Troubleshooting running gear vibration

I apologize for jumping in late on this thread. From personal experience I know how challenging/frustrating it can be identify the cause of vibration.

I'm assuming that this vibration didn't occur when the boat was sea-trialed in Ft. Lauderdale prior to purchase? A key assumption.

If vibration was absent on the sea trial, I'd suspect that the cause could have been handling during shipping, impacting the running gear in some manner (you mentioned it had been moved on the ship). I acknowledge your statement that you'd prefer to avoid having to haul out. Unfortunately the expense may be necessary. Operating with my key assumption, it's where I'd have started. Once on the hard a thorough inspection can be done. More thorough than a diver can. It also presents an opportunity for an overall hull inspection/cleaning and bottom paint if needed/timely.

Having been there, I appreciate the challenge you're dealing with. Good luck.

P.S. Is this boat ex "Bluewater Beth"?

Actually he said it happens between 1400 and 1600 rpms, a place they wouldn't have spent much time at during the sea trial. So it may well have been present; just not noticed.

Good point. I have limited experience sea trialing boats but I wonder, wouldn’t you notice vibration as you moved up through the rpms? Particularly on a sea trial when you’re acutely focused on identifying any issues?

P.S. I’m learning a lot from this forum and particularly from posts such as yours. Thank you.

P.M. me, I have some info

At that rpm he'd be climbing on plane. If I were trying to sell a boat with this issue I wouldn't hang in that range to show it off. Add to that most of the buyers I've looked at boats with are in love and we all know how much we'll overlook for love.

It most likely has a lot more fuel and weight on board now and as it’s trying to get onto plane it presents itself. It’s a Taiwanese hull, many will exhibit vibration in that rpm range

From one motor?

yeah, probably induced by the stabilizers and if I remember correctly boat has/had a list and flops over to one side at cruise without the trim tabs, they probably got shaft placement, stabilizer place,ent or something off an inch......

Good thought about the stabilizer. I still think it's more likely between the alignment and the shaft but that's a definite possibility.
Holding at every 200 rpm could still have missed it since it's in a 200 rpm range.

I have a 1990 Ocean Yachts 48' MY with a shaft wobble & vibration on the port side along with a rattle over 1500 rpm at the stern/rudder area which is also on the port side.

One thing I have learned is that having a boat on stands and blocks can affect the shaft alignment. Having your boat shipped could have affected your shaft alignment. My shaft wobble & vibration lessened after running a couple days. In my case I could have motor mount issues.
Capt J, you mentioned that underwater exhaust could cause the vibration. How does that happen and what would be the fix?

My boat is currently hauled at Lamb's Yacht Center in Jacksonville FL. They were not able to track down the rattle and are guessing it is the trim tab. I don't believe that is the problem. The trim tab is just a thin sheet riveted to the hull with a hydraulic piston that moves it 3" max, and I don't use it on the port side because the boat lists to the port. My question if I remove that tab altogether (to eliminate that possible rattle source) and leave the starboard one how would that effect the boat running underway? The reason I am considering it is that I plan on installing the Zipwake system and I feel the current system is almost useless.
I will create a new post to ask about my trim tab so post any responses there.

You are talking a whole different scenario with your trim tab questions. Suggest you start a new thread and you will likely get better input and then not hijack this thread. And as for alignment while out of the water, this is correct. You can do a preliminary alignment on the hard but you need to be in the water for at least 24 hrs. before doing a final alignment. When on the hard your boat sags and/or deflects as it is only supported in the blocked locations. When in the water, you are supported by the entire wetted surface. This changes the deflection of the hull and effects your shaft and strut alignment.

Thanks and yes I started a new thread

Does the vibration occur at the dock without a load, transmission in neutral?

If it does, and if you're comfortable with a wrench...you could release the coupler bolts at your gear, and create, say, 1/4" between the flanges using what you can find aboard and handle as a reasonably reliable spacer. Watch that gap, and spin the shaft while paying attention to changes in the gap or the angles of the face of the flanges. If there's an alignment issue it may well be seen easily as 1200 is a fairly low RPM.

At this point you can start the engine with the shaft gapped as before, and this time repeat the run with the gear engaged to see if you have vibration caused by the gear.

If you clear both vibration tests your issue is within the running gear. Could be a shaft or prop (or alignment). Could be a bearing, too.

Good outcome. You need that vibration gone...