Speed Log out by around 3 knots
My Nasa Cruiser speed log is out by around 275%! So when the display shows 2 knots my handheld GPS will show 5! Now I do understand that there is some difference between the speed over water but this is way off! The speed log transducer is of the standard paddle wheel type and fitted through-hull positioned in a correct location and with no obstructions. And whilst there is a calibration facility it is limited to +/- 50%!
Any ideas of what the problem could be?