With modern GPS units such a complex measurement area is not needed.

Just set the GPS unit to record location points at some small interval like anywhere from 1 to 10 sec and just blast around for a while strying to get the best speed out of the boat.

Read the track in a PC and look for a 500 mtr stretch where the average speed is highest. This will also negate any negative effects of a windshift etc.

See here an example :





We made this track with a 150 US$ handheld GPS unit (Garmin Geko 201) with intervals set at 10 seconds. However It can log 10,000 points with 1 second intervals = just shy of 3 hours logging at a very high rate. Don't use single points or momentary speed readings they are to undependable. Select a series of points on one track and average the result this is very accurate.

Interesting to note is that in this test the boat achieved the same top speeds on all possible courses. Upwind, downwind and on a reach. The differences were less than 1 km/u = less 1 foot/sec for you imperial guys.

Highest average speed reached over a 10 second stretch was 30 km/u or 16.2 knots.

Wouter