I have a Sea Ray 185 with a Mercruiser Engine. New Propeller and New hub. The boat randomly has trouble moving. Boat will move at a very low speed, but when I give it power, the propeller spins, but the boat wont increase speed. Cant figure out why this is happening. Problem is intermittent. Boat worked perfectly for years, but this is a new problem that was not corrected with a replacement prop and hub. Thanks for your help!