Boat Vibrating - Really need your guidance!

KnotConnected

Petty Officer 1st Class
Joined
Aug 15, 2012
Messages
221
Hey all!

This past Sunday we took the boat out with some family, 6 people total (more than I've had before). I ran the boat about 10 miles out to the lighthouse and back at ~3400 RPM. About an hour trip in total. About halfway back to the dock I noticed some vibrating from the back of the boat. Not super violent, but certainly noticeable (My GF noticed it too, but didn't want to mention anything until we were back at the dock). I think I *may* have hit something small / light earlier on, because i did hear a subtle thump and noticed the anchor bounce in the bow pulpit, but at the time shrugged it off as just a wave that hit us wrong.

The vibration went away as we throttled down. There is also no mechanical noises or apparent engine issues, everything else seems to run and sound fine. I checked the gear lube back at the dock, and the reservoir was down about 1" from the line (it was right at the line when we left) which has me worried. I lifted the drive in the water and inspected the props, but didn't see anything glaring. I checked the drive lube the following morning, and it was still about an inch down.

History: This winter I had the marina replace the U joint assembly, U joint bellows, gimbal bearing and some seals. I took the boat up river twice this year, but each cruise was about 30 minutes and we never went much beyond idle. This was the first time we had it up to WOT and had it at cruising speed for a while (whole boat ride was about an hour).

The real SOB is we're planning a 4 day trip about 60 miles up the bay in 2 weeks, and I won't be up on the boat until then...

Any ideas what the issue could be? Could this be a prop or drive alignment issue that the marina botched that just surfaced now that we had some time on the boat at speed? Is there anything I can check or rule out without pulling the boat out or cracking the drive off? Could the lower drive lube just be from running the boat at speed for a while since it was filled?

Also, is this the kind of thing I could just put off until after the trip, or should vibration like this be taken pretty seriously?

Thanks everyone! As always, I super appreciate your help and guidance!!!
 

sogood

Petty Officer 1st Class
Joined
May 11, 2016
Messages
361
Just a thought, but if you think you may have hit something, might you have damaged/ misaligned the trim tab? It might add to any vibrating.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
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Jul 23, 2011
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47,300
Is there anything I can check or rule out without pulling the boat out or cracking the drive off?

Nope. you are going to have to put it on the hard and pull a drive.

yes it is serious

avoid shipyard marine
 

Grub54891

Vice Admiral
Joined
Jun 17, 2012
Messages
5,908
The drive lube was low, more than likely because it was serviced recently, the drive is self filling, and there is an air pocket in in the upper drive at the top, when you run it the air pocket works its way out and then you have to top off the reserve reservoir. As far as the vibration, yeah, you have to pull the boat and have it checked out. Hopefully just a bent prop.
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
I'd be looking to see if your prop is fouled with something (rope?) before you let this get too complicated.
 

Mischief Managed

Lieutenant Commander
Joined
Dec 6, 2005
Messages
1,928
Check the 4 engine mounting fasteners for proper tightening before you pull the boat, might be an easy fix...
 

KnotConnected

Petty Officer 1st Class
Joined
Aug 15, 2012
Messages
221
Thanks everyone!

I'm going to make a long day of heading back up there tomorrow and running the boat to see if its still happening, happens when trimmed up, down, etc, and pull it out if need be.

Anything I should check while we're running the boat? Additionally, is it bad / unhealthy for the engine to run it up to 3k or 3500 RPM in neutral while at the dock?
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
Would only take a minute to tilt the lower unit all the way up so you could have a good look at it. Checking to see if the prop is fouled with anything or has one blade folded over should be pretty easy, without even leaving the dock.
 

KnotConnected

Petty Officer 1st Class
Joined
Aug 15, 2012
Messages
221
Thanks Ahicks. I did trailer trim the drive this weekend. Nothing glaring, but the water in the marina doesn't give me more than an inch's depth of visibility :-X
 

mr 88

Commander
Joined
Nov 3, 2010
Messages
2,115
Anything I should check while we're running the boat? Additionally, is it bad / unhealthy for the engine to run it up to 3k or 3500 RPM in neutral while at the dock? [/QUOTE]
What would the reason be for revving it that high ? In my world I keep it below 2,000 if I have to rev it up for whatever reason. I guess it would be like putting your car in neutral and basically flooring it, things have a tendency to come apart under the circumstances. Yes it's "unhealthy " unless your in the mood to rebuild your engine.
 

ahicks

Captain
Joined
Sep 16, 2013
Messages
3,957
Do you have a swim platform? Maybe crawl out on that and do some feeling around.If they're a split design with one on each side, turn the wheel hard over so the lower unit is closer to one side.
 

wahlejim

Master Chief Petty Officer
Joined
Jul 23, 2015
Messages
884
symptoms that you have described:

1) Vibrating at higher RPMS
2)Loss of Gear lube at higher RPMs, but not while sitting
3)Possibly hit something

3rd symptom is easy to check. The weakest parts of your outdrive are your prop blades and skeg. Even if you can feel them, you should be able to tell if they are damaged. That is an easy check. Even if you have to get wet to do it. That would cause the vibrating and you can chalk the gear lube up to an air pocket IF you don't lose any more.

Unfortunately, if there is no damage down there, I would go back to your u--joints and seal around the u-joints. It sounds like they are not aligned properly or installed properly. If the u-joints are not installed correctly, it would cause the vibration issues you are having. Also, they will wear the seal away in no time, allowing gear lube to leak into your bellow, causing your reservoir to drop.

To check the u-joints, you will have to pull the boat out of the water and pull the outdrive. Check the u-joints for any play and check engine alignment. Look in the bellow for any gear lube. you will have to be able to tell the difference between gear lube and grease from the u-joints.

At this point, I would not run the boat as is. You run the risk of ruining your outdrive and or engine. It just isn't worth it.

A previous post mentioned checking the mounting bolts on the engine. That is a good diagnosis to check for a possible issue, but if theyare loose, it is not just a matter of tightening them. You will have to pull the boat and the outdrive and use the tool to align properly.

Let us know what you find
 
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