David Cragg If you ever wondered why your GPS wasn't quite accurate read the first para below etc
read the paragraph but It amused me some years ago when my Brother was first mate on a survey vessel that used Barry Docks as its base. I was spending some time with him and we joined another of their ships as it was re-entering harbour with qualified pilot aboard. We were permitted onto the Bridge and my brother started showing me the equipment they used. We came to the Marine GPS and he showed me the plot of our course and when the resolution was zoomed in we appeared to be driving through a concrete caisson by the side of the sea lock we occupied! I pointed this out and he said there wouldn't be any need for him if the Decca was accurate, but that it was handy to blame if they had a bump. Surprisingly at dinner that night he told us about the four hour stint he had to do maintaining position over a Volcanic Plume on the seabed in mid Atlantic to allow scientists to take samples and conduct some experiments. The advantage being that Volcanic Plumes aren't located on a GPS rendered overlaid map. Trevor
