Raymarine ST40 speed slowing
I have a Raymarine ST40 speed wheel indicator that I installed this year. The speed has started to fall off slowly since. According to the GPS I was loosing 1.4 knots last week. I assume that the growth on the hull has interfered with the wheel. I have pulled the boat and cleaned the hull and will clean the wheel. Is there anything I can put on the wheel to help the problem. Boat is in fresh water. Bottom paint is in good condition.