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NAU 102

Lesson 19

New Advances

Flux Gate Magnetic Compass

Ring Laser Gyrocompasss

GPS Compass & DGPS Compass

Flux Gate Compass

Two harmonic coils wrapped around a magnetic core.

Earth’s magnetic field changes the core’s magnetic induction.

The coils sense the changes.

Electronics calculate the magnetic field necessary to cause the change.

Flux Gate Compass

Flux Gate Compass

To minimize deviation, the sensor is placed at the top of the mast.

Residual deviation is automatically calculated as the ship changes course 360°.

It makes its own deviation table!

Deviation is automatically applied.

Flux Gate Compass

Operator can input the variation.

Resulting true direction is sent to digital equipment.

Ring Laser Gyrocompass

Two laser beams travel in opposite directions around a fiber-optic ring.

When the compass (the ship) isn’t turning, the beams are in phase.

When the compass turns, the beams are out of phase.

The quicker the turn, the larger the phase differences.

Ring Laser Gyrocompass

GPS Compass

Piloting Instruments

Tools to measure:

Direction

Distance

Depth

Speed

Direction

Bearing Circle

Placed on top of gyro repeater or magnetic

compass.

Peep vane and far vane (wire) are lined up with

object of interest.

Compass card is reflected by mirror.

Direction

Azimuth Circle

A bearing circle with attachments for

celestial observations.

Azimuth = bearing of a celestial object.

Direction

Telescopic Alidade

A bearing circle with a telescope

attached.

Object is magnified, enabling greater

precision, especially at long range.

Direction

Pelorus

A “dumb compass”

A rotating compass card on a fixed stand.

Heading set to 0 = relative bearings

Actual heading set = true bearings

Set to ship’s heading then bearing is taken.

Direction

Hand Bearing Compass

Handheld magnetic compass.

Configured for ease of taking bearings.

Used on small vessels.

Direction

Taking a bearing

Distance

Radar

A radio wave is transmitted and returns

as an echo. Time interval between transmission and

return is converted into a physical range.

Distance

Stadimeter

Distance

Measures angles between objects.

If separation or height is known, distance can be calculated.

Distance

Distance = height of object / tan (angle)

Speed

Can measure:

Speed Over Ground (SOG)

Speed Through Water

Speed relative to the fixed earth.

Relative to water around the vessel.

Speed

Chip Log

Wood attached to a knotted line.

Knots counted for a set time period.

Thrown behind the vessel

Speed through the water

Speed

Pitot-static Log

Retractable “Pit Sword” hangs below vessel.

Greater pressure = greater speed

Measures speed by pressure differential.

Speed

Impeller Log

A propeller-type device hangs below the vessel on a rod.

Faster spin = faster speed.

Water flow over propeller causes it to spin.

Speed

Electromagnetic Log

Water conducts electricity.

Greater voltage = greater water flow.

Measures induced voltage.

Speed

Doppler Speed Log

Measures frequency shift of reflected sound waves.

SOG or Speed Through Water

Speed

Taffrail Log

Depth

Echo Sounder (Fathometer)

Sound is transmitted and reflected from the bottom.

Depth

Depth = speed x ½ time interval

Speed is set at 4800 ft/sec.

But, it varies with salinity, temperature, pressure.

Depth

Can display depth in feet, fathoms or meters.

Check the setting!

Depth

Piloting Instruments

Dividers/Compass

Piloting Instruments

Triangles

Piloting Instruments

Parallel Rulers

Piloting Instruments

Parallel Plotter

Piloting Instruments

Three Arm Protractor

Piloting Instruments

Nautical Slide Rule

Introduction to Navigation

Questions?