Marine GPS

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Garmin GPSMap  Lowrance Raymarine

Marine GPS devices are ushering in a whole new era of boating. Whether you’re an experienced boater or a novice, you can benefit from the accurate guidance a GPS can give you when you’re on the water. Marine GPS devices use the power of Global Positioning Satellites to calculate your exact position in real time and superimpose your course over detailed marine charts. The most sophisticated GPS devices can get you to where you’re going, warn you away from underwater obstructions, find a school of fish, and even alert you when your boat is approaching shallow water.

One of the best attributes of a marine GPS is that it lets you carry less gear when you’re out enjoying the water. With the accuracy of your GPS, you’ll be able to leave the compass and charts stowed away and take care of all your navigation needs with one portable unit. As you might expect, there are many different models of GPS devices on the market, made by many of the most famous names in satellite navigation like Garmin and Lowrance. We’ve put together this handy guide to remind you of all the things you should consider when you’re shopping for a GPS.

How Big Is The Screen?

Screen size is a double-edged sword on land. That’s mostly because dashboard and windshield space is at a premium inside an automobile, and the close proximity of the navigation unit to the driver makes even a small screen readable. There’s usually more elbow room on a boat to mount a GPS unit, and a bigger screen is almost always better and easier to read.

GPS screens can often display all sorts of different types of important information, and boaters have to be aware of many more things over a wider area than a car traveling in defined lanes, so the bigger the better. Of course bigger screens also mean bigger price tags, so your budget might be the overriding factor when you’re choosing your marine GPS by screen size.

How Portable Is It?

Marine GPS units are available as handheld (Magellan eXplorist 510 marine) or larger units that need to be mounted on your vessel (RaymarineGarmin GPSMap, Humminbird, Furuno or Lowrance Elite), either temporarily or permanently. If your boat is big enough to have an enclosed, lockable cabin, you might choose to get a dedicated marine GPS, or a marine GPS with built-in sonar. If your boat’s not much more than a skiff, you might want to keep your GPS in your pocket and only refer to it when you’re underway.

For most boats, you’ll probably want to have some form of mounting bracket that allows you to bring the GPS unit along with you and mount it securely before hauling anchor. You’ll still be able to take it with you when you leave the boat, like a handheld. Boats are notoriously unkind to electronic gear that’s left out in the elements, and it’s an unfortunate fact of life that expensive items like a marine GPS can’t be left out where people can get at them if you want to find them when you return.

How Many Satellites Can The Marine GPS Get A Fix On?

The Global Positioning Satellite system is a group of 31 satellites in medium-earth orbit that allow GPS equipped devices to calculate where you are on the globe by measuring the time it takes for a signal to travel from a satellite to the marine GPS to determine how far away from the satellite you are at any given time. Your GPS unit calculates your exact position by using four or more satellites at the same time to determine the intersecting point of all the signals.

Because of the speed at which these signal travels is so fast, it’s of paramount importance that your marine GPS reads them as many time a second as possible, because an error of only a millisecond can put you off course by hundreds of yard. This measurement of is measured in Hz, for hertz, or times per second, so a bigger number will mean a more accurate reading. Some units can read your position at 10Hz; a common handheld speed is 1 Hz. If you’re counting on pinpoint accuracy from your GPS device, look carefully at this measurement.

How Good Is Your Marine GPS At Connecting To A Computer?

Like their counterparts from land-based activities, some marine GPS devices allow you to hook up to a computer interface and save information like routes you’ve traveled, waypoints you’ve hit, or to load other maps. Some marine GPS units don’t have any outboard capabilities, others have a lot. Most use standard USB ports to communicate with computers as needed; a few have Wifi that make it unnecessary to have any physical connection at all to send and receive data. Many take removable data cards as well.

How Does The Marine GPS Send And Receive Signals?

Most marine GPS units of Furuno, Raymarine, Humminbird, Garmin and Lowrance have internal antennas. Boats are rough and tumble environments, and GPS designers try to avoid anything that protrudes from the side of the units wherever possible. Internal antennas might be less likely to get broken, but they’re also less accurate than an external antenna. If you’re interested in the highest accuracy possible, look for models with external antennas, or models that have a port that allows an external antenna to be added later. If your GPS device is equipped to receive other signals like radio, you’ll be glad you have an external antenna as well.

Additional Safety Features

Raymarine e127 Marine GPS chart plotter fish finder

Raymarine e127 Marine GPS and fish finder

If you’ve ever been out on open water without a marine GPS, you know how much safety and peace of mind your device can give you. Having a GPS on board is one of the basic navigational aids nowadays. Simply charting your position is a great feature, especially at night or in limited visibility, but your GPS should probably be able to perform many more safety functions for you.

Other Signals

Many marine GPS units can receive other signals besides satellite information. Some can receive and send radio signals, handy in case of an emergency.


If you’re worried about collisions when you’re on the water, look for units that sound an audible alarm when you’re too close to any object, including submerged objects. It’s easy to be distracted on a boat, and an audible collision alarm could save your boat, or even your life.

Overboard Alarm

Some units allow you to hit a man overboard alarm that marks the spot on the map where a boater fell overboard. That’s useful to both you and for others to help in the search. It can be especially useful if you’re boating at night.

Waypoint Navigation

If you’re trying to find your way through a tight channel or another tricky course, some marine GPS devices allow you to make a map with waypoints and course directions on it, and recall them as necessary. This capability can be useful on the same day the map is generated if you’re returning to port at night after a day out.

Low Battery Alarm

Some GPS devices are meant to be hard-mounted and run off available 12-volt power onboard; some have rechargeable batteries; and others run off removable batteries. A good marine GPS should sound an alarm when your batteries are running down so you can replace them or return to port in safety before your GPS goes dark.

Voice Activation

If you’ve got one hand on the wheel or tiller, and one on the throttle, it can be inconvenient to have to operate your marine GPS using buttons or a touchscreen. Higher quality GPS units can respond to voice commands. If you’re often alone at the wheel, they’re invaluable.

Water Resistance

As any boater can tell you, water resistance is a relative term. Here’s one attribute of a marine GPS that you’ll have to evaluate carefully. Every model will tout their water resistance, so you should refer to reviews by persons that have bought and used the devices to see if the GPS you’re thinking of buying will stand up to the water it’s likely to see.


Marine GPS screens can be grayscale or full color, and they display many different kinds of information. Very basic units don’t show any geographic detail at all, and simply act as a compass and position finder that requires you to look up your location on a chart that shows longitude and latitude. That’s better than no GPS at all, but most users prefer at least a base mapping models that shows the land, the sea, your routes, and waypoints. If you need more detail, higher end models can also have sonar capabilities and can include 3-D views, underwater views, show fish locations, and even weather patterns.

Everything on a boat is usually designed to be compact, and if possible, perform more than one task. You can find GPS units that have expanded capabilities like picking up radio stations to receive weather reports or listen to music, download books that can be read when you’re berthed, or you can even have audio books that can be read aloud to you as you cruise along.