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Troubleshooting Vibrations

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outobie

Regular Contributor
Hi all. I’m hoping the knowledge trust can give me some ideas on what to look for to troubleshoot this

i have twin 2001 5.7 2bbl alpha one gen 2 engines

last Sunday while coming up on plane at 2800 rpm at 22kts after anchoring for lunch I heard and felt “thunk”.

i immediately powered down and shut of the engines.
i thought I hit something. I was in 12 foot of water and couldn’t see anything I may have hit. I raised the drives and laying on the swim platform, ran my hand down all the leading edges of the propeller blades and the bottom self of the outdrives and the prop shaft housing as far up as I could reach. There were no discernible knicks or bends or any damage I could identify.

not finding any damage I decided to make my 90 minute run home. On the way back I could feel a vibration through the hull and while turning the steering wheel. The boat seemed to run fin so I thought perhaps I just imangined the vibration.

fast forward to this week and I’m convinced the vibration is there and wasn’t before.

my boat is wetslipped and I don’t own s trailer.

question: is there something that could have come loose inside the motor or drive that could have caused these symptoms? I still don’t believe I hit anything.

what would you suggest I look at and is there anything I can do or test for with the boat in the water?

thanks for any suggestions
 
Been there, done that.

Many years ago, we inadvertently entered a gigantic debris field in the Chesapeake Bay, a mass of floating crap that was miles long and extended nearly shore to shore. Hit a submerged plank that killed both engines (twin inboards). Restarted and limped out of the debris, then planed off gently and crept back home.

I was absolutely POSITIVE we had at least one bent shaft/ dinged prop/ etc. Had the boat hauled out and...everything was in perfect condition. But I was SO positive something had been damaged. Get the point?

Hope that's the case here.

Jeff
 
Yeh that would worry me no end until I was sure. I think you have to pull the boat and check the drives.
 
Yeah I plan to have it hauled

Yards are busy this time of year so was hoping for some ideas I could test for with it in the water

i put 6 hours on her this weekend and I did notice that the vibrations seem to be at certain speeds. They are the worst of course at my usual cruise speed of 22 knots at 2800 rpms.

the vibrations seem to be significantly less at 3200 rpms and 27 knots.

maybe I should just run faster��

i sure would feel better if I could find evidence of a strike on one of my props. Then I could stop worrying that there is some imminent internal failure about happen that sinks my boat
 
Update... bent blade on stbd prop.

a friend let me use his lift to inspect.

Sure enough one blade had a good bend in it... no knicks or paint missing but a good bend. I swapped it out with my spare prop and am back in business

tje spare is a little rough so I’ll just use it till I can get a new one

sure do wish I could have the old one repaired... seems like a waste to throw it out. New ones are only $140 so I guess they aren’t worth fixing
 
Thunks usually leave evidence....though its not easy to find....glad you found it....

Food for thought - if your buddy lets you use the lift for the next prop swap, you may want to bring a power washer with you.....being wet slipped, I'd bet on some growth since the water has warmed....
 
Yep hull was perfect not a spot of Growth on the hull a couple tiny barnacles on the outdrives but all the aluminum anodes, stainless trim ram hoses, and transducer had a layer of slime and growth that I took care of when changing the prop. The paint my shop used this year seems to be doing s good job so far

better than last year by far
 
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