing coil cur-rent, for example, would double the mag-netic field produced at the compass by thedegaussing coil and would also double thefield produced by the compass compensat-ing coils used to compensate the degaussingcoil.

475-8.1.5 COMPENSATING COILCONSTRUCTION. Most of the stan-dard types of compass compensating coilsare furnished as a coil assembly that con-sists of enclosures to protect the coils fromdamage, a single heeling coil to compensatethe vertical component, and two coils, ortwo pairs of coils, to compensate the inter-cardinal components. Each coil consists ofa number of windings, one winding for eachdegaussing coil that produces a magneticfield at the compass.

475-8.1.6 TYPES OF COILS. Aconsiderable number of compass compen-sating coils have been developed. Some ofthem are now obsolete and have beenreplaced by standard types. Other types, ifin good condition, shall be left in placewhere now installed. New installationsshall use standard types only. Standardtypes of compass compensating coils utilizeintercardinally mounted coils. These instal-lations are more adaptable to a greatervariety of binnacle arrangements and areless dependent upon quadrantal sphere andflinder bar conditions.

S9086-QN-STM-010/CH-475

8-3

475-8.1.6.1 Acceptable Old-StyleCompass Compensation Coils.The following coils are to be left in place ininstallations where they now exist providedthe coils are in good condition and there isno indication of approaching failure, butthey are not to be used for new installationsor replacements:

a. Type K

b. Type K-1

c. Type Filled K

d. Type R-1.

475-8.1.6.2 Standard Present Typesof Compass Compensation Coils.Present standard types of compass compen-sating coils and their uses are described intable 475-8-1. These are the coils to be usedfor new installations and replacements.The type K-2 coil is illustrated in figure475-8-3.

475-8.1.7 COIL POWER SUPPLY.The power source used for the compasscompensating coils is the voltage-dropacross a fixed resistor connected in serieswith the degaussing coil or, for newerequipment, a voltage source from therespective coil degaussing power supply.This voltage and the current that the powersupply sends through the compass compen-sating coils are proportional to the degauss-ing coil current. This is the condition whichmust be satisfied to ensure that the com-pass compensation will not be disturbed bya change in the degaussing coil current.

475-8.1.8 CONTROL BOXES. Onetype A or type A-1 control box is used foreach degaussing coil that requires compasscompensation. The control box consists of awatertight enclosure with a removablecover and contains three sets of resistors.One is used for compensating the H (Heel-ing) component and two for the horizontalcomponents, NE and NW.

Figure 475-8-3. Type K-2 Compen-sating Coil Assembly

and Type A-1Control Box.

475-8.1.8.1 Type A and Type A-1Control Box Wiring Diagrams.Figures 475-8-4 and 475-8-5 show type Aand type A-1 control box wiring diagrams,respectively. The current in a compasscompensating coil winding is adjusted,when the compass is compensated fordegaussing, by adjusting the variable resis-tors (shorting out one or more of the fixedresistors in the case of the type A box).

475-8.1.8.2 Type K-2 and Type R-2Compass Coils Wiring Diagrams.Wiring diagrams for type K-2 and type R-2compass compensating coils are shown infigures 475-8-6 and 475-8-7, respectively.Similar diagrams are in the compass com-pensating coil manual. See NAVSEA 0924-LP-044-7010, Compass CompensatingCoil Type K-2, or NAVSEA 0924-LP-044-9010, Compass CompensatingCoil Type R-2.

S9086-QN-STM-010/CH-475

8-4

TABLE 475-8-1. STANDARD TYPES OF COMPASS COMPENSATING COILS

Type Use

K-2 This is the latest type of general purpose compass com-pensating assembly coil. This type should be used innew installations and for replacement of earlier type "K"coils that are removed because they are defective orshow signs of impending failure. Type "K-2" fits USNStandard Mark VII binnacle, USN standard No. l shelf-type binnacle and all types of binnacles on merchantships built for the U.S. Maritime Commission in WorldWar II. The type "K-2" assembly is interchangeablewith the "K-1" and "Filled K" types. See figure 475-8-3for type "K-2" assembly and associated type "A-1" con-trol boxes installed on a Navy Standard Mark VII bin-nacle.

R-2 The type R-2 compass compensating coil is used for com-pensation of the USN No. 5 boat compass, the USN No.3 compass, the gyro fluxgate compass, and the modifiedMagnesyn compass. When used to compensate the No.3 compass, the coil is supported by brackets or collars toaccommodate special compass mounting, as installed inthe FF’s pilot house, for example.

475-8.2 INSTALLATION AND COM-PASS COMPENSATION

475-8.2.1 INSTALLATIONPERSONNEL. Compass compensat-ing coils are usually installed by navalshipyard personnel or degaussing activity,not by the ship’s force. If it is ever neces-sary for the ship’s force to install the com-pass compensating coils, the installationshould be made in accordance with the in-struction manual furnished with the coils.

475-8.2.2 COMPASS COMPEN-SATION PERSONNEL. Compassesare usually compensated for degaussing bypersonnel at a naval shipyard or a degauss-ing activity. At times, however, the ship’sforce may have to compensate the com-passes after repairs to the compass compen-sating coil installation. For this reason, in-structions on compass compensation are in-cluded, beginning in paragraph 475-8.2.5.

475-8.2.3 DOCKSIDE COMPEN-SATION LOCATION. Dockside com-pensation is a preliminary compensationusually made soon after the degaussing sys-tem is installed and tested. Dockside com-pensation is made while the ship is moored.The compass is deflected with one degauss-ing coil at a time turned on, and the ap-propriate control resistor is adjusted so thatthe compass error caused by the degaussingcoil is a minimum. (See paragraph475-8.2.3.1 for further discussion of dock-side compensation.)

475-8.2.3.1 DOCKSIDE COMPEN-SATION CONDITIONS. Certainconditions must be dealt with during dock-side compensation. Local magnetic distur-bances caused by moving cranes, movingships alongside, arc welding, and other ac-tivities may impair the accuracy of docksidecompensation. Dockside compensationshould be made, if possible, when distur-bances are at a minimum (during the noonhour or at changes of shifts). Maximum coil

S9086-QN-STM-010/CH-475

8-5

Figure 475-8-4. Type A Control Box Wiring Diagram.

currents specified in the ship’s degaussingfolder should be used during dockside com-pensation.

475-8.2.3.2 Optimum DocksideCompensation. Better dockside com-pensation will result if the compass is ingood normal adjustment. If the compass isnot in good normal adjustment, normal ad-justment should be approximated. If nor-mal adjustment or a partial adjustmentcannot be made, the dockside compensationshould still be made, since even under poorconditions the dockside compensation givesa check on correct voltage supply, electricalconnection and winding polarity. Whendockside compensation is made under goodconditions, only slight or no resetting of thecontrol resistors will be required in the finalcompensation.

475-8.2.4 FINAL COMPENSATIONLOCATION. Final compensation ismade in the harbor or swinging area oncompletion of normal compass compen-sation (magnets, spheres) with the shipaway from dockside disturbances. It is arefinement of the dockside compensation.

475-8.2.5 COMPASS COMPENSA-TION TECHNIQUE. Compass com-pensation for degaussing consists of adjust-ing resistors in the control boxes so that thecompass points in the same directionregardless of whether the degaussing coilsare turned on or off.

475-8.2.6 FINAL COMPENSATIONTECHNIQUE. Final compensation ismade by placing the ship on the desiredheading and then, with one degaussing coilat a time turned on, adjusting the ap-propriate control resistor so that the com-pass error caused by degaussing is at aminimum. Both dockside and final compen-

S9086-QN-STM-010/CH-475

8-6

Figure 475-8-5. Type A-1 Control Box Wiring Diagram.

sation should be made only by qualified ad-justers.

475-8.2.6.1 Swing for Deviation.Immediately following final compensation,the ship is swung to determine compassdeviations.

475-8.2.6.2 Intercardinal Coil Com-pensation Headings. Intercardinallymounted compass coils are compensated onintercardinal headings; that is, with thecompass reading NE or SW for compensat-ing the NE component, and NW or SE forcompensating the NW component. Theheadings used are positioned so that thecompass needles are perpendicular to thecomponent of the degaussing coil magneticfield being compensated. The heeling coilcan be compensated on any heading.

475-8.2.6.3 ComponentCompensation. The H (heeling) com-ponent should be compensated first, thenthe horizontal components. The followingprocedure should be used for compensatingthe H (heeling) component for both car-dinally and intercardinally mounted com-pass coils.

475-8.2.6.4 Reduction of ResidualMagnetism by Reversals. Startwith all the degaussing coil currents set atthe maximum current specified in thedegaussing folder. Then reduce all coil cur-rents to zero by the method of reversals, asfollows:

a. Reduce the current to zero and thenincrease it to the starting value in thereverse direction.

b. Reduce the current to zero and thenincrease it to 3/4 value in the original direc-tion.

S9086-QN-STM-010/CH-475

8-7

Figure 475-8-6. Type K-2 Coil Wiring Diagram.

S9086-QN-STM-010/CH-475

8-8

Figure 475-8-7. Type R-2 Coil Wiring Diagram.

S9086-QN-STM-010/CH-475

8-9

c. Reduce the current to zero and thenincrease it to 1/2 value in the reverse direc-tion.

d. Reduce the current to zero and thenincrease it to 1/4 value in the original direc-tion.

e. Reduce the current to zero and thenincrease it to 1/8 value in the reverse direc-tion.

f. Reduce the current to zero.

475-8.2.6.5 CompensationAdjustments. After reducing the coilcurrents to zero by the method of reversals,compensate the compass as follows:

a. Remove the compass and put in acalibrated dip needle in place of the com-pass. For model A Magnesyn transmitters,the dip needle pivot should be centered be-tween 5/8 and 7/8 inch above the top of thecompass coil. For model B Magnesyn trans-mitters, the distance should be between2-7/8 and 3-1/8 inches. For other com-passes, center the dip needle at the level ofthe compass card.

b. Adjust the weight on the dip needleto make the needle horizontal. If theweight on the dip needle was previously setfor normal compass adjustment and it isdesired to leave this setting undisturbed,level the needle by raising or lowering theheeling magnet. If the second method isused, make sure that the heeling magnet isrestored to its correct position after compen-sating the H-component of the degaussingcoil field. In certain cases, it may not beconvenient to replace the compass with adip needle. Under this condition, otherprovisions, such as placing the dip needle toone side of the compass compensating coilat a predetermined location, may be neces-sary.

c. Energize one degaussing coil with itsmaximum current and note any dip of theneedle. If the needle does not dip, steps dand e are unnecessary.

d. Increase or decrease the current inthe heeling coil circuit for the energizeddegaussing coil to make the dip needlereturn to its original position. This maynecessitate shorting out or adding fixedresistance as well as adjusting the variableresistor, or it may require reversing thecompensating coil leads. Note the dip withand without the heeling coil in the circuit tosee whether the heeling coil leads need tobe reversed. The heeling coil leads shouldbe reversed if the needle dips more in thesame direction when the heeling coil is inthe circuit.

e. Check the current through the com-pass compensating coils and the variableand fixed resistors of the control box tomake sure that the current in each circuitelement does not exceed the current ratingof the element.

f. Reduce the degaussing coil current tozero and then increase it to the maximumvalue in the opposite direction. Note anydip in the needle, other than a momentarydip, and make any further adjustmentsnecessary.

g. Reduce the degaussing coil current tozero by the method of reversals (seeparagraph 475-8.2.6.4).

h. Repeat steps c through g for eachdegaussing coil.

i. Record the compensation data, as it istaken, on NAVSEA Form 8950/40,Compass Compensating Coil Data,(figure 475-8-8).

475-8.2.6.6 Deflecting Compass forHorizontal Components. The head-ing of the ship is unchanged during dock-side compensation. Instead, a suitable ar-rangement of deflector magnets is employedto deflect the compass to specified readingsand to approximate the strength and direc-tion of the magnetic field that would bepresent if the ship were placed on the head-ing that corresponds to the compass read-ing.

S9086-QN-STM-010/CH-475

8-10

Figure 475-8-8. Compass Compensating Coil Data, NAVSEA Form 8950/40.

S9086-QN-STM-010/CH-475

8-11

475-8.2.6.7 Deflecting MagnetPlacement. To deflect the compass bymeans of a permanent magnet (or a bundleof magnets), the deflecting magnet shouldbe placed with the longitudinal axis perpen-dicular to the imaginary vertical plane thatbisects the angle between the original direc-tion of the compass needle and the desireddirection. The magnet may be placed eitherabove (preferred), to the side, or below thecompass, provided that the axis of the mag-net is perpendicular to the bisecting plane.The desired compass heading is obtained bymoving the magnet closer to or fartheraway from the compass. Figure 475-8-9 il-lustrates this method of deflecting the com-pass.

475-8.2.6.8 NE and NW ComponentCompensation. The compensatedhorizontal components are the NE and theNW components for intercardinallymounted coils. The larger componentshould be compensated first.

475-8.2.6.9 NE Component. Thefollowing procedure should be used to com-pensate the NE component:

a. Replace the dip needle with theregular compass.

b. Deflect the compass to a reading of045 or 225 (paragraph 475-8.2.6.7).

c. Energize one degaussing coil with itsmaximum current and note the compassdeflection. If the compass does not deflect,steps d and e are unnecessary for thisdegaussing coil.

d. Increase or decrease the current inthe labeled NE compensating coil windingfor the degaussing coil being compensatedto make the compass return to the headingobtained in step b. This may require short-ing out or adding fixed resistors as well asadjusting the variable resistor in the con-trol box. It may also require reversing thecompass compensating coil leads. To see if

the coil leads need to be reversed, note thecompass deflection with and without thecompensating coil in the circuit. Reversethe leads if the deviation with the coil inthe circuit is in the same direction andlarger than when the coil is not in the cir-cuit.

e. Check the current through the coiland the variable and fixed resistors in thecontrol box to make sure that the current ineach circuit element is no greater than thecurrent rating of the element.

f. Reduce the degaussing coil current tozero and then increase it to a maximum inthe other direction. Note any deviation andmake any refinement necessary.

g. Reduce the degaussing coil current tozero by reversals (paragraph 475-8.2.6.4).

h. Repeat steps c through g for eachdegaussing coil.

i. Record the compass compensationdata, as it is taken, on NAVSEA Form8950/40, Compass Compensating CoilData (figure 475-8-8).

475-8.2.6.10 NW Component. Theforegoing procedure for compensation of theNE component is repeated for compensationof the NW component, except that the com-pass is deflected in step b to a reading of135 or 315 and the current adjusted in thelabeled NW compensating coil winding.

475-8.2.6.11 Check for ResistorSettings. A major change of the cur-rent in one compass coil winding willchange the voltage drop in the compass coilpower supply leads and will change thevoltage applied to the other compass coilwindings. When one or more compasses arebeing compensated, all coils of all com-passes should be approximately compen-sated before making the final resistor set-tings. If only one compass coil is installedaboard the ship, resistor settings may bemade immediately after compensation be-

S9086-QN-STM-010/CH-475

8-12

Figure 475-8-9. Deflecting Compass With Permanent Magnet.

cause there are no other coils to be adjustedand no possibility of disturbing the adjust-ment of the single coil.

475-8.2.6.12 Check for Residuals.With the compass deflected to a reading ofabout 090 or 270, energize a degaussing coilwith its maximum positive value, thendeenergize without reversals. If the com-pass fails to return to within 1 degree of itsoriginal reading, that particular degaussingcoil should be secured by a series of rever-sals explained in paragraph 475-8.2.6.4.Each degaussing coil should be checked forresiduals for both positive and negative coilcurrent, and the results shall be indicatedper paragraph 475-8.2.6.13.

475-8.2.6.13 Securing by ReversalDocumentation. If a coil should re-quire securing by reversals, this fact shouldbe noted on NAVSEA Form 8950/40,Compass Compensating Coil Data(figure 475-8-8), by an entry underRemarks and on NAVSEA Form 3120/4,Magnetic Compass Table (figure475-8-10), by inserting the designations of

the coils that should be cycled (secured byreversals) (width of figure 475-8-10 is over-sized for clarity).

475-8.2.6.14 Final Compensation.Final compensation is a refinement of dock-side compensation and is made under ac-tual operating conditions away from dock-side magnetic disturbances and after afairly accurate normal compass adjustment.Final compensation is made in the sameway as dockside compensation except that adeflecting magnet is not used to deflect thecompass needle to the desired reading. In-stead, the ship itself is placed on the head-ing that gives the compass reading desiredfor compensation.

475-8.2.7 ACCURACY.Compensation should reduce compassdeviations to as small a value as possible.The deviation shall be reduced to 2 degreesor less, and the heeling effect reduced to adegree so small that it will not cause oscil-lation in a heavy sea with the degaussingcoils on. In some cases, however, where theinitial horizontal deviations are large (30 to

S9086-QN-STM-010/CH-475

8-13

Figure 475-8-10. Magnetic Compass Table, NAVSEA Form 3120/4. (Sheet 1 of 2)(shown oversize for clarity)

S9086-QN-STM-010/CH-475

8-14

Figure 475-8-10. Magnetic Compass Table, NAVSEA Form 3120/4. (Sheet 2 of 2)(shown oversize for clarity)

S9086-QN-STM-010/CH-475

8-15

60 degrees), it may be impractical to reducethese deviations to the 2-degree value. Insuch cases, the deviations can always bereduced to less than 10 percent of theoriginal deviation and normally can bereduced to less than 7 percent of theoriginal deviation.

475-8.2.8 ASYMMETRICALDEVIATIONS. Asymmetrical mag-netic fields, due either to the compass mag-nets or to the compass coils, may, under un-usual conditions, result in asymmetricaldeviations that cannot be reduced to thelimits specified above. Asymmetrical devia-tions occur on headings that differ fromthose used for the setting compass coil cur-rents and therefore cannot be compensatedby resetting these currents. In the case ofcardinally mounted compass coils, unsym-metrical deviations are maximum on head-ings other than N/S or E/W and for inter-cardinally mounted coils, are maximum onheadings other than NE/SW or NW/SE.

475-8.2.8.1 Asymmetrical DeviationCompensation Technique.Asymmetrical deviations may be reduced tothe limits specified above by:

a. Replacing the compass coils with amodern assembly of known symmetry.

b. Replacing the magnetic compasswith one of known symmetry.

c. Relocating the binnacle to a positionfarther from the degaussing cables.

d. Relocating the degaussing coil cross-over to a position farther from the binnacle,if such relocation will maintain an equallysatisfactory magnetic signature.

475-8.2.8.2 Binnacle PositionCheck. A check to determine whetherthe binnacle is too close to the degaussingcables can be made by using the followingformula.

D =NI200

where:

D = distance in feet

NI = total ampere turns in thedegaussing cables

475-8.2.9 BINNACLE POSITIONOUT OF TOLERANCE. If theseparation between the compass and thedegaussing cables is less than that obtainedby the formula, the condition should bereported to the nearest Naval shipyard.See NSTM Chapter 252, Ship ControlEquipment, for further data.

475-8.2.10 PRECAUTIONS. Caremust be taken to see that the safe currentsof the resistors and compensating coils arenot exceeded in both dockside and finalcompensation.

475-8.2.10.1 Maximum Currents,Type A Control Box Resistors.Resistors in the type A control box may beconnected in various parallel and seriescombinations provided that the maximumcurrents do not exceed:

a. 25-ohm variable resistor - 1.41 am-peres.

b. 50-ohm fixed resistor - 1.00 ampere.

c. 150-ohm fixed resistor - 0.58 ampere.

d. 400-ohm fixed resistor - 0.35 ampere.

475-8.2.10.2 Maximum Currents,Type A-1 Control Box Resistors.Maximum currents in the type A-1 boxresistors should not exceed:

a. 15-ohm variable resistor - 2.00 am-peres.

S9086-QN-STM-010/CH-475

8-16

b. 1-ohm variable resistor

260-ohm portion - 0.32 ampere

40-ohm portion - 1.25 amperes.

475-8.2.10.3 Maximum Coil Cur-rents, Type K, K-1, K-2, R-1 and R-2Coil Types. Maximum current in anyone winding of a compensating coil shouldnot exceed the value given in table 475-8-2.

TABLE 475-8-2. COIL MAXIMUMCURRENT IN ANY

ONE WINDING

Type of Coil

MaximumCurrent

(amperes)

K, K-1, K-2,and Filled K:

NE and NW coilsHeeling coil

1.42.0

R-1 1.0

R-2 1.0

475-8.2.11 FORWARDING OFFORMS. For specific instructionsregarding forwarding NAVSEA Form3120/4, Magnetic Compass Table, referto NSTM Chapter 252, Ship ControlEquipment. A copy of NAVSEA Form8950/40, Compass Compensating CoilData, should be filed in the installation sec-tion of the degaussing folder. One copy ofthe form should be forwarded to NAVSEAat the time of the initial compensation andupon any subsequent compensation madeas a result of adding additional compensat-ing equipment or changing the type ofequipment. In the case of changing or ad-ding equipment, the form will normally bemade out by the installing activity. Theform should be submitted by the ship’s forceif it performs the compensation.

475-8.3 OPERATION

When the degaussing coils are energized,the compass compensating coils operateautomatically. Operation should bechecked at least once a week by notingwhether any compass deviations, in excessof the allowable limits (paragraph475-8.2.7), are caused when power to thedegaussing coils is turned on or off.

475-8.4 MAINTENANCE

There are several common sources of trou-ble for the various components of the com-pass compensating system.

475-8.4.1 COMPASS COMPENSAT-ING COILS. Care should be takenthat the position of the coils on the binnacleis unchanged. Grounds and resultant burn-outs of the windings may be caused whencoil case seams are broken because of mech-anical damage or improper installation. Aninsufficient number of shims used betweenthe coil and the binnacle and subsequenttightening of the coil mounting bolts maydistort the case and break the solderedseams. Leaky packing glands and gasketsmay also allow moisture to enter the casewith resulting grounds. An increase indegaussing deviation may be caused by alack of recompensation of compass compen-sating coils after alterations to the degauss-ing coils or after changes in the ship’s steel.

475-8.4.2 CONTROL BOXES.Grounds, poor electrical connections, cor-rosion of resistors, and burn-outs of wind-ings and resistors may be caused by theentrance of moisture into type A or A-1 con-trol boxes. This moisture is usually theresult of loose covers or leaky gaskets orstuffing tubes. When grounds are isolatedin the compass compensating system, thecontrol box involved should be opened and,if wet, should be drained and dried out.

S9086-QN-STM-010/CH-475

8-17

475-8.4.2.1 Control Box Mainte-nance Procedure. All corrosionshould be cleaned from the resistor contactsand, if beyond repair, the entire resistor as-sembly should be replaced. Cable shouldenter exposed control boxes on the bottomor on the sides, not on the top. Whererepeated grounds occur in a four-lug controlbox mounted in the weather, the entire unitshould be replaced with a six-lug controlbox and in addition, where practical,mounted out of the weather.

475-8.4.2.2 Connecting Cables.Cable from the compass coils to the controlboxes should be checked for possible cracksin the sheath or for mechanical damage. Ifcable is run through a deck, suitable protec-tion should be afforded by kick pipes. Itshould be watertight where nipples enterthe control boxes.

475-8.4.2.3 Reports. Report allequipment failures and replacements in ac-cordance with the Planned MaintenanceSystem.

475-8.4.2.4 Compass CoilTroubleshooting. The followingsteps should be followed when troubleshoot-ing the compass coil electrical equipment:

a. Check each winding for short circuitsand continuity. (Use an ohmmeter at thecontrol box.)

b. Test each winding for magnetic effectand identity. (Use 1-1/2 volt flashlight bat-tery across the winding leads in the controlbox. Explore, with a pocket compass, for ef-fect of winding.) Make sure the windings inseries aid in magnetic polarity. Make sureeach winding is connected to the propercontrol circuit and tagged.

c. Test the insulation resistance be-tween the compensating coil windings andfrom each winding to ground with a meg-ger.

d. Make sure the control resistor con-tacts and terminals are not corroded. In-spect the cover and terminal tubes forleakage if corrosion exists.

e. Check the supply voltage to the con-trol box; it should be proportional to thedegaussing circuits. The best results areobtained when the supply voltage into thecontrol box is between 6 and 10 volts with 3amperes load current and the degaussingcurrent set at the maximum value specifiedin the degaussing folder.

f. Make sure each compass compensat-ing effect is strong enough to compensatethe degaussing effect.

g. Make sure the winding current doesnot exceed the maximum current valuesgiven in table 475-8-2.

475-8.4.2.5 Locating Grounds. Ifa ground appears in the compass coil cir-cuits:

a. Open the type A or type A-1 compasscompensating coil control box for thedegaussing coil circuit grounded.

b. Disconnect the compass compensat-ing coil feeder from the degaussing circuit.Check both conductors of the feeder forgrounds.

c. If a grounded reading is obtainedhere, disconnect the feeder at the other endto isolate the ground in either feeder con-ductor.

d. If the feeder to the type A control boxis not grounded (see figure 475-8-4):

1. Isolate the circuits compensatingthe degaussing coil being checked by discon-necting the jumpers (if installed) parallel-ing the A terminals in the control box andalso the jumper paralleling the B terminals.

2. Check the insulation resistancefor each compass coil circuit to the groundby connecting a meter between terminal Aor B and the ground.

S9086-QN-STM-010/CH-475

8-18

3. After finding the grounded circuit,ascertain whether the ground is in the com-pass resistors or in the compass coil wind-ing by disconnecting the compass coil wind-ing at terminals CCC-B and CCC-O-25C inthe control box.

4. In the event the winding isgrounded and the coil is otherwise satisfac-tory, physically and electrically, substitutethe spare winding of the same coil, if avail-able. This substitution will require check-ing the compensation and recompensationas necessary.

5. If the ground is located in theresistor bank of the type A or type A-1 con-trol box and is due to moisture, wipe thebox clean and dry it by means of exposureto sunlight or the heat of an electric lightbulb. Check for the entrance of moisturedue to a distorted box cover, improperlyseated gasket, or leaky terminal tubes.

e. If the feeder to the type A-1 controlbox is ungrounded, use figure 475-8-5 and aprocedure similar to the item d list above.

S9086-QN-STM-010/CH-475

A-1

APPENDIX AREFERENCE PUBLICATIONS

The following technical publications are listed in the order in which they appear in the text:

Section 1

NSTM Chapter 300, Electrical Plant General

Section 2

OPNAVINST 5100.19, "Navy Occupational Safety and Health (NAVOSH) ProgramManual for Forces Afloat"

Section 3

MIL-I-631, Insulation, Electrical, Synthetic-Resin Composition, Non-rigid

Section 5

NAVSEA 0967-LP-000-0160, Electronics Installation and Maintenance Book

NAVSEA S9475-AF-OMI-010, Degaussing Manual

Section 6

NAVSEA S9475-AC-PR-010, Degaussing Forms, Records, and Reporting Procedures

OPNAVINST C8950.2, Magnetic Silencing

Section 7

NAVSEA S5475-AC-MMM-010/(C), Magnetic Ranging and Calibration of DegaussingSystems - Degaussing Performance Criteria

MIL-STD-2036, General Requirements for Electronic Equipment, Specifications

S9086-QN-STM-010/CH-475

A-2

SSP Instruction 8950.2, "Procedures for Protection of FBM/Strategic Weapon Sys-tem Components During Flash Deperm Treatment of SSBN 598, 608, 616, (616-659including the C-4 Backfit Configurations), and 726 Class (TRIDENT) Submarines"

NAVSEA 0324-LP-047-7010 through 7120, Technical Manual for SINS MK 2 MOD 1

NAVSEA 0324-LP-064-5101 through 5620, Technical Manuals for SINS MK 3 MOD 5

NAVSEA 0924-LP-001-2010 through 2120, Technical Manuals for SINS MK 3 MOD 5




NSTM Chapter 074, Welding and Allied Processes

NSTM Chapter 541, Petroleum Fuel Stowage, Use and Testing

Section 8

NAVSEA 0924-LP-044-7010, Compass Compensating Coil, Type K-2

NAVSEA 0924-LP-044-9010, Compass Compensating Coil, Type R-2

NAVSEA Form 8950/40, Compass Compensating Coil Data

NAVSEA Form 3120/4, Magnetic Compass Table

NSTM Chapter 252, Ship Control Equipment

S9086-QN-STM-010/CH-475

Glossary-1

GLOSSARY

Alternating electric (AE) fields - the electric field component of an electromagnetic fieldwhose magnitude varies with time, whether periodically or aperiodically.

Alternating magnetic (AM) field - the magnetic field component of an electromagnetic fieldwhose magnitude varies with time, whether periodically or aperiodically.

Ammeter calibration - Checking of remote control unit ammeters on steel-hulled ships toverify that they have been calibrated (see equipment manual for procedure).

Ampere turns - the product of the current in a coil or loop and the number of effective turns.

Beam - the extreme molded width of the ship hull at the widest part.

Calibration limit - the maximum acceptable value of the magnetic flux density after theonboard degaussing system has been calibrated or the ship/submarine has beenflashed/depermed.

Check ranging - The action of a ship making reciprocal range runs for the purpose of satis-fying the measurement of the component of the static magnetic (SM) field signaturemeasurement requirements.

Check range limit - the maximum acceptable value of the magnetic signature. The mag-netic signature is determined when the ship/submarine runs a magnetic silencing range.

Coil section - A section of a degaussing coil cable is the length of cable between two succes-sive connections or through boxes.

Compass compensation coil assemblies - Coil assemblies that, when energized with directcurrent, create a magnetic field approximately equal and opposite to the degaussing field atthe compass, thereby eliminating the undesirable effects of degaussing upon the compass.

Compass compensation coils check - The contractor shall demonstrate operation of thedegaussing compass compensating circuits on steel hull ships by performing a docksidedegaussing compass compensation, before builder’s trial, of each magnetic compassequipped with a compass compensating coil. All data required for form, 8950/40 (CompassCompensating Coil Data), shall be noted and recorded on the form during this compen-sation.

Compass compensating control box - A watertight enclosure having a removable cover andcontaining sets of control resistors. By adjustment of the control resistors, the compasscompensating coil currents are regulated to give the desired magnetic compass compen-sation.

S9086-QN-STM-010/CH-475

Glossary-2

Components of magnetism - magnetism, both permanent and induced, is composed of ver-tical, longitudinal, and athwartships components.

Conductor turn - One conductor encircling the loop area once.

Connection box - A watertight box with a removable cover used as a junction to connectloops together, to connect conductors in series, to reverse turns, and to perform similarfunctions. The power supply connection for a coil and adjustments of ampere turn ratiosbetween loops are made within connection boxes.

Degaussing - The technology dealing with the methods and techniques of reducing a ship’sstatic magnetic (SM) field with onboard coils.

Degaussing coil - One or more loops of degaussing cable where each loop encircles a dif-ferent total area. A degaussing coil provides compensation for the ship’s magnetization ineither the vertical , longitudinal, or athwartship direction.

Degaussing control and power equipment - Equipment that produces the degaussing cur-rents and contains electrical circuits, indicating devices, and controls to provide automaticand manual control of the polarity and magnitude of the degaussing coil currents.Automatic control is provided as a function of the earth’s magnetic field along the ship’saxes.

Degaussing folder - The degaussing folder, form NAVSEA 8950/1, is an official ship log. Itcontains instructions for operation of the degaussing system, degaussing charts, values forcurrent and turn settings, installation forms, compass compensation forms, and a log sec-tion showing all pertinent details of magnetic treatment and of action taken on the ship’sdegaussing system for the information of degaussing authorities. The degaussing folder isissued to a ship by the Magnetic Silencing Facility that renders the initial magnetic treat-ment and system calibration.

Degaussing system - Consists of control and power equipment and one or more coils ofelectric cable installed at specific locations on board ship to reduce the ship’s magnetic sig-nature. In operation, these coils are energized with direct current so that the magneticfield produced is in opposition to, and reduces, the magnetic field of the ship. Equipment isprovided to vary the current through the coils in both magnitude and polarity. Thedegaussing system also includes the compass compensation equipment.

Effective turns - The number of turns that are effective in producing a magnetic field underthe ship. The difference between the number of series conductors in a loop in which thecurrent is in a counterclockwise direction (called forward turns) and the number of seriesconductors in which the current direction is clockwise (called reverse turns), when viewedin accordance with polarity convention for each coil.

Induced magnetism - That component of the ship’s magnetic field that results from theship’s position in an external magnetic field. This component varies as a function of theship’s location, heading, roll, and pitch in the earth’s magnetic field.

S9086-QN-STM-010/CH-475

Glossary-3

Installation information forms - Installation information forms are official NAVSEA formsshowing plan and profile views of degaussing coils (steel hull ships only), identification ofequipment, schematic electrical diagrams, test results, and other pertinent information onthe system as installed.

Just above a deck - Where cables are specified to run "just above a deck" the cable is in-stalled, unless otherwise noted, to allow a 4-1/2 inch clearance between the deck and thebottom of the cables.

Just under or below a deck - Cable is strapped to supports mounted directly to the deck sothat the cable will be flush with overhead. Where athwartship beams and brackets areencountered, the cable is routed around or through the beams or brackets. Cables runningathwartship are strapped underneath deck plating or along the beams, depending on thespecified location and interferences encountered for installation.

Just within the skin or shell - The cable is routed and strapped along the inboard side ofthe transverse frames to which the plates or planks forming the "skin" or shell of the shipare fastened. The cables are run through the webs of deep frames if ample strength com-pensation is made where the webs are pierced. Cables are not run more than 18 inchesinboard of skin.

Loop - One or more turns of the conductors of a degaussing cable encircling a specific area.All loops that produce fields along a particular ship’s axis for a coil. In steel-hulled shipsdifferent loops connected in series form a degaussing coil; for example: FI-1, FI-2, QI-1 loopsare connected in series to form an FI-QI coil. To conserve cable, the conductors used fordifferent loops encircling the same area may be contained in the same cable; for example:an FP and FI loop may both be contained in an FI-FP designated cable.

Magnetic silencing - Any method or procedure that will reduce the magnetic/electric sig-nature of a ship or submarine.

Magnetic silencing methods - Magnetic Treatment

a. Deperming - The process whereby a ship’s permanent longitudinal and athwartshipmagnetism is ideally removed and its vertical permanent magnetism is stabilized at aknown level by exposing the platform to large magnetic fields of alternating polaritiesand decreasing magnitude.

b. Flashing - a deperming treatment used on ships and submarines with no shipboarddegaussing coils. In this treatment, the vessel’s permanent vertical magnetism ischanged in such a way that the total magnetization will be at a minimum in its in-tended area of operation.

Magnetic Types:

1. Permanent - The magnetism resulting from a ship or submarine being built in thepresence of the earth’s magnetic field and other fields such as those produced bywelding cables, electromagnetic positioners, magnaflux testers, engine starting

S9086-QN-STM-010/CH-475

Glossary-4

cables, etc. The magnitude is determined by the location of the building facility, theorientation of the hull with respect to the earth during construction and thematerial used for construction and its magnetic history. The permanent magnetismwill change slowly through platform vibration, change in geographic location, exten-sive period on a single heading, etc.

2. Induced - Magnetism that results from a ship or submarine operating in the earth’smagnetic field. The magnitude is determined by the ship/submarine geographicposition and attitude (heading, roll, and pitch) with respect to the direction of theinducing field.

Magnetic/electric fields - For the purpose of this instruction and other definitions, theship/submarine magnetic or electric field sources are stationary with respect to the mag-netic or electric field measurement sensor.

Magnetometer interference tests - Tests performed if a magnetometer is installed. Mag-netometer interference tests are performed to determine if various items of ship equipmentmight materially affect the magnetic field in the vicinity of the magnetometer probe. Themagnetometer outputs are monitored to observe changes in readings caused by operation ofother equipment. The Supervisor shall be notified of interferences greater than0.2 microtesla. Notification shall include source and magnitude of the interference.

Magnetometer probe assembly - A unit that is a magnetometer or part of a magnetometerthat is installed remote from the degaussing control unit.

Middle-fifth - The middle 1/5 of the length of the ship.

Modification forms - Modification forms are official NAVSEA forms describing all modifica-tions to the degaussing system during calibration, repair or conversion.

Parallel circuit - An arrangement of conductors connected to provide two or more completeand independent electrical paths through a coil or loop and having a common source ofsupply.

Permanent magnetism - That component of the ship’s magnetic field that is permanentlyfixed in the ship’s ferrous structure. This component changes as a result of mechanicalstress, vibration, or deperming and is likely to change during a major overhaul or conver-sion period.

Remote control unit - A unit that enables an operator to monitor coil currents and manuallyinput heading changes during manual operation.

Run - The continuous route of the cable (including connection and through boxes) betweenspecified elevations, distances, or frames.

S9086-QN-STM-010/CH-475

Glossary-5

Satisfactory check range - Two range runs on reciprocal headings within a six-week periodthat are determined to be magnetically satisfactory (i.e., meet the check range limits whileship-installed degaussing equipment is operating properly).

Static electric (SE) field - An electric field whose magnitude remains constant with time.

Static magnetic (SM) field - A magnetic field whose magnitude remains constant with time.

Tesla (T) - The Systeme Internationale (SI) unit used to denote the magnitude of magneticflux density. It is the preferred unit and is to be used in all correspondence and publica-tions on this subject. Nanotesla may be used when discussing magnetic signatures of ships;microtesla should be used when discussing the earth’s magnetic field. The following con-version list is provided for convenience:

1 tesla (T) = 10,000 gauss (G)1 millitesla (mT) = 10 gauss (G)1 microtesla (µT) = 0.01 gauss = 10 milligauss (mG)100 nanotesla (nT) = 0.001 gauss = 1 milligauss (mG)1 nanotesla (nT) = 0.01 milligauss = 1 gamma

Through box - A watertight box with a removable cover used to connect sections of cablewithout changing the order of conductor connections.

Turns - One complete lap around the perimeter of a specified area by a coil or loop. Oneturn consists of one conductor or two or more conductors connected in parallel.

S9086-QN-STM-010/CH-475

Glossary-6

THIS PAGE INTENTIONALLY LEFT BLANK

2

2

2

Documents

FIRST REVISION NAVAL SHIPS’ TECHNICAL MANUAL S9086 …