Boat Speedometer: The Essentials

Boat speedometers are an essential piece of equipment for any vessel. They help boaters keep track of their speed and stay within the legal limit. There are a few different types of speedos for boats on the market, so it's important to choose the right one for your boat. This article will help you understand the different types of speedometers and what to look for when choosing one for your boat.

What is a Boat Speedometer?

A boat speedometer is a device that measures the speed of a boat. It is usually mounted on the dashboard of the boat. The speedometer measures the speed of the boat in miles per hour or kilometers per hour and can be used to help the captain of the boat to navigate.

The benefits of having a boat speedometer include being able to track your speed, set speed limits, and monitor your engine performance. Speedometers can also be used to find your location and keep track of your progress on a map.

How Does the Speedometer on a Boat Work?

The speedometer on a boat works by measuring the speed of the water passing by the boat. There are four main types of speedometers: pitot tube, paddle wheel, GPS, and electric sensor. To understand these speedo for boats working principles, we’ll discuss the 4 most common types of marine speedometers.

1.     Traditional Boat Speedometer

A traditional boat speedometer uses a pitot tube to measure the speed of the water passing by the boat. The pitot tube is a long, thin tube that is open at one end and has a small hole in the other end. The pitot tube is placed in the water so that the open end is facing the direction of the water flow. As the water flows past the pitot tube, it creates a pressure difference between the inside and outside of the tube. This pressure difference is proportional to the speed of the water.

2.     GPS Speedometer

This marine speedometer works by tracking the position of the boat over time and using GPS to calculate the speed. GPS speedometer for boats can be used to measure the speed of the boat in real-time or to track the speed over time.

3.     Electric Paddle Wheel Speedometer

A boat electric paddle wheel is a device that is used to measure the speed of a boat. It consists of a paddle wheel that is attached to the back of the boat and a sensor that is mounted on the front of the boat. The paddle wheel spins as the boat moves through the water and the sensor measures the speed of the paddle wheel. The speed of the boat is then displayed on a readout.

4.     Electromagnetic Speed Sensor

An electromagnetic speed sensor works by generating an electromagnetic field and measuring the voltage created by a conductor passing through the field.


The sensor is usually mounted on the side of the hull, with the field perpendicular to the direction of travel. As the boat moves through the water, the conductor (usually a metal plate or wire) is forced through the field, and the resulting voltage is used to determine the speed of the boat.

How to Choose the Right Boat Speedometer for your Vessel

There are a few key factors you'll want to keep in mind when choosing the right boat speedometer for your vessel:

Visible display

First, make sure the speedometer you choose has a large, easy-to-read display. Also, choose a display with glare-resistant glass for daylight reading. A backlit display will also come in handy at night.

Water protection

You'll also want to make sure the speedometer is water-resistant or waterproof, in case you get caught in a storm. You don't want your expensive and very useful boat electronic to be ruined by water damage.

Additional readings

Take into account the additional readings the speedometer can provide. Some speedo for boats come with simple displays that show only speed, while others include more advanced features such as RPM, voltage, fuel level, and time. Some speedometers even offer advanced GPS and chart plotting capabilities. Choose the features that best meet your needs.

Intuitive menu

Additionally, consider how easy the speedometer is to use. You don't want to be fumbling with a non-intuitive menu when you're trying to keep an eye on your speed or other measurements. Look for a speedometer with user-friendly menu navigation.

Speed range

Finally, you'll want to make sure the speedometer you choose can measure the full range of speeds your boat is capable of reaching. There's no point in having a speedo for boats that only goes up to 40mph if your boat can reach 60 mph. Choose a speedometer with a wide range of measurements, so you can always be confident in its accuracy.

How to Install a Boat Speedometer

The process for installing a speedo for boats varies depending on its type. have. In this section, we’ll discuss how to install a GPS speedometer for boats since it’s the most common nowadays.

GPS marine speedometer kit:

  • A speedometer with a built-in GPS receiver
  • A mounting bracket
  • Power cables
  • An installation manual
  • Screws and bolts

Other tools needed:

  • A drill
  • A screwdriver
  • Two-12 volts batteries


  1. Choose a location for the speedometer. The speedometer should be mounted in a location that is easily visible to the driver and does not obstruct the view of any gauges or instruments.
  1. Drill a hole in the chosen location large enough to accommodate the speedometer's mounting bracket.
  1. Affix the speedometer's mounting bracket to the chosen location using the screws and bolts provided.
  1. Install the speedometer's wiring harness according to the manufacturer's instructions.
  1. Connect the speedometer to the boat's power supply. You need two 12 V connections, one for the GPS instrument and the other for the backlight.
  1. Connect the speedometer to the boat’s chassis for grounding.
  1. Test the speedometer to ensure proper operation.


Tips on Using a Boat Speedometer

A boat speedometer is a handy tool that allows you to keep track of your speed while out on the water. Here are some tips on how to use a boat speedometer:

  1. Make sure that your speedometer is properly mounted. It should be securely attached to the boat so that it does not move around while you are helming.
  1. Check the speedometer regularly. You should glance at it frequently to make sure that you are staying at a safe speed.
  1. Use the speedometer to help you gauge your speed. If you are unsure of how fast you are going, look at the speedometer to get an idea.
  1. Slow down if necessary. If you are going too fast, you can use the speedometer to help you slow down. 
  1. Be aware of your surroundings. Even if you are following the speed limit, be aware of other boats and obstacles in the water. This will help you avoid accidents.


Are boat speedometers accurate?

Traditional boat speedometers that leverage a pitot tube or paddle wheel are not accurate, as they are affected by moving currents. They only give you an estimate of your boat speed.

Boat digital speedometers are more accurate, as they are not affected by moving currents. However, both types of speedometers can be affected by factors such as wind and the hull of the boat itself.

Do GPS speedometers work everywhere?

Yes, GPS speedometer for boats works everywhere. However, there are some areas where satellite coverage is not as strong, and your speed may not be tracked as accurately.

What is the speedometer on a sailboat called?

The speedometer on a sailboat is called a pitometer log. A log works by measuring the amount of time it takes for the boat to travel a certain distance. This information is then used to calculate the speed of the boat.

Pitometer logs were first used in the late 19th century and were the most common type of speedo for boats until the mid-20th century. Today, they are still used on some sailboats, but GPS systems have largely replaced them.

Is there an app to measure boat speed?

Yes, there are multiple apps that measure boat speed. Some popular options include GPS Speedometer and Odometer for iOS and BoatSpeed or SpeedBot for Android. Each boat digital speedometer app has its own unique set of features, so be sure to read the descriptions carefully to find the one that best suits your needs.


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