GPS navigation helps boaters find way

The advent of the Global Positioning System (GPS) allows us mortals to become on-water navigators the likes of Columbus or Magellan. However, there are a few things we need to know.

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First, a little background. GPS relies on a system of satellites to pinpoint our position, and it updates that information as we move. Most modern GPS receivers will use up to 12 satellites. Each satellite sends a signal to our receiver. Because each satellite is a different distance from the receiver, the signals take different times to complete their journey. It is this time difference, measured by an atomic clock aboard each satellite, that pinpoints our position.

Thus, our receiver must be able to "see" the satellites. Docking under a tin roof or cruising in a narrow channel with hills around sometimes will block the signal. Because the satellites are south of the area, it helps to point the antenna in that direction.

Now, that is all the GPS does. Even the cheapest receiver on the market will do this and just as accurately as the more expensive units. All the other goodies the GPS provides are built into the receivers. So the more you spend, the more features will be yours.

And what great features they are. Because the GPS receiver updates its position by the second, it will tell you your speed over the ground, the direction you are going and when you will get to your destination. How's that for making it easier to cruise?

The more expensive receivers have built-in charts that will show your boat as an icon moving on the chart. This is very helpful as the GPS has no idea what is in front of you. It will take you directly to your next waypoint -- right over an island if it is there. The moving map helps prevent such mistakes.

But I have used a new term: waypoint. A waypoint is a place on the chart that we know is accurate. It is an electronic place, not necessarily a physical location, such as a buoy. Before a trip, lay out the course on a chart -- a paper one or one in the receiver (if we have spent the bucks to get the moving map kind).

Put a series of waypoints into the receiver. Connecting these waypoints creates the course.

How you enter these waypoints depends on the receiver, but usually they are put in using latitude/longitude coordinates -- or by simply clicking the receiver's mouse on the spot you want the waypoint to be.

The less expensive receivers, without moving maps, will show a highway-like picture between the waypoints you have entered. To navigate, keep your boat icon on the centerline of the highway. When you reach a turn waypoint, make your turn and follow the centerline. If your boat icon drifts to the right of the centerline, steer left until you reconnect with it. Your GPS will show your correct heading, speed, time to the next waypoint and speed made good over the course behind you.

A miracle? Well, close to it, but there are some things to watch out for.

First, the GPS is electronic and will fail if electricity stops. The prudent mariner will have a secondary means of navigation, such as a compass and chart. Then don't forget there may be hard stuff between your waypoints.

Later this fall, the Coast Guard Auxiliary and the Corps of Engineers will offer a GPS for Mariners course. Read this newspaper for dates and times.

John L. VanOsdol is commander of the U.S. Coast Guard Auxiliary, CSRA Flotilla. He can be reached at (864) 391-2170, or at jlvano@wctel.net.