Marine GPS Instructions
The Global Positioning System is operated by the United States Air Force. Originally for military use, it was made available for civilian use in 1983. Since that time, the artificial constellation of GPS satellites has been used to provide geospatial intelligence and navigational capabilities to ships, boats, cars, hunters, fisherman, people afoot, recreational GPS games--such as geocaching--and, of course, military operations. All uses involve moving from one point to another, but marine use involves moving around obstructions and hazards while traveling greater distances than most of the other uses.
-
Plan the Voyage on a Paper Chart
-
Sit down with the most current paper chart, a copy of the latest Notices to Mariners to update the chart's information, and a navigator's blue pencil. If you are sailing outside of the U.S., you should also have a copy of the appropriate Sailing Directions. Mark your starting point, ending point and planned track between them, avoiding land, shallows, wrecks, sandbars and other submerged unpleasantness. Mark and plot the latitude and longitude of each course change, writing the information on the chart at the point where the course change will occur; these points will become way points on your voyage track.
When you have a completed voyage plan on paper, transcribe the way points to a notebook used exclusively for recording way points, together with the reason for the way point. Such an entry might read: "N17.05 W78.20 Pedro Bank SSW of Jamaica, uncharted coral pinnacles." Maintaining this book will allow you to input the way points of a successful voyage track many times, while keeping the GPS memory free.
Set Up the Way Points Needed
-
Follow the directions for your GPS and enter the way points for your voyage, taking them directly from the chart or the book and confirming the latitude and longitude of each way point as you enter it. It may seem unnecessary to recheck the information you just developed, but like the carpenter's saying, "Measure twice and cut once," confirming those way points as they are entered will help ensure a safe voyage.
Maintain a Dead Reckoning Track on the Chart
-
Keep a dead reckoning (DR) track on your chart as your voyage progresses, using the latitude and longitude from your GPS every 30 minutes. Maintaining the DR track while you have GPS available may seem like an exercise in futility, but should your GPS fail for some reason, you will know where you were, what course you were on, and what your speed when the last DR track entry was made. You will know how much time has elapsed and you can plot your probable position using the time-speed-distance formula along your last known heading, allowing you to continue your voyage with minimal inconvenience.
What Your GPS Is Telling You
-
As your boat moves, the GPS will provide you with a variety of information including the course you are steering; your "speed over ground" or "speed of advance," which is the actual speed your vessel is moving across the water; your current latitude and longitude; a visual depiction of the track you are following (not to be confused with the DR track you are keeping on the paper chart); your travel time to the next way point; and how far you are left or right of the most efficient course, so that you may correct your steering. If your GPS is part of a chartplotter, it will also display your relationship to the land masses around you as a moving chart, with your boat at the middle.
Whatever type of GPS you use, always remember that you, as a prudent mariner, are responsible for the safe conduct of a voyage. If the GPS tells you to follow a course that has you standing into danger, ignore the GPS--not good seamanship.
-
