321 boom vibration

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AdamCermak

AdamCermak

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Oct 8, 2013
33
Beneteau 321 1999 Rose Haven, MD
When the main sheet is under load, e.g., under way or bearing down on it to furl the main (in mast), we hear a very loud, fairly high pitched vibration coming from the center of the boom (Charleston, I think). Taking load off the main sheet or manually pulling the boom to one side eliminates the vibration; reloading it, or releasing it when under way, very quickly reproduces the vibration. I can hear that it is definitely coming from inside the boom. While at dock we can certainly keep the main sheet a little slack, when under way that's not really what we want. Not an engine vibration (the vibration is present regardless of the engine's state), and not motion-driven (happens in the slip). I can't pick up on what would be driving this vibration, other than the wind obviously, and some harmonic of the boom and/or mast.
Has anyone run into this before? Is this too exotic and I should be talking to Beneteau or their boom supplier?

1000 thanks in advance for any thoughts!
 
DougM

DougM

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Jul 24, 2005
2,242
Beneteau 323 Manistee, MI
Rig tension? possibly the shrouds and backstay are not properly tensioned, and you may be getting a harmonic vibration that is really telegraphed from the mast. That's just a wild guess on my part.
It could also be the outhaul tension. The lines inside the boom may be acting like a guitar string. Is the vibration still evident with the outhaul completely eased?
 
RichH

RichH

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Feb 14, 2005
4,773
Tayana 37 cutter; I20/M20 SCOWS Worton Creek, MD
DougM offers a good possibility - induced harmonic vibration.

Suggested Rx.: Check mast 'pre-bend' and retune your rigging.

That you can change the frequency of this vibration by stressing the boom with the mainsheet tension, suggests its the boom is vibrating in response to such a vibration elsewhere on the boat - its probably 'responding' (as a harmonic) to an errant vibration in the mast/rigging system . High frequency vibrations usually means that 'something' in the rigging is 'too tight' --- backstay maybe?

To change such induced harmonics to where they are 'benign' or cant be heard
1. ... change the mass of (add or remove mass from) the boom - as a trial simply hang a moderate weight from the boom midspan. If that changes the 'note', then consider to add some weight (lead slug, etc.) to the inside of the boom.
2. ... change the tension (force) on all things related to the boom - change vang pressure, change/vary outhaul tension, change/alter the tension/pressure on 'anything' that touches the boom.
3. expected best probable solution: Reset the rigging tension to 'proper tension', if that doesnt remedy this; then alternately, 'slightly change' the rigging tension in order to remove the principal vibration on the boat that is 'exciting' the harmonic vibration in the boom. see - http://www.riggingandsails.com/pdf/selden-tuning.pdf The most probable cause of mast/rigging vibration is lack of or improper set up of mast 'pre bend' or 'pre-bowing'. If you do have proper mast 'pre-bend', slightly increase the amount and note the change in the 'musical note' in the boom and that will indicate if the current prebow/pre-bend needs to be increased or lessened.

;-)


Rx.: Check mast 'pre-bend' and retune your mast rigging.
 
SoSound

SoSound

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Nov 21, 2007
673
Beneteau Oceanis 34 Kingston, WA
Where is that noise coming from?

As long as you're checking, you might as well check the points attachment for the various components, gooseneck, vang (both at the boom and at the base of the mast). Also check the shackles in the mainsheet rigging any other blocks you might have near the mast or boom. Any place where two pieces of metal make contact (even where the boom end caps are riveted).

We spent the better part of two years going to our YC outstation for impromptu overnights tied up at the dock, where we would struggle to sleep through the dreaded FENDER noise as the boat moved against them at the dock... SQUEAK, squeak, SQeak... You get the idea. Then one day last summer I got up to get something from the galley and FELT as well as heard the noise coming through the mast inside the boat! I looked outside and found that we were NOT moving against the dock at the time either...

Going up into the cockpit and on deck, in a matter of minutes, I managed to find that it was a very slight movement of the boom and changing tension on the mainsheet. One quick adjustment in mainsheet or topping lift tension is all we need to do now to quiet things down. And it only took us two years to find the cause!
 
B

Beneteau 321

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Oct 6, 2010
119
Beneteau Oceanus 321 Carters Pt.
We have a 1997 Beneteau 321 (new to us)Classic mast. We had a boom vibration + squeek
Tracked vibration to the topinglift --shackel that attaches toping lift to end of boom would vibrate creating a vibration/noise under way and at anchor even in light wind ,cured that wraped a length of tape around shackel.
Sqeek was goose neck removed same cleaned all joints then lubricated with winch grease and reassembled
 
cymeyer

cymeyer

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Jul 8, 2005
521
Jeanneau 389 Grosse Pointe Farms, MI
Beneteau 321 said:
We have a 1997 Beneteau 321 (new to us)Classic mast. We had a boom vibration + squeek
Tracked vibration to the topinglift --shackel that attaches toping lift to end of boom would vibrate creating a vibration/noise under way and at anchor even in light wind ,cured that wraped a length of tape around shackel.
Sqeek was goose neck removed same cleaned all joints then lubricated with winch grease and reassembled
Click to expand
We had the same problem and fixed it the same way.
We also thought it was in the boom until I held the shackle at the end of the topping lift....
 
T

terrykiwi

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Jul 11, 2012
12
Beneteau 381 Lions Head,Ontario
Had similar problem and it was the toping lift tension which we adjusted also the goose neck squeak we just tied off the boom to the toe rail with a preventer and that cured our issues
 
AdamCermak

AdamCermak

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Oct 8, 2013
33
Beneteau 321 1999 Rose Haven, MD
Thanks for the many comments, and sorry I've been silent - I'll be at the boat shortly and can report back on all these items. I'll see if I can locate and suppress the driver a bit and see if and how that changes the output. Embarrassingly, I haven't moved the dodger enough to get my ear up to the outboard end of the boom to inspect the shackle as the possible noisemaker, but if will.

Film at 11.
 
S

sailordoc89

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May 6, 2012
4
Beneteau O321 Deltaville, VA
just took care of my boom creaking with WD40 at the gooseneck. will try the tape on the topping lift shackle but where did you put the tape?
 
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