Speed Measurement using a GPS


There are a few different ways of checking how well your boat is going, you can be timed round a course by stopwatch, or your speed checked with a speed gun. the problem with these methods is that you require a second person to do this whilst you are driving the boat. If you usually test on your own, the best solution is to use a GPS receiver. The one most commonly used by boaters is a Garmin Etrex, it is reasonably small and not too heavy. The Etrex can be set to store the maximum speed obtained on a run, it is best to take an average of about four runs because the Etrex is not 100% accurate. The satellites are trying to record a time/distance measurement on a lake that to them must look about the size of a postage stamp.


Weight with waterproof cover 200 grams


The Etrex is reasonably waterproof but not enough to be used on a boat without some additional protection. The best thing is to use an Aquapac or Aquamate cover. these are 100% waterproof and have the added safeguard that if your Etrex falls off the boat, the air trapped inside the cover will leave it floating on the surface.




The dimensions of the Aquamate are 170mm x 106mm, product code AM13, they can be obtained from fellow boater Andy Payne at GTE services for a special boaters price of 10 + P & P. GTE services website


I fit my Etrex onto the wing of my boat with rubber bands, the weight tends to make a smaller boat run a bit flat on the water so further back would be better, but wherever it is fitted you can still see if any changes you have done have improved the boats performance or made it worse.