For the model year it most likely is a paddle wheel located in a transducer through hull. They are not very accurate and, if you live in an area where there is a lot of marine growth, it can be impacted by the growth. I now get my speed from a GPS unit tied to a MFD. Apparently, there is a way to remove the transducer while in the water and clean the wheel. I can barely reach my transducer much less pull it out and plug the through hull so am not in a position to do that...