Electronic NavigationChapter 23

Many Toys

• Speed up and make easier many tasks• Tools are better with knowledge• Common:

– VHF– Depth Sounder– RADAR– LORAN– GPS– EPIRPBS

Depth Sounders

• Echo sounders

– Time from sound emission and receiving its echo

– Rate sound travels through water is known

• Transmitter-receiver (near helm)

– processes and displays results

• Transducer (on hull)

– Sends ultrasonic pulse and picks up signal

RADAR

• Radio Detection and Ranging

• Transmits microwave which bounces off metal

• Determines distance to and direction of object

• Useful at night and poor visibility

• Not shielded – stay out of beam

RADAR

• 5 parts:– Transmitter: produces radio waves– Modulator: sends waves in pulses– Rotating antenna– Receiver: picks up weak incoming signal

and processes it– Display unit

RADAR

• Pro’s– One object fix (RB and distance)

– Greater distances to objects than visual

– Magnetic anomalies

• Con’s– Training and experience for proper interpretation

– Two people needed

– No small boats if near other objects or shore

– Subject to mechanical or electric failure

Radar Reflectors

• 3 flat, metallic plates set at right angles to each other

• Enhance the strength of transmitted RADAR beam

• Big ships can better see smaller vessels and non-metallic objects

• Used on some buoys and other aids to navigation

RADAR Beacon

• Transmits a coded signal when it detects a RADAR beacon (stronger signal)

• “Racon” or “Raymark” on charts

Land-Based Radio Navigation

• Land-based radio transmitter and shipboard receiver

• Measure time differential between arrival of signals from 2 different stations (master and secondary)

• Charts printed with a lattice of lines (each line same time difference)

LORAN

• Long Range Navigation

• LORAN-C current version

• Covers all navigable waters of North America – See Canadian Aids to Navigation booklet for map

How LORAN-C Works

• Receiver measures time difference between 2 stations (LOP)

• Using 2 sets of MASTER/secondary pairs gives a FIX (microprocessor gives the Lat/Long)

• Problems:– Traveling over a lot of land distorts data– Grids not on large-scale charts

• LORAN’s with microprocessors can store waypoints and calculate:

– Speed over Ground– Velocities of Currents– ETA’s– Cross Track Error

• Some can interface with autopilots and maintain anchor watch

LORAN Capabilities

LORAN Selection Criteria

• Portable?

• Interfacing capabilities

• Antenna installation

• Wiring, grounding, interfacing technicalities

• Daylight readability

• Accuracy

GPS

• Global Positioning System• 24+ polar-orbiting satellites emit position

and time signals in a network covering all earth

• Receiver interprets and displays position (FIX)

• Also displays:– Course over Ground, Speed over Ground

EPIRB

• Emergency Position Indication Radio Beacon• Safety Equipment at Sea• Needs activating when in distress and sinking• Signal picked up by 1 of 4 orbiting satellites • Transmitted to nearest Search and Rescue • Must register with Coast Guard upon purchase