mast resonating

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robertj

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Our first outing this year was marked by a humming, no sound outside but inside the cabin. Investigating I found the mast to be resonating and thus amplifying the sound inside the cabin to quite a noise.

My question is anyone else witnessed this and if so how to stop it?

bob
 
Think of your mast as the neck of a guitar... with loads of strings and you sitting in the case.... /forums/images/graemlins/smile.gif
Every boat I have been on does it... less tension in the mainsheet can help.... as the sound seems to actually come from the boom.... I take mainsheet off of our normal attatchment point in the cockpit and run it off to a point on the pushpit with less tension in the sheet... in the past with a coaschroof mounted main sheet I have run the sheet out to the limit on one side of the travleller, then used another line from the boom down to the other end of the traveller to secure the boom in thecenter but with very little tension on the main sheet... I also find that their is less noise if the cover is on over the front of the boom and around the mast.....

/forums/images/graemlins/smile.gif /forums/images/graemlins/smile.gif


Wait until you try to figure out the noises from the little shrimps popping under your hull at 2am......
 
I find its the topping lift that resonates lots for me, I wind my main halyard around the topping lift and its stops resonating, similar to the earlier suggestion for the mast
 
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Think of your mast as the neck of a guitar... with loads of strings and you sitting in the case.... /forums/images/graemlins/smile.gif
..

[/ QUOTE ]

Little bit surprised and suspect it isnt the mast but the rigging both standing and running. There's a reason they dont make bells out of ally and its because it deadens sound rather than resonated.

Have a play with all the various components. If its a change since last year it needs following up cos it might just be a warning of something wrong.

My mast doesnt resonate but the loose boards by the engine do with a vengeance
 
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Ours was after setting up the rigging this year. Stopped it by relaxing the backstay.

We have also experienced topping lift thrum, but this does not resonate down the mast as much. Again, taking some tension out of the system - eg by relaxing the mainsheet a little - should fix it.

- W
 
Maybe the bearing in the wind transducer is wearing and transmitting the noise down the mast??.........that said you would hear that even if not sailing.
 
Whn you go round the boat feeling every halyard and piece of rigging you will discover which item is resonating. Ease the tension, or tune it to B flat for a more harmonious accompaniment.

I'll guess the boom lift is the cuplprit.

If the mast is pumping in strong wind, you have setup problems - tension the rigging!

PWG
 
My race boat in Tallinn was terrible. In fact previous owner had snapped the mast with it when pushing her too hard and ignoring it.

When I had the boat - we installed a second baby stay inside the normal forestay .. which went from crosstree level to just aft of the foredeck mooring point. This stopped it completely and also gave us an extra adjustment to the mast shape.

Another boat - sister to ours they found that altering certain stays would stop it - but they had slightly shorter mast and also crosstrees were set higher than ours.

To find the culprit - is a matter of going round boat and leaning on ropes / stays etc. till it reduces or stops ... then finding what to do with that one ! Bit like a niggly rattle in a car !
 
Depends what you mean by resonating. Ours was pumping in high winds and the vibration could be felt down below. The solution: tightened the lower shrouds. They were too slack and not controlling the middle part of the mast correctly.
 
If the mast is pumping then it is "Vortex shedding". Wikipedia explains it all, including this nice animation.
Vortex-street-animation.gif

To fix this you need to alter the profile of the mast. The fender up the mast is a solution for this. The solutions which involve tightening/loosing rigging could also help - if they change the profile of the mast in the wind.

If it is just the rig humming then loosening something off usually works - typically the topping lift or the mainsheet.

EDIT to say. Also the wrapping the halyard round the mast should help the pumping. However, I have never got this to work because the spreaders are in the way and prevent wrapping above a certain height.
 
A lot of the humming I've found comes (as suggested above) from the topping lift attached to the end of the boom...couple of other ways:

Release the main sheet a bit so the topping lift isn't as tight

Tie a short loop of rope to the end of the boom and attach the shackle to that instead of the metal fitting on the boom

Hope that helps

G
 
thanks all not been down yet to try but tomorrow is the day to try and sort it will let u know what happenes.


bob
 
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