We recently surveyed/seatrial a Marlow 65C which had a lot of vibration. The port cutlass bearing was worn enough to warrant replacement and the stb trim tab would actuate down but not return up. They were able to get the tab up to run the seatrial (said boat did not need tabs to run) but did not get the message to the Captain and he trim the tabs down. Of course boat was leaning to port during the run after trying to raise the tabs. I was told two different possibilities for the noticeable shaking vibration, that it could be the underwater exhaust at certain rpm's, and with the stb tab down it would make the stabilizers try to compensate for the leaning to port. The surveyor said he could see the stb engine noticeably moving when this was happening. They are hauling the boat and doing repairs to seatrail again. What bothers me is the comments about exhaust vibration at higher rpm's and saying I would not normally be cruising at that speed anyway. No problems at slow cruise. Anyone experienced a similar situation with a tab down affecting stabilizers or with underwater exhaust vibration??