Your Speed Boat Speedometer: How It Works

speedboat speedometerIf you are lucky enough to have a boat, you know the fun and relaxation you can have while skimming the waters. But are you aware of exactly how everything works on your boat? Here is a little information that you might find interesting and helpful.

The Pitometer

The speedometer on a boat is called a pitometer and it measures the speed of the boat as compared to the water speed.

It is different than your car’s speedometer in that way. Cars move over a stationary surface and boats move over water, which is also in motion. Submarines also use a pitometer to measure boat speed. A tube goes through the hull of the boat and into the water. There are two openings in the tube. One measures the water speed as it moves through the tube, and the other measures the water pressure. These two numbers put together give you the exact speed of the boat.

The Impellor Log

The small propellor on your boat is called the impellor log and it, too, measures your boat speed.

The rate of speed of the propellor moves in direct proportion to the water’s speed as it moves by your boat.


The GPS is used nowadays to not only give boaters their exact location, but also to measure boat speed.

One eHow contributor goes on to say, “By using land coordinate information provided by satellites, GPS devices can measure how quickly a boat is traveling based on how much distance it is putting between itself and two or more points.” If your boat’s GPS system is accurate, this is actually the most exact measure of your boat’s speed.

Boating is fun but it can be even more fun when you are aware of how things work. Getting more familiar with how your boat does the wonderful things it does can only enhance your experience on the water.

One Response to “Your Speed Boat Speedometer: How It Works”

  1. Todd Knox

    My boat speedometer and my GPS are close. The boat speedometer registers the same speed as the GPS at speeds below 25 mph and a couple of miles faster than the GPS at speeds above 25. I’m impressed with the boat speedometer in any case.


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