A Vessel's Position

Knowing exactly where you are is a basic necessity for safe operation of your vessel. You may have to deal with shallow water, overhead power lines or a low bridge. Your "Position" relative to such hazards is essential. There are also times when you may require assistance and need to communicate your exact location to the U.S. Coast Guard or a marine assistance company.

A vessel's "Position" is defined as "the exact location of a vessel, expressed in latitude and longitude." Latitude is a measure of your distance (north or south) from the equator. Longitude is a measure of your distance (west or east) from the Prime Meridian at Greenwich, England. Knowing those coordinates will pinpoint your "Position" on the globe.

There are several ways to determine your position. They vary in their degree of accuracy, and also in the degree of difficulty to determine them. You may ascertain your position by Loran (LOng RAnge Navigation), GPS (Global Positioning System), aids to navigation (buoys, dayboards, etc.) or by visible landmarks. Whatever the method employed, the less familiar that you are with the area, the more important knowing your position becomes.

Your navigation chart is the common denominator that will tie all of that information together. Once you find your position on the chart, you can determine the water depth and your proximity to any local hazards. You can also use your position to calculate the remaining distance on your trip.

So what's the big deal? Everybody has to be somewhere! Who cares where you are? Well, there can be times when the odds of something going wrong are increased. During those times, periodically recording the time and your position is even more critical. Further, it may prove to be invaluable later on.

EXAMPLE 1. You are having a problem with your alternator. It may cause your engine to stop, and your radio and GPS to become inoperable. The thing to do in that case is to call the Coast Guard, explain your situation, and request to be put on a "30 minute" communication schedule. Each half-hour you'll report your position. If they don't hear from you at the appointed time, they'll know approximately where you are and can send assistance.

EXAMPLE 2. You are caught in terrible weather. Your visibility is poor. You are navigating by ATON's and landmarks. You can plot the most recent known position on your chart. Using soundings (depths), your recent course, and your speed, you can calculate your approximate position. From that point, you can make an informed decision on your next course.

EXAMPLE 3. You are in a large bay or sound without GPS or Loran. The ATON's are spaced out over great distances. You burned up a lot of fuel due to unexpected rough seas. You may not have enough fuel to get home. If you run out and there are no visible ATON's, you can calculate your approximate position from your last position that was logged.

Your circumstances and the extent to which you expect trouble ahead will guide you in determining how often to record your position. Use your best judgment and you will avoid most disasters. Your passengers are depending on you to get them home safely!

Until next time, I wish you clear skies, fair winds, and calm seas!