Lots of suggestions above, but I'm not sure if this has come up: simple test is to start engine
, put in gear
while tied to dock
, observe the shaft area. Check to see that the shaft (and the zinc collar attached to it) are turning at the same rate as the engine
coupling flange. A pair of reference marks, one on the flange, one on the zinc will show this easily.
If they turn at the same rate, there is no slippage between coupling and shaft. Then run up the revs a bit and see if the shaft speeds up similarly. If it does, then slippage in the transmission
is ruled out, and the remaining factor is the connection between prop and shaft. You will need to get into the water
to check that... by leaving the transmission
and trying to turn the prop by hand... should not be possible.
I believe that those tests should isolate the problem.