Interesting! This may be a dumb question but couldn't they have got their position off the screen and then just used a paper chart for navigating to shelter? From your description I assume they just couldn't get an accurate position, or was it that they knew where they were but did not have any usable charts?
I admit that we don't have a plotter at the moment; we use an ipad with charts, and have a roll of paper charts. For Cat 3 racing we need a "permanently attached" GPS so I was just going to be a cheapass and get a cheap fishing GPS/depthfinder, which has the advantage that you can build a separate battery and mount and put the unit on the dinghy so that it can be used to lead the yacht into dodgy anchorages.