[dplidr@gmail.com]

When I picked up my C&C33 I had a similar problem with bad vibration in forward and none in reverse. Turned out to be a combination of out of alignment engine and non-square coupling on the end of the shaft.

In reverse the rearward force pulls the shaft slightly back, straightening the shaft; while in fwd the force from the propeller amplifies any off-center or out-of-square end wobble. It was bad enough to make the shaft bang against the stub tube. (PO had upsized the shaft from 7/8 to 1-inch without upsizing the rest of the system)

long-short: re-centered based on the skeg and rebuilt stub-tube, re-did the coupling, re-aligned the engine, and replaced the cutlass and stuffing box and all is smooth as can be in both directions.

Good luck!