@foxriverat I'm using the GPS Hydrophase on a V6 Mercruiser 4.3mpi, I currently ski at 49kph and use the GPS mode.
The system works quite well, been using it for 9 months now and no problems, it;s very simple to use, all you have to do is turn a knob and the speed will increase/decrease by 0.1 kph/mph.