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  #1   IP: 71.244.241.97
Old 05-06-2018, 10:19 AM
sdemore sdemore is offline
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Vibration Problem

Question on what to check in my drive system. On this C&C 30 project boat I got, the engine runs really smooth until I put it in gear. I rebuilt the engine when I got the boat last year and it has now been in the boat for about 8 months. When I started this process, you could certainly feel a vibration, but not a bad one. The shaft alignment is dead on. The drivetrain now has about 20 hours on it and each time, the vibration gets worse. It is now to the point that the lids on the cockpit lockers rattle and just makes a terrible noise and feel. There is no vibration when you shift into neutral.

This is my first experience with a sailboat (or an inboard), so I am still learning. When I put everything together, I dug everything out of the stuffing box and packed it all the way full. I had to adjust it pretty loose (barely finger tight) to get any water to drip through. I put ablative paint on the prop, but it doesn't look like it has changed to throw things out of balance.

Any suggestions on what I should be checking? Can you over pack a stuffing box, could the cutlass bearing be going out and causing this? Any other thoughts?

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Steve
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  #2   IP: 155.186.126.158
Old 05-06-2018, 10:43 AM
Dave Neptune Dave Neptune is online now
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Steve, did it vibrate at first or did it start after a while? The vibration could be a miss fire in the engine or the prop shaft shaking around. Take a good look at the shaft to see if there is any wobble. Have you or can you get you hand on the packing while running in gear? If so you should feel the vibration there if it is the prop or shaft. This could be as simple as something is caught around the prop not an uncommon way to "develop" a vibration. Take a look at the prop somehow.

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  #3   IP: 71.178.85.102
Old 05-06-2018, 11:42 AM
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If you did not replace the cutless bearing and everything else is in order as you've described, then that would be something to check, especially if you have no history.

As Dave suggested, confirm the prop shaft is straight and not "whipping" by grabbing onto the stuffing box to feel for it in gear.

One other question..fixed prop? Folding props sometimes do not flop out exactly the same, which can cause terrible vibrations until they are even.
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Old 05-06-2018, 11:48 AM
JOHN COOKSON JOHN COOKSON is offline
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Maybe the engine mounts are loose.

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Old 05-06-2018, 11:13 PM
sdemore sdemore is offline
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Dave, it has always with my very limited experience) had a vibration. It wasn't originally this bad and has been getting worse each time I run it. If I am motoring along, feeling the vibration and shift into neutral, it goes away. It doesn't feel like an engine thing, but I suppose it could be. I'll also see if I can get my GoPro down there to look at the prop.

Shawn, fixed, 2 blade prop.

I'll see if I can get a hand on the stuffing box next time I'm out. The C&C's (at least this one) have a piece of angle aluminum over the stuffing box to lock it in place, and I can't remember how much of it is accessible.

What I don't hear (so far) is that it could be an overpacked stuffing box.

Steve
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Old 05-06-2018, 11:49 PM
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Steve,

If you aligned the shaft when the boat was out of the water, or just recently put in, things can change over time. Being on stands on the hard puts loads on the hull in different places than when its in the water, and the boat will often "relax" back into a slightly different shape, throwing the alignment out.

Try disconnecting the shaft flange at the engine and rechecking the alignment.
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