Launched my pontoon boat today, noticed my 15 hp 4 stroke mercury (2003) didn't move in reverse. I tried forward and it worked fine. spent about an hour on the water and went back to the dock. I again tried to use reverse, but no go, then I put it in forward and the boat would not move. I shut down the motor and put it in forward, tried to spin the prop and it spun freely, same in reverse.