Navigation 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

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?