
A boat's mph gauge, or speedometer, works by comparing the pressure created by water entering a tube with a static pressure. This is known as positive pressure. The tube can be connected to a plastic piece that mounts to the transom or through a pipe that runs through the lower leg of the motor. Modern boats use GPS signals to calculate speed and are fully electronic.
| Characteristics | Values |
|---|---|
| How it works | Compares the pressure created by water entering the tube with a static pressure |
| Tube style boat mph gauge | Uses a rubber line |
| Modern boats | Speedometer labelled GPS and uses GPS signals to calculate speed |
| Older boats | Mechanical system |
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What You'll Learn
- Boat speedometers can have their pitot tube connected to a plastic piece that mounts to the transom
- Modern boats have the speedometer labelled GPS and they use GPS signals to calculate the speed
- A tube style boat mph gauge uses a rubber line
- Boat speedos work via positive pressure caused by the boat moving forward in the water
- The tube can come off at the back, get pinched or if it comes off the back of the gauge then you will get wet feet very quickly

Boat speedometers can have their pitot tube connected to a plastic piece that mounts to the transom
A boat's mph gauge works via positive pressure. This is caused by the boat moving forward in the water. The pressure created by water entering the tube is compared with a static pressure.
The tube can come off at the back, get pinched, or come off the back of the gauge. This is a problem because it will cause the boat's occupants to get wet feet very quickly. Modern boats have a speedometer labelled GPS and use GPS signals to calculate speed.
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Modern boats have the speedometer labelled GPS and they use GPS signals to calculate the speed
A tube-style boat mph gauge uses a rubber line, which looks like a wire, not a tube. It works via positive pressure caused by the boat moving forward in the water. The pressure created by water entering the tube is compared with a static pressure.
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A tube style boat mph gauge uses a rubber line
The pitot tube of a boat speedometer can be connected to a plastic piece that mounts to the transom or through a pipe that runs through the lower leg of the motor. If the latter is modified, this is the first place to look if the mph gauge is not working.
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Boat speedos work via positive pressure caused by the boat moving forward in the water
The pitot tube of a boat speedometer can be connected to a plastic piece that mounts to the transom or through a pipe that runs through the lower leg of the motor. The tube can come off at the back, get pinched or come off the back of the gauge, which will cause the gauge to stop working. Modern boats have speedometers that use GPS signals to calculate speed.
A tube-style boat mph gauge uses a rubber line that looks like a wire, not a tube.
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The tube can come off at the back, get pinched or if it comes off the back of the gauge then you will get wet feet very quickly
A boat's mph gauge uses a tube style system to measure speed. The tube can come off at the back, get pinched or if it comes off the back of the gauge then you will get wet feet very quickly. This is because the tube is connected to a plastic piece that mounts to the transom or through a pipe that runs through the lower leg of the motor.
The tube is usually made of rubber and looks like a wire. It is not a marine gauge, and if it is not a marine gauge, it probably won't work for very long.
The tube measures the pressure created by water entering it and compares this with a static pressure. This is how the boat's speed is calculated.
Modern boats have a fully electronic system, where the speedometer is labelled GPS and uses GPS signals to calculate the speed.
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Frequently asked questions
A boat speedometer works by measuring the speed of the water passing by the boat. This can be done using GPS or by measuring the pressure of water being forced up a pitot tube.
A pitot tube is a long, thin tube that is open at one end and has a small hole in the other. The open end is placed in the water so that it faces the direction of the water flow. As the boat moves, water is forced up the tube, compressing the air inside and giving a reading on the speedometer.
A car speedometer works by measuring rotation, whereas a boat speedometer does not.
A boat speedometer is called an MPH gauge or a speedometer.











































