For years, we have used charts, an onboard compass and even some guesswork to find the way to our destination.

The charts are true north and the compasses are magnetic north. Unfortunately all compasses don't agree as to the direction of magnetic north.

Nearby metal objects or electrical current alter the effect of the earth's magnetic field on the compasses internal magnets and cause it to deviate from magnetic north.

To minimize the effect, mount the compass far away from potential problems, like the engine, and never use iron fasteners or fittings nearby. No matter how careful you are, some deviation (five degrees plus or minus) is inevitable. All this makes the compass suspect for many of us.

While the compass is the most important device on your boat, most experts say the best you can expect from a well adjusted one is two degrees, plus or minus. This, added to the pilot's ability to keep the boat within three or five degrees and the compass deviation of up to two degrees, you now have the possibility of seven degrees off course.

A mere two-degree error in bearing from a landmark a mile away can produce a potential 400-foot error. In 10 miles this relates to seven tenths of a mile which can put you in danger or out of site of the waypoint you were looking for.

How do we achieve better accuracy? Very easily. All we need is a Global Positioning System (GPS) onboard. The GPS has revolutionized marine navigation.

A GPS receiver is a marine electronic device that will provide your exact position and help you navigate to your destination.

The 24 satellites orbiting earth will give you an accurate fix on your location on the water anywhere on earth at any time of the day or night and in any kind of weather. It is the most advanced navigation system ever to exist.

This can be an inexpensive hand held GPS costing approximately $100 or a color fixed mounted model priced as high as $2,000, depending on the size of the screens. The best model has chart plotters. Some now come with built in charts of U.S. waters. Some incorporate a sounder (depth finder/fish finder), water temperature, tide charts and much more.

A GPS calculates your present position using a mathematical process called triangulation, which uses intersecting spheres to determine latitude, longitude and altitude.

In order to get three dimensions, the GPS receiver needs to lock into four satellites. The fourth satellite synchronizes time between the satellite's atomic clocks and receiver's quartz clock. It can lead you to a specific position, store a position in memory so you can return at a later time, help you find a favorite fishing or diving spot and get you back home to your dock. It can retrace a route like leaving a breadcrumb trail.

It is accurate to within 40 feet with accuracies of 33 feet or better most of the time. If you have a GPS with Wide Area Augmentation System (WAAS), you can expect position accuracies of 10 feet or better most of the time.

You will never get a busy signal. GPS receivers only listen to satellite transmissions but do not interact.

Once you master all of the features and use it as the chief form of navigation, you will wonder how you got along without a GPS on board. The GPS plotters can be connected to a computer so you can do all your pre-planning and download it into your GPS plotter and also you can buy chips to insert into your GPS plotter for any area in the world. Smart sailors have been using GPS and electronic charting for years to navigate with greater accuracy and peace of mind.

Many captains keep a backup GPS on board just in case the main unit malfunctions. A GPS allows you to preplan your routes, plan and organize routes with your mouse, man overboard functions, view exact real time position on charts, view track logs to sail back the same route, mark good routes, name routes and waypoints for reference and much more.

To learn more about safe boating, take a Boat Smart or Chart Smart course offered by the Cape Coral Power Squadron. The squadron is open from 9 a.m. to noon Monday through Saturday and is at 917 S.E. 47th Terrace.

For more details, call 549-9754.

Wayne and Joan Church are Cape Coral Power Squadron members.