Marlow 65' seatrial vibration

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??

Not trying start a controversy, but I have no experience with stabilizers, underwater exhaust, or strut keels. My thought is if some of the exhaust was getting into the props it would cause a pulsating/shaking vibration, not a high pitch vibration. Seemed to be mostly on the stb side. Marlow's are nice boats with some good design features and this was the first time aboard one for us. They claim the keel strut design enhances water flow to the prop. I like the idea for prop protection but have not seen the design other than a metal boat that had metal tubes with supports and a skeg for protection. Also, I had done research on line and did not find many negatives other than mention of vibration on some earlier models plus being wet or not as good of ride vs another brand. Sounds like a problem that may not be fixable. Thanks for your comments about your experience with Marlow's.

Thanks ob. Sounds like this is a random problem specific to a hull#?

Thanks Capt J, funny I too was thinking if the exhaust dump was too far forward and even a small amount was sucked into the tunnels = cavitation/vibration. Just waiting to hear the results of repairs and new seatrial. Dang, you had performance problems with what size Offshore? One of my favorites, just hardly any 58 0r 62's on the market. Like the Fleming 55 but need more room inside and er. These RHP's are new too me, always had a sportfish.

Good comments and advice, no way will I chase a vibration on a boat for sale, did that once. Was gawking at a Fleming 65 at Bradenton a few weeks ago, wow! Makes a 55 look small.

That is some good speed @1500 on a 84. I can imagine those C32's are digging hard when accelerating fast. I do remember the capt going full throttle from about 1800. Not sure if that created the problem. The boat was 100 rpm from turning the 2300rpm by cat specs. Are the fences you mentioned similar to the faring buildup on the leading edge of a bow thruster opening?

We did look at a 63 Hat with 3412's had a great er. My last boat was a Hat sf with 3412's, great engines but was wanting inline 6's, speed is not a priority now. Did not like some things but overall a nice rig. You are right, much less maintenance, which has been a concern being a owner operator. I won't go into details but there are more issues with this boat from lack of use and deferred maintenance. Reviewing the maintenance records over the last 5 years got my attention, they are high maintenance boats. Everyone I have dealt with has been professional, answered all my questions, good to work with, and would hesitate to work with them again. There are a couple of other boats on my radar.

A Hat 63 with C18's would be a good setup. Have not seen one listed.

Pascal, your 84 has good performance and fuel burn. Thanks for those pics, never seen that fix. Interesting. Sounds like it cured your exhaust problem. Is this a common problem with underwater exhaust?