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Dave Montgomery 04-29-2013 05:54 PM

Strange noises from below...
No, I do not need a Rolaids but thanks for asking :o.

Just bought a 1990 C&C 34+. When motoring at lower rpms, say about 1000-2000, there is this kinda irregular thumping sound which I can feel in my feet and hear. It is not loud and not shaking the boat but still a concern. Just had the boat out for survey and the shaft etc. "looked all right." Boat has a dripless seal which all seems to be in order. Motor mounts seem OK, not a buuch of movement. The sound does seem to be moderated by rpms though. Also, it has started to make a chirping sound, also effected by rpms. At first I thought this could be the fan belt or water pump/alternator but those seem OK.

Could the shaft seal make such noises and vibration? Ideas?


krisscross 04-29-2013 06:01 PM

Re: Strange noises from below...
Cam shaft? My truck has that problem. Been like that for the last 30,000 miles.

sailvayu 04-29-2013 06:36 PM

Re: Strange noises from below...
Do you have a folding prop? mine used to make noises like that have a fixed one now and no noises.

n8kraft 04-29-2013 06:45 PM

Re: Strange noises from below...
My boat resonates when the engine is running at an idle, 800 to 900 RPM, then everything settles down at higher RPM.

SchockT 04-29-2013 08:37 PM

Re: Strange noises from below...
I experienced a chirping noise like you described, and found it was a loose zinc on the propshaft. You may also want to check your cutlass bearing. If you have a folding prop, it may have some slop in the blades, or it may not be opening properly causing an imbalance.

BarryL 04-29-2013 08:41 PM

Re: Strange noises from below...

The thumping sound is a classic symptom of worn cutless bearing.

Good luck

tdw 04-29-2013 08:44 PM

Re: Strange noises from below...
After our last haul out for anti fouling in November our girl developed an odd thump thump when in reverse. This with a Flex-o-Fold prop. She was again hauled late March for another reason and while she was out I gave the prop a really good going over to make certain it opened all the way out and had no obstructions. Since going back into the water the noise/vibration has stopped. I am told it could have been cavitation caused by the prop not fully opening (possible something caught up inside) and went away after I had cleaned away the obstruction.

Soooo .... if you have a folding prop maybe same problem. If fixed prop simply ignore everything I have just said.

SloopJonB 04-29-2013 08:47 PM

Re: Strange noises from below...
Do you have frisky couples on board when you take the boat out? :D

benesailor 04-29-2013 08:52 PM

Re: Strange noises from below...
If you can feel it in your feet you most likely have an engine/shaft alignment issue and/or possibly a worn cutlass bearing. I don't no what the chirping is; hamsters?

T37Chef 04-29-2013 09:35 PM

Re: Strange noises from below...
cutlass bearing...hopefully you haven't damaged the shaft yet, if so it may need to be replaced as well. Looks like a dive or haulout

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