What Is A Marine GPS? A Fishing Primer (2024)

A boat's control panel with GPS and other devices

If you own a boat or are thinking about owning one, then you’re probably wondering if you need to kit it out with a marine GPS unit. Or maybe you already have marine GPS systems and want to know how it works and the benefits of it.

I used to go boating without a marine GPS system, and life was hard. I never knew my speed, my location, and I could not easily determine where I was based on the land, it was just a guess. Plus I couldn’t venture out fishing out of sight of land, where the bigger fishes are, so it was also frustrating.

Now, I have seen the light. Or map, I should say. A good GPS system will never let you down and will guide you through even the most remote of waters, provided there’s connectivity of course. But that’s just the tip of the iceberg.

Join me as we take a look at what a marine GPS is, how they work, and how they’ll help you out at sea. 

What is a marine GPS? 

Marine or boat GPS devices are units that consist of a display that uses a global positioning system (GPS) to show you your exact location or your exact position on the sea. 

Captain's view of a boat
A Captain’s eye view of the boat

Marine GPS units are the exact same as the units you would use in your car except these are waterproof and made for the sea. On the boat’s GPS display you’ll be able to see your location and follow your position as you move around the ocean, just like driving around a car with a GPS unit. 

How does a marine GPS unit work?

Inside marine GPS units is GPS technology in the form of a GPS receiver or a few GPS receivers. 

To calculate your position and provide marine navigation, all marine GPS devices need to connect to their global positioning system (GPS system) in the form of their GPS satellites via the GPS receivers in the unit. 

The GPS receiver has to be connected to a minimum of 4 satellites within the GPS systems to provide you with an exact location. The GPS device knows the positions of the satellites and uses this GPS data from the GPS receiver to triangulate your exact position. 


Once it’s locked onto the multiple satellites, the GPS unit doesn’t drop the connection, it holds it so you can see where you are, where you have been, and where you are going. 

What is the difference between a GPS and a chart plotter?

GPS units can exist without chart plotters but chart plotters don’t exist without GPS units. Besides that, it’s important to know the functional differences between the two.

A GPS system simply provides you with your location (past, present, and future) and shows you this on a very basic map with hardly any detail on the screen.

Chart plotters have charts (maps) of any areas of the ocean in the world installed which boaters can see on the display (you can pick which charts you want). Boaters then use it in conjunction with GPS to create a GPS chartplotter. 

Close up of a chart plotter
Close up of a Raymarine chart plotter

This gives you the best performance on the water as you can see your position and the mapping data layered on top of each other. So you can not only determine your location but also everything you’re driving over such as reefs, anchorages, depths, and other bits of data too.

Do I need a GPS for my boat?

You don’t need a GPS system on your boat, experienced mariners have been sailing around the world without them for centuries. Is it a good idea to have one on your boat? Yes, and I’ll put it like this.

Vessels that operate with marine electronics systems and equipment like a GPS have far fewer accidents when boating. The vessels always know their position, where they are going, where they have been, and always have the power to navigate to safety when needs be. 

Without a GPS system, many boaters without the knowledge of how to do things manually like dead reckoning with charts and a compass, or using a sextant to work out their position, will crash boats into reefs, miss channels to harbors, and generally have an unsafe experience. 

Can you use your phone as a Marine GPS?

Yes, I often use my phone as a marine GPS unit when I’m on a boat without one. 


If you download the Navionics app and buy the charts for your area, you’ll suddenly have a GPS chartplotter system on your phone that shows you everything a normal marine GPS unit would. 

Navionics works for navigation and seeing what the bottom contours are like but it doesn’t have the features of dedicated units. Here’s a video going over it’s features

A quick tutorial on the Navionics app

Why You Need GPS on Your Boat

You can’t just ask “what is a marine GPS?” you also need to ask why you need them. There are loads of reasons why you need a GPS system on your boat. They make life so much safer and easier on the water and here is how. 

Journey Planning 

GPS systems give you all kinds of data features on top of location. They tell you your speed, allow you to set a ‘go to’ (basically a destination), will show you the most direct route to your destination, and your expected arrival time. 

All this boating info allows you to plan your journey based on time, daylight, weather conditions, fuel consumption, and more. Provided there are nearby satellites of course.

Three people reading documents on a boat
Sailors at sea planning their journey

You could set your “go-to” as 60 miles northeast of you at a speed of 8 knots and it spits out a route and arrival time for you. You can then think “Do I have enough fuel for 7.5 hours of cruising?” or “Will I be able to get there before it’s dark?”. 

Saving Place You Want To Return To 

If you’re scuba diving or fishing (I’m always fishing), and you find loads of aquatic life in a certain area, you can hit “mark” on all GPS devices to save that location down to 10 meters of accuracy. 

… you can return to the exact same spot without any guesswork.

This means that next time you want to find your next catch or have a nice dive, you can return to the exact same spot without any guesswork. Plus, if you end up finding fishes in other areas, you can ‘mark’ those waypoints on the system too.

Connecting It To Other Devices 

GPS systems can be hooked up to all sorts of other units such as a depth finders’ sonar, VHF radio, radar units, auto-pilot, and other equipment too. 

Radar uses radio signals to determine where other boats are allowing you to avoid them or seek help when on the water, and radar is especially useful when boating at night. 

A VHF with a GPS connection allows for digital selective calling outside of emergency bands, and when in an emergency the VHF can broadcast your exact latitude and longitude to rescuers for a quick evacuation. 

Control panel of a larger boat with screens and joysticks
Larger boats will have more devices in their cockpit

When a GPS is used with depth finders, you can see your location and an image of what’s underwater at the same time, making it easy to find areas with lots of potential catch and target them with ease.

With an auto-pilot connected, you can plug in a coordinate into the GPS, connect to satellites, set the speed, and the boat will drive itself there for you. Life couldn’t be easier. 

Other Uses for GPS on Boats

Anchor Alarm

Users also like GPS’ for the anchor alarm. If your boat’s anchor slips at night, an alarm is sounded waking up the crew and captain so that they can re-anchor the boat and not drift aimlessly through the night. 

Security System

GPS’ can also be used as a security system. If your boat gets stolen, the GPS can ping you its position so the authorities can find it again, and even set off an alarm if it goes out of the range you have specified, so you can apprehend the thieves. 

Additional Features To Think About 

GPS Size and Display

GPS’s come in many shapes and sizes from portable units which fit in your pocket to large ones for ships. One key thing to think about is display size or screen size. The bigger the screen the easier it’s going to be to see all the data that is on it. 

But, larger screens often cost more so it’s worth playing the balance. On a boat, you don’t want a small screen as you’ll be squinting to see the details, something around 7 inches or larger is ideal. 


Some marine GPS systems that have a fishfinder built-in can actually draw maps of the underwater features you drive over. This allows you to build the most detailed map of your fishing or diving spots with waypoints available and it actually saves this data which you can then download on your computer for analysis. 

Fish finder mounted on a boat's dashboard
Fish finder mounted to a boat’s dashboard

Other users also share their data, so between you all, you can build a fully up-to-date map of the areas you spend your time on. 

Wireless Connectivity

One of the best features new GPS units come with is built-in Wifi or Bluetooth. With this kind of feature, you can see the screen on your phone from anywhere on the boat and even do things beyond connecting to satellites like remote control the autopilot or your trolling motor from your phone too.

Navigating Out 

Thanks for reading my article. I hope you enjoyed it and now know the answer to the question “What is a marine GPS?”, what a marine GPS can do and why they are extremely useful to have on boats. They take away the guesswork and make life on the water safer, easier, and more productive.

Please share the article with anyone who might benefit from it and check out my other articles like best handheld fishing gps units review or best headlamp for fishing review.

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