This past weekend I had the opportunity to participate on a panel discussion at the Maine Fishermen’s Forum. The discussion focused on the use of positioning receivers by fishermen and listening to the other speaker and the audience comments one concept came through very clearly. On the water performance should be defined by the error circle and not the absolute position accuracy.
I am reminded of an incident that occurred last summer. My mother had a 32′ Bristol sailboat that she chartered out. Last summer she came back with a chunk missing out of the port side. Apparently the two sailors had set a buoy as a way point and had been so enthralled with the chart plotter that they drove as if playing a computer game. At the last minute the wife finally looked up and realized that they were about to sail straight into the buoy. After running into the buoy all the two sailors could do was marvel about how accurate GPS was. Personally I think they were simply running on a bad luck streak. Ignoring the absolute accuracy of the GPS unit the swing circle of the buoy they managed to run into was so large that it really was simply bad luck that they ran into it.
As with any incident there are several take aways…not the least of which is that you should watch where you are going when driving a boat.
But when looking at the application of the positioning technology for navigation I argue strongly that it is the potential error rather than the absolute accuracy that matters the most. Having an appreciation for what the position on the chart plotter really means is critical to the safe operation of any vessel. Understanding that just because the chart plotter is showing you in the middle of the channel does not mean you are really in the middle of the channel. In many narrow channels and inlets the potential positioning error can easily place the actual location of the vessel outside of the channel and in harms way.
Unfortunately, many mariners today drive their boats based solely on their chart plotter without ever looking out over the bow. They may have looked on the spec. sheet and seen some claim by the GPS manufacturer about positioning accuracy but you can generally be assured that they did not dig into the details of the claim. The accuracy is taken for granted and people can’t understand when they end up hard up the rocks when their navigational system says they are in good water.
