Finding your way on the water doesn’t have to be intimidating, thanks to developments in electronic navigation technology.
GPS: Theory of Operation
A Global Positioning System (GPS) unit receives signals from 24 US Government satellites orbiting at 11,000 miles above the earth. A GPS measures how long it takes these signals to travel from the satellite to the GPS unit, and then multiplies this figure by the speed of light. This simple equation allows the GPS to determine the precise distance between the satellite sending the signal and the GPS receiver.
When your GPS locks on to transmissions from at least three individual satellites, it can calculate your position in two dimensions—latitude and longitude—usually within about 10 yards or less. Locking on to a fourth satellite signal enables a GPS to determine your location in three dimensions: latitude, longitude, and altitude.
The remarkable thing about the Global Positioning System is that the satellite navigational information is available to anyone, anywhere, free of charge. Of course, you’ve got to buy a GPS receiver to use the data, but it’s not a tremendous investment, considering the GPS’s capabilities.
Which One?
A handheld GPS is ideal for small boats, providing accuracy in a compact unit. Battery operated, a handheld GPS requires no permanent mounts thus not using valuable console space in the boat.
Mountable (or portable) GPS receivers have larger display screens, bigger push buttons, and more features than you’ll find on handheld units. Most GPS’s in this category operate on batteries and/or on external 12 volt power.
Portable GPS units come with mounting brackets to hold the GPS in place while underway. When your cruise is over, you can remove the GPS for safekeeping.
Fixed-mount GPS receivers offer the largest displays and most features; fixed mount GPS units are meant to be permanently installed on your boat.
A stand-alone GPS is often referred to as a chartplotter. Many fixed-mount GPS’s combine satellite navigation with fish finding functions into one compact electronic module.

The majority of GPS units have a basic map pre-installed in them, with the capability of adding more maps later as necessary. To expand your GPS’s mapping knowledge base, you can, for a nominal fee, download maps from CD-ROMs—or acquire data cards containing very detailed regional maps for specific areas.


Moving Forward

The fact that we can find our way using satellites is astounding, but the idea of integrating a GPS unit with other on-board electronics seems a bit futuristic—like something out of a science-fiction movie.
We’re pleased to report that the future has arrived, and merging your boat’s electronic devices with a GPS is easier than you might imagine. The technology is now available to network a GPS with radar, sonar, VHF marine radio, and a boat’s autopilot system—just to mention a few of the more “common” networking applications on the market.
The Global Positioning System offers seemingly endless possibilities for the high-tech boater—limited only by how fast the electronics manufacturers can develop new products—and by how much of an investment you’re willing to make in your boat.
GPS is a wonderful invention. However, like any other piece of equipment, a GPS unit isn’t infallible—so don’t neglect learning how to navigate with a compass and a chart—just in case.