How does a speedometer on a boat work?

Answer 1

A few types exist. One has a little prop which spins in the water flow and electronics convert spin speed to boat speed. Another type uses doppler echo into the water and computes boat speed from result. Another type has a forward pointing tube like an airspeed indicator on a plane and computed boat speed according to pressure in the tube. GPS of course computes your speed over land, not speed over water by your changing position computed from a number of satellites.

Answer 2

Boat Speedometer

Answer 3

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RE:
How does a speedometer on a boat work?

Answer 4

Your "speedometer" does not measure speed made good, but speed through the water. In my view pitot tubes are useless and are unreliable for the exactly the problems you encountered. Get rid of it and use your GPS. Best thing to do is to practice prudent coastal or celestrial navigation.

Answer 5

"The pitot (pronounced pee-toe) static tube system is an ingenious device used by airplanes and boats for measuring forward speed. The device is really a differential pressure gauge and was invented by Henri Pitot in 1732.... The open end of the pitot tube, usually mounted on a wing, faces toward the flow of air or water. The air speed indicator actually measures the difference between a static sensor not in the air stream and a sensor (pitot tube) in the air stream. When the airplane is standing still, the pressure in each tube is equal and the air speed indicator shows zero. The rush of air in flight causes a pressure differential between the static tube and the pitot tube. The pressure differential makes the pointer on the air speed indicator move. An increase in forward speed raises the pressure at the end of the pitot tube. In turn, the air pressure pushes against a flexible diaphragm that moves a connected mechanical pointer on the face of the indicator. The indicator is calibrated to compensate for winds in the air or the speed of the opposing current in the water. In airplanes, electronics also compensate for altitude and air temperature to make the air speed measurement accurate."

Answer 6

on the bottom of my boat is the speedo transponder and it has a little plastic arm on a pin and points down as the boat starts going faster the water Resistance against the arm forces it to swing upward giving a reading to send to the gauge. ive often wondered how accurate this is considering water currants and wind but then again is really necessary to know exactly how fast your going on the water

Answer 7

Not accutate. Any way most are air pressure device at the transom a small fin sticks into the water water pressure pushes air in the tubing and that pressure moves the needle on the dash.

Answer 8

keyed off of water movement over an accumulator or rotato stlye armature wich is calibrated to signal mph or kph