Piloting Course Chapter 4 On-the-Water United States Power Squadrons ®

Piloting Course Chapter 4

On-the-Water

United States Power Squadrons ®

Slide 2

Responsibilities of the Skipper

You are responsible for the safety of• Your crew• Your boat

Consequently, you decide on navigation• Use the techniques that ensure your safety

The Piloting Course provides the tools• It’s up to you to decide how to apply them

Slide 4

View from the Water

Learn to recognize ‘on-the-water’ views• Navigation Aids• Landmarks• Land Features

Study charts so you know what to look for

Practice on clear days so you know the landscape when it turns foul

Slide 5

Use GPS as Primary Position Sensor

Properly Set Up GPS• Chart Datum -- WGS 84 (or other as

required)• Latitude & Longitude (grid)

Degrees, Minutes, Tenths of Minutes for most coastal charts

Degrees, Minutes, Seconds for many inland charts

• Magnetic reference (preferred, auto set)

• Nautical Units Matches the chart (coastal)

– Nautical Miles (nm) & Knots (kn) Statute units (Great Lakes and inland charts)

– Statute Miles (mi) & Miles per Hour (mph)

Slide 6

Use the Compass for Steering

GPS is NOT a compass• It provides direction based on movement

history• Will not work in static situation

Compass is easier to steer with• May need to use GPS to get oriented• Then, read and follow the compass heading

Slide 7

Attributes of a Quality Compass

Repeatability• Always returns to the same reading• When, returned to the same heading

or, when temporarily diverted using a magnet or metallic object

Damping• Turns smoothly on your boat• Sail & Powerboat compasses are

different

Largest you can afford• Easier to read, smoother movement• Top Reading, preferred

© 2003, R J Sweet, “GPS for Mariners.” Reprinted with permission© 2004, “The Weekend Navigator”

Slide 8

Ship’s Compasses

Courtesy: Ritchie

Front Reading

Top Reading


Slide 9

Sailboat Compasses

Courtesy: Ritchie

Top Reading Bulkhead Mounted

Angle of Heel

Sailboat compasses have differentDampening than powerboat compasses


Slide 10

Hand Bearing Compasses

Courtesy: Ritchie, Davis, Plastimo


Slide 11

Compass Binoculars

Slide 12

Errors Affecting Compasses

Metallic Objects• Alter local magnetic fields• Can cause compass errors

Current-carrying Wires• Create their own magnetic fields• Interfere with Earth’s field near

compass

Compass Error – called DEVIATION• Dependent upon heading of boat• How to Measure – Appendix B

The boat’s effect on the compass…


Slide 13

Boat Effects on Compass

In one direction the metallicmass may have little effect on the local magnetic field

In another direction the metallicmass may have a much greatereffect on the local magnetic field

Slide 14

DEVIATION

Compass can be adjusted• Counteract local deviation using • Compensating magnets in compass

Compass Adjusting• Recommend a professional adjuster

Residual Deviation• Even after compensation – some

deviation• May need to correct compass readings to

magnetic (or vise-versa)

Slide 15

Deviation Table

Table of Corrections

Deviation Table

Magnetic to Compass Compass to Magnetic

Magnetic Degrees

Deviation Degrees

Magnetic Degrees

Deviation Degrees

Compass Degrees

Deviation Degrees

Compass Degrees

Deviation Degrees

000° 1°W 180° 0° 000° 1°W 180° 0° 045° 2°W 225° 2°E 045° 2°W 225° 2°E 090° 2°W 270° 1°E 090° 2°W 270° 1°E

135° 1°W 315° 1°E 135° 1°W 315° 1°E

Ref: WN Ch 28 – Measuring Compass Deviation using GPS


Slide 16

Correcting True to Compass

TTruerue

VVariationariation

MMagneticagnetic

DDeviationeviation

CCompassompass

WW EEadd Westgoing down

or.. subtract East

add Eastgoing up

Slide 17

Remembering the Correction

remember…

When converting from True to Compass

• “West is Best” – add West

• “East is Least” – subtract East

Slide 18

Practical Compass Use

Typical Compass• 5° - graduated increments• Read to about 2-3°

Properly corrected compass• Residual Deviation typically < 2°• Ignore Deviation for moderate runs

Slide 19

Fluxgate Compass

Economical Electronic Compass

Uses electronics to sense the magnetic field

Self-compensating• automatically builds deviation table• automatically applies deviation to reading• continuously updates deviation table

Extremely Accurate• Typically < 1°


Slide 20

Fluxgate Compass

Slide 21

Plotting Magnetic

4 x 15 Plotter uses Grid Lines• Oriented to True not Magnetic• Requires conversion

Alternative• Use Compass Rose• Inner scale is oriented to Magnetic• Parallel rules


Slide 22

Compass Rose

Slide 23

SKILL – Using the Compass Rose

Chart Compass Rose provides• Variation• Scale calibrated to Magnetic

Can be used to plot courses

SKILL• Plot & label courses & bearings using

the compass rose


Slide 24

Parallel Rules


Slide 25

Parallel Rules with the Compass Rose

read magneticBearing directly


Slide 26

Using a Rolling Parallel Rule

read magneticBearing directly

Slide 27

Exercise 4-1 - Using Compass Rose

Use Bowditch Bay Chart

Follow instructions in Student Guide• Measure magnetic courses using the

Compass Rose

Slide 28

Exercise 4-1

Plotting with rectangular course plotter and parallel rules using the Compass Rose.

Plot a course from G “7” Fl G 4s Main Channel to G “5” Fl G 4s GONG Main Channel. Measure and label the magnetic course using parallel rules and the nearest compass rose.

C 081M

T = 066V = 015WM = 081

Slide 29

Exercise 4-1



Plot a course from R “6” Fl R 4s Main Channel to R “8” I Q R Main Channel using the rectangular course plotter and the nearest compass rose.

C 081M

T = 066V = 015WM = 081

T = 267V = 015WM = 282

THE OUTER SCALE IS READ FROM A

MERIDIAN OF LONGITUDE. THE

INNER SCALE FROM A PARALLEL

OF LATITUDE.

090

270

180

000

080 070060

050

040

030020

01000

0

260 250240

230

220210

209190

180

100

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280290

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170 160 150140

130

350 340 330 320

310

190200

210

220

230

010020

030

040

050

C 282M

Slide 30

T = 267V = 015WM = 282

Exercise 4-1




Plot and label a course of 220º magnetic from R “4” Fl R 6s BELL Main Channel using the rectangular course plotter and the nearest compass rose.

C 081M

C 282M

M = 220V = 015WT = 205

THE

OU

TER

SC

ALE

IS R

EA

D F

RO

M A

ME

RID

IAN

OF

LON

GIT

UD

E. T

HE

INN

ER

SC

ALE

FR

OM

A P

AR

ALL

EL

OF

LATI

TUD

E.

090

270

180

000

080

070

060050

040 030 020 010000

260

250

240230

220 210 209 190180

100

110

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150140

130

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190

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230

010

020

030

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050

C 2

20M

Slide 31

M = 220V = 015WT = 205

Exercise 4-1




Plot and label a course of 220º magnetic from R “4” Fl R 6s BELL Main Channel using the rectangular course plotter and the nearest compass rose.

Plot and label a course of 029º magnetic from G C “1” Perkins Cove using parallel rules and the nearest compass rose.

C 081M

C 282M

C 2

20M

M = 029V = 015WT = 014

C 0

29M

Slide 32

Cruise

Begin – Part I of Cruise

• Cruise is in 5 parts

• One part with each of remaining sessions

Slide 33

Questions ? … Comments

Documents

Piloting Course Chapter 4 On-the-Water United States Power Squadrons ®