Navigation NAU 102 Lesson 19

GPS Compass

Piloting Instruments Tools to measure: Direction Distance Speed Depth

Direction Bearing Circle Placed on top of gyro repeater or magnetic compass. Used to measure bearings of terrestrial objects. 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.

A bearing circle with a telescope attached. 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. Set to ship’s heading then bearing is taken. Heading set to 0 = relative bearings Actual heading set = true bearings

Handheld magnetic compass. Configured for ease of taking bearings. Direction Hand Bearing Compass Handheld magnetic compass. Used on small vessels. Configured for ease of taking bearings.

Direction Taking a bearing

return is converted into a physical range. Distance Radar A radio wave is transmitted and returns as an echo. Time interval between transmission and return is converted into a physical range.

Similar to a sextant, but without the shade glass. Distance Stadimeter Similar to a sextant, but without the shade glass.

Distance Stadimeter Measures angles between objects. If separation or height is known, distance can be calculated.

Distance Distance = height of object / tan (angle)

Distance = height of object / tan (angle) The air draft of a vessel is 130 feet. The angle between the top of the mast and the waterline is 8.5° as measured by stadimeter. What is your distance from the ship? Distance = height of object / tan (angle) Distance = 130 ft / tan (8.5°) Distance = 869.9 ft

Speed We can measure: Speed Over Ground (SOG) Speed relative to the fixed earth. Speed Through Water Relative to the water around the vessel.

Speed Chip Log Wood attached to a knotted line. Thrown behind the vessel. Knots counted for a set time period. Speed through the water

Speed Pitot-static Log Retractable “Pit Sword” hangs below vessel. Measures speed by pressure differential. Greater pressure = greater speed

Speed Impeller Log A propeller-type device hangs below the vessel on a rod. Water flow over propeller causes it to spin. Faster spin = faster speed.

Speed Electromagnetic Log Water conducts electricity. Measures induced voltage. Greater voltage = greater water flow.

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.

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?