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Frequently Asked Questions



Marine GPS: Take to the Open Waters

Marine GPS navigation requires knowledge above and beyond land navigation. Rocks, shallow water, and wrecks are common obstacles, and since fog often occurs on coastal waters, it's critical to know where you are. Recreational boaters usually stick close to land and this may seem to be a clear advantage, but that is where the majority of hazards are. GPS gives your location, but you need additional information: charts.

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As with any GPS use, a compass and charts should be mandatory. In addtion to the need to know where hazards are, a compass and charts are backups in case of equipment failure.

For marine GPS, you have basically three choices: handheld, chartplotter, or a computer connected to a GPS. They each have their advantages and disadvantages, and I will go into detail below.

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marine GPS video

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Handheld receivers are uaually just as accurate as any other type, so accuracy shouldn't be an issue when deciding which type to choose. The low cost of a handheld is the chief advantage, as some are available for less than $100 US. Another plus is the ability to use it hiking or in the car.

Keep in mind that you, your boat, and your handheld will all be moving, so the small buttons will be difficult to use at times. Most units accept an optional mounting bracket and this would free up an extra, valuable hand.

The location of the GPS needs to be considered, as you need to be able to see the screen easily. Will it be in direct sunlight? If so, choose a model with a screen that can be read in that situation. Screen size can vary a lot from model to model, so consider that you will want to be able to see the screen without discomfort.

Location again comes into play regarding the antenna. GPS does not work well when held close to the body or through metal. Test the area you are thinking about placing the receiver by looking at the signal strength of the satellites. If the signal is not good where you need to put it, an external antenna is an option for some models. Since a GPS receiver runs on batteries, an external power source would be a good idea. Just make sure the model you get can run off of external power.

Garmin makes a line of handheld models for marine use.


GPS chartplotter

Chartplotters are a big improvement over handhelds. They display the GPS information overlaid on the nautical charts. While not a complete replacement for paper charts, the chartplotter will be the primary navigation tool. The screens are larger, there are usually more buttons, and the buttons are larger. They are meant to be mounted to a fixed surface, and they usually have external antennas, so placement is not an issue.

Chartplotters start at about $400 US and screen sizes vary from about 5 - 10 inches. You will pay a little more for a color screen, but the extra cost is worth being able to discern important features. Many chartplotters are integrated, which means that the GPS receiver and the chartplotter are one unit.

If you have a bigger boat and a bigger budget, chartplotters are available that do not have the GPS integrated within. These usually have larger and better screens. By using the chartplotter to display data from other devices such as radar, depth sounder, etc., the extra cost is justified.

Computer Connected to a GPS

You can use a computer with one of three different types of GPS: chartplotter, sensor (external GPS), or standard GPS receiver. Since computer screens, whether they be laptop or desktop, are not made to work in direct sunlight, the computer is usually used below deck or fitted with a shade.

One advantage is the planning and navigating are done on the same unit. You can plot waypoints and routes on the computer and upload them to the GPS. The computer can also be used to keep record of tracks. Another advantage is a computer has more power than a chartplotter alone, so it can do things like run an application for 3D bathymetric display and there are simply more software choices.

There are even laptops and desktop computers made especially for the marine environment. These will cost more, but if you need a computer exposed to the elements, it's definitely worth the investment. With a computer, it is likely that most upgrades can be done with software and not new hardware - that means lower maintenance costs.

Shipwrite Productions - Marine and Technical Consulting and Publications

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