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Old 05-06-2018, 11:19 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?

Steve Demore
S/V Doin' It Right
Pasadena, MD
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Old 05-06-2018, 11:43 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.

Dave Neptune
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Old 05-06-2018, 12:42 PM
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sastanley sastanley is offline
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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.
"Twice Around" - '77 Catalina 30, #511 with original A-4 & MMI manifold.
She is always happy with a clean bottom!
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Old 05-06-2018, 12:48 PM
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Maybe the engine mounts are loose.

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Old 05-07-2018, 12:13 AM
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 Demore
S/V Doin' It Right
Pasadena, MD
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Old 05-07-2018, 12:49 AM
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edwardc edwardc is offline
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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.
@(^.^)@ Ed
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with rebuilt Atomic-4

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Old 05-07-2018, 01:35 AM
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2 cents

The guys have mentioned the main culprits of a vibration. I'd check in this order.
1. Foreign object on shaft or prop...sometimes a plastic bag on the shaft is worse than a rope wrapped around it..underwater camera might get you a good look at things.
2. If folding prop it can be an issue. (I know you don't have one but will put this in incase someone reads this thread later)
3. Barnacles on prop...again needs to be checked.
4. Engine issues. I've issues with severe vibrations that were caused by incorrect plug wiring sequence and a bad coil. The coil was most common, I've seen a couple of them and it rattles so bad that the person thinks a bearing or something has gone in the gear box.
5. Cutlass bearing possible but it's generally something that gets worse over time, but not suddenly worse.

On a hunch, and the rattling you are describing...barring an obvious foreign object on shaft ...look very hard at the wiring, cap, plugs and coil. Believe it or not, the coil can make it happen but it usually runs well for about 10 minutes then the racket starts.

I think it was Joe Miller, one of our members here on the forum, that called me one time. He was headed on an excursion and the boat was acting up.
...was rattling, vibration etc. He pulled into our yacht club. We fooled around with a lot of things figuring that one out. New coil and went on his trip without any more issues.

1976 C&C 30 MKI

The pessimist complains about the wind.
The optimist expects it to change.
The realist adjusts the sails.
...Sir William Arthur Ward.

Last edited by Mo; 05-07-2018 at 01:52 AM.
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Old 05-07-2018, 11:34 AM
Marty Levenson Marty Levenson is offline
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If none of Mo's ideas lead you to the cause I would double check the alignment.
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