this is a mercusier 140 we had it hooked up to the water hose and it will go in forward gear and reverse but once its in the water all we got is reverse. The guy at the marina that we took it to said it was the shift cable so he fixed it got it on the water it worked for like an hour. the next time we took the boat out it was back to square one all we had was reverse again the guy is telling us it is a dead mans clutch im not sure what that means could someone help us we would like to fix the problem ourselves.