For all of you boat owners and enthusiasts out there, many, if not most of you would want to know how fast you’re going over water, maybe for the peace of mind the extra information provides, or to legally stay under the speed limit, it goes without saying that you’re going to need the best boat speedometer.
Unlike a ship log, which is the larger version of a boat speedometer used by large ships out in the open sea and measures speed in knots, we will be tackling smaller user-friendly and highly accurate types of speedometers for your next marine adventure.
Now that you want not just any boat speedometer, but the best one, with the plethora of choices out there, how are you supposed to pick the right one?
How Does a Boat Speedometer Work?
Well, you have to know how it works, but before we head deep down into the nitty-gritty inner workings of a boat speedometer, first we'll look at the types of boat speedometers out there, what makes them special, why you would pick one over the other, and what would be the best boat speedometer for you.
GPS vs Manual
Boat speedometers work by measuring the speed of the boat you're on and displaying it on a panel. Simple enough, not to mention a fancy-sounding Global Positioning System (which is what GPS stands for by the way) compared to a manual boat speedometer would be a no-brainer, right? Well, not exactly, and here's why.
GPS speedometers are a more modern way of reading your boat speed and work just like the ones on your smartphone or your car. These GPS speedometers tend to be easy to install as they only require connections to power and their antenna/s.
The downside to GPS speedometers is that they are primarily affected by weather conditions, as they require good weather and have ample signal reception to operate optimally due to the wireless connection with the satellites. Accuracy may drop significantly depending on the severity of bad weather.
With this in mind, these types of speedometers also have something called a refresh rate, which is the time it takes for your current speed to update. Some have slower refresh rates and some have higher and could be a determining factor for you when shopping for one.
Some models are even capable of showing you your COG (course over ground). This helps with navigation and is conveniently placed on the speedometer itself for easy referencing.
With regards to installation, GPS speedometers require either a single antenna or multiple antennas depending on the model. Another thing to note about GPS speedometers is that they come in two flavors, and is a matter of preference.
Digital GPS Speedometer
Digital GPS speedometers display your speed as a number you can straight up read. If your speedometer supports it, sometimes it can also display direction, mileage, range, and may also come with an odometer included. You would prefer this if you like the extra information being constantly displayed.
Analog GPS Speedometer
Analog GPS speedometers display your speed on a gauge that you have to read first, like the speedometers on your car. They also come with an odometer included. This type of GPS speedometer is a more compact version where only the necessary information is displayed and it has the unique aesthetic only an analog display can provide.
Manual speedometers work by using what's called a pitot tube which is essentially a small tube with a hole, that goes through your boat's hull and down into the water. As you move along the water's surface, the pitot tube fills up with water, pressurizing the air trapped inside. This air pressure is then measured by the manual speedometer, the higher the air pressure, the faster the speed, the lower the air pressure, the slower the speed.
Due to being mechanical in nature, manual speedometers tend to be slightly more inconvenient to install than GPS speedometers, but refresh rates are not present in these kinds of speedometers since the speed reading is updated instantaneously.
However, manual boat speedometers will work no matter the weather conditions - as long as the water is moving, your speed will be displayed. Tides and passing waves can make it seem like your boat is moving regardless of the boat's actual position.
Things to Look for and Consider when Buying a Boat Speedometer
Most speedometers nowadays have a ton of shiny features and that can sometimes blind the uninitiated to what is truly essential in one.
Accuracy and Navigation
First of all, you have to make sure that whatever you're buying is accurate. All of the ones listed here have been thoroughly researched and come from brands with well-known reputations and as such are the most accurate out there.
In terms of navigation, some speedometers come with a COG display which may or may not be to your liking, but we've made sure to mention the feature on those with one so you don't have to worry about missing out.
Imperial or Metric
Oh, and knots too. Pretty self-explanatory, some prefer km/h some mi/h, or maybe knots, and we've got that covered in our top choices.
Ease of Installation
In general, GPS speedometers take the win on this one, as they only require a connection to some power, and sometimes, the installation of external antennas. Manual speedometers, on the other hand, need to have a pitot tube mounted on the hull of your boat and require some tubing straight to the speedometer, but hey most of them don't need any electricity.
Control Panel Readability and Water/Dust Resistance
What's the first thing you see when looking at a speedometer? The transparent cover. It may be made of a flat cover or a curved glass dome, so that's up to your preference. Different brands also have different layouts and colors so keep that in mind especially when you're going to end up frequently looking at the speedometer for the foreseeable future.
Water and dust resistance is a must-have, though you don't necessarily need it to be waterproof, there is some assurance in being able to handle some splashes and the overall humid environment.
The Best Boat Speedometer Choices
Not all speedometers are the same, and there are many things to consider when choosing one. Not everyone has the time for that so we’ve compiled a list of the best boat speedometers you can buy for your boat.
True to its name, this is a digital GPS speedometer with a multitude of features. Its smart-looking yet compact waterproof design also some amount of impact resistance compliant to IP65 standard ratings.
This GPS boat speedometer can measure up to a value of 300 numerically and you have the option to change the unit of measurement to knots, mph, or km/h with the press of a button. It is fairly fast especially with its 0.25-second refresh rate.
In terms of display, this GPS boat speedometer has a modern design and ample readability even under direct sunlight due to its flat glass cover and bright display, and its backlight helps with readability under low light conditions.
Not only can it display your current speed, but it also includes a trip meter, a compass, a maximum speed recall function, and a resettable odometer. This unit also happens to be the only device on the list with a trip meter and a speed recall system.
The Sierra International Arctic 4 Gauge Outboard Set is a speedometer kit with a manual speedometer plus a set of gauges that includes a tachometer for reading motor rpm, a voltmeter for reading battery voltage, and finally a fuel gauge.
The boat speedometer is as simple as it gets. It operates by using a pitot tube just like any manual speedometer and displays it on an analog gauge, that shows up to 65 miles per hour and 100 kilometers per hour. It is highly accurate and just as reliable as any digital GPS speedometer out there.
The gauges do have a backlight bright enough for nighttime use and the flat glass and clean white gauge background have the simplicity and retro look that only Sierra can give you.
Although it is not necessary to install everything for the speedometer itself to work, the value you get for the entire set is amazing compared to the other listings of boat speedometers.
Here we have another analog GPS boat speedometer. The Faria 33839 Chesapeake White SS GPS, has a nice aesthetic to it with blue and black text over a white background. It displays up to 60mph and 90km/h, has perimeter lighting for low light conditions polished stainless steel bezel, and a domed glass lens.
LCD shows COG with an accuracy within one degree and has a speed-accuracy within one mile an hour, and most importantly, reliable satellite acquisition time that only takes a second from a hot start. With specifications like these, Faria is sure to satisfy your needs.
This speedometer is particularly great when used on boats that travel with more relaxed speeds, since pitot tubes have difficulty in this scenario, and is overall a better option than manual speedometers with pitot tubes that do not have long lifetimes.
Another analog GPS speedometer on our list, with superb GPS compatibility and a high refresh rate. Its gauge displays your current speed of up to 160 and that's in MPH only, and has a digital display for its total mileage but is nonresettable. It has a more familiar aesthetic of white text on a black background, it also has a red backlight for low light conditions. Installation is a breeze, as connecting it to the boat only requires three wires.
Being IP67 waterproof and dustproof, it is simple, reliable, and gets the job done.
A manual speedometer from Faria. The Faria 32810 may not be chock full of features but it offers that which you need and quite accurately at that.
It can display up to 55mph or 90kph on white text overlayed on top of a black background which is unlike the other Faria speedometers on this list. This comes with a backlight as well and the large numbers on the gauge make your current speed easy to read.
It comes from a brand with a solid reputation for a manual speedometer but does keep in mind that speed is all it displays, so no compass or mileage. But for its price, its value is next to none.
The Samdo 85mm GPS Boat speedometer is a bit of an unusual device compared to the others listed here. It is a universal one, which means it can be mounted on an offroad vehicle, a motorcycle, or a boat. You have total control over its installation.
It features up to a 160mph speed reading, displays your total mileage on the LCD and your current speed on an analog gauge with white text and black background and it has a red backlight.
It is IP67 waterproof, dustproof, rainproof, and even has an anti-fogging capability. Although the odometer cannot be reset, it still keeps on recording even without power.
The fact that it is universal means that it is easy to install and will show you your speed as conveniently as possible.
Yet another entry from Faria, showing how accurate and trustworthy this brand is. It has black and blue text over a white background just like other Faria speedometers and displays up to 60mph and 100kph. It has perimeter lighting and is covered up by a domed glass lens.
What is unique about this analog GPS speedometer is that it has a small black text on a green background LCD under the gauge that displays your COG (course over ground) and actual heading (compass heading over ground) which makes navigation that much more convenient.
This is an IP65 waterproof and dustproof digital GPS speedometer from LATNEX, and it has a clean-looking LCD with a green backlight. Although it is universal make no mistake as this is filled with modern features.
With a bright digital display, readability is not an issue under low light conditions or when under sunlight. Speed can be displayed in more than one unit at the push of a button. It can display any speed within the range of 0-999 and allows you to set it to KM/H, MI/H, or NMI/H.
This model comes with a settable alarm system unique to this device. You can set high-speed or low-speed alarms, wherein a red LED will flash when the alarm is triggered. Highly accurate with errors not exceeding +/-1km and a settable 0.5s or 0.2s refresh rate. 24hr time must be user set and uses any voltage between 10-24 volts.
Low power consumption, easy to install, and with wires already included, what more could you ask for.
Yet another offering from Sierra. The International Ecplise 4 is one of the best boat speedometer kits out there. This is a set of manual speedometer, tachometer, fuel, and voltage gauges. Unlike the Sierra International Arctic 4, this model uses blue and white text on a black background and covered with a glass panel.
The speedometer readings range from 0 to 65MPH and 0-100KM/H. The fuel and voltage gauges are measured in quarters and 8-18V, respectively. Lastly, the tachometer can show readings from 0-7000rpm.
As Sierra has a well-known reputation in marine instrumentation, marine engine, and drive parts you can be sure that their readings are as accurate as they can be.
10. Your Smartphone
Now if you've already ordered a speedometer but can't wait for it to arrive, or you're in a hurry to go on that marine adventure trip right now, here's a suggestion. Your very own smartphone.
Any recently built smartphone has the ability to act as a portable boat speedometer, all you need to do is to download a boat speedometer app and it uses the phone's GPS to display your speed, in knots, MPH, or KPH.
In terms of accuracy under ideal conditions, it's just as good as any GPS speedometer out there, but do note that it will have a slower refresh rate. This is due to the lack of external antennas and the low power nature of smartphones, which can cause significant delays in the current speed displayed the farther you are from civilization.
Frequently Asked Questions
Are GPS speedometers any good?
Yes, they are one of the most accurate and reliable speedometers out there, provided that you use them according to the manufacturer's specifications.
How does a GPS speedometer work on a boat?
It works by sending a signal to a satellite out in space, measures the time it takes for that satellite to send a reply, does some really complicated mathematical calculations in a fraction of a second, figures out how fast you're moving from one point to another, and then finally displays it on the speedometer itself, for you to read at your leisure.
What is a ship's speedometer called?
It is a device known as a ship log, which is the larger version of a boat speedometer, and is used by large ships.
What is COG on a speedometer?
COG stands for Course Over Ground which is a technical term that just shows the direction of your movement.
How do you test a boat speedometer?
For manual speedometers, you can take a syringe and squirt some water over the pitot tube device and see if the speed displayed changes accordingly. For GPS speedometers you'd have to move around with it. You can also use your smartphone, to check if you get similar speeds with either the manual or GPS speedometer.
Are boat speedometers accurate?
Absolutely, GPS speedometers, in particular, happen to be more accurate than manual speedometers under ideal conditions.
Regardless of the model or its features what matters is that a speedometer provides you with accurate and reliable readings and is compatible with your boat.
Whether going on a marine adventure or a simple fishing trip now you know how to choose the best boat speedometer for you.