Originally Posted by codprawn
You could of course get a knotted piece of string and a log and time how fast the knots pass through your hand!!!
Cod - you've just reminded me what I did when I got my boat and wanted to see how fast it went. I had an anaemometer (sort of thing sailors use) and on a flat calm day used it to measure "air speed". Having now gone GPS I would say it was pretty accurate!