Is GPS the right tool for all navigation problems?

It is easy to believe that using a GPS (Global Positioning System) receiver on a boat is the answer to all the navigation problems you will encounter. It is true that they are a great aid to navigation but they should not be relied upon entirely.

Some traditional navigators have often felt that the navigation system in use on the vessel should be capable of being dropped in a bucket of Furuno fixed GPS unit.water and still work! And that to rely on electronic equipment is dangerous. Whilst there is still a case for this belief, it is also true that many boats carry more than one GPS receiver, in fact when I run practical courses there may be 5 or 6 sets aboard. The reduction in cost and size made it possible to have a main unit and at least one spare on any yacht. This still leaves the possibility that the whole network would be shut down, and whilst extremely unlikely a prudent navigator will still have a back up plan.

In practice the main danger in using GPS to navigate is normally operator error caused either by a lack of understanding of the limitations or most commonly by the faulty input of information. This means that as will any system used to navigate, there must be a series of checks in place to pick up any errors in the main system, it is here where most errors happen.

Reymarine RC400 handheld GPS.A basic training exercise I use is to start from a buoy and working from below deck, with only the GPS and the compass as navigation tools, the navigator has to find another buoy near by, the aim being to tell the helm to stop the boat when we are close to the second mark. In at least half the exercises the information is incorrectly entered and we arrive at the wrong place (this includes trainee yachtmasters and instructors). A simple check of bearing and distance from the charted positions against the GPS information would pick this error up.

Some research has been done on the number of strandings in small craft in relation to the knowledge of the vessel's position.

Strandings in relations to knowledge of the vessel's position.

What this shows, is that knowing or thinking you know your exact position is no guarantee that you will not run aground. One or the reasons for this is that basic GPS functions do not predict the vessel's future position or indicate the proximity to hazards. Although the number of incidents is generally decreasing, there are still many accidents that occur when the crew think they are in safe water.

The apparently very accurate positions obtained from GPS tend to encourage their use as the only means of navigation, a simple system of cross checks on the vessels current and future position would show up any errors.

When people are uncertain of their position, they behave more cautiously than when they believe they know their position, the result is that they are less likely to run in to something unexpected than those people who are lost but have not means of knowing it!

GPS is an indispensable tool on any vessel but must be treated as an aid to navigation and not the only system, to use it effectively the navigator must learn about the limitations of the equipment and the simple checks that must be performed to ensure the GPS information is not leading you in to danger.

To ignore the benefits of GPS would be like only using a lead line to check the depth of the water instead of an echo sounder; I am sure that when echo sounders first appeared for yachts that there were similar discussions about their use.


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