Hull Speed Transducer

[gmerrill]

First of all let me say this is the first sailboat that I've had a speed transducer.  Anyway after being left in the saltwater. Some barnacles grew on the wheel. It wasn't reading at all. I cleaned the wheel off completely. Now it's reading good but it's about 1.5 knots off of my gps. What am I missing. Oh by the way the is a 2018 model.
Greg

[kahpho]

GPS would be speed over the ground while the transducer would be speed through the water. Could you be seeing some current influence?

[gmerrill]

I forgot to mention the speed transducer reading is less than the GPS reading. And yes there is current influence for and against