HotSnail

Dynema standing rigging howling in the wind

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I recently changed the standing rigging I’m our boat to Dyneema. Rigging and tensioning went great, the stays keep the spar upright so so far so good. The problem we have with them is that the rig is extremely noisy. It starts at something like 6kn of wind and doesn’t stop after that. At the lower wind speeds it’s a low hum, not really annoying but as the wind picks up it gets more and more noisy to the point you have to raise your voice and pumping of the spar.

Is anyone here familiar with this problem of dynema rigging, and if so, how have you solved it? So far I found changing the tension (has not helped so far) and adding a helix of a thin dynema line around the stays. Anyone other ideas, suggestions or experiences?

 

cheers, Jan

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Pumping of the spar??? Not enough tension IMHO.

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Change the harmonic frequency. I’ve seen boats use archery dampeners. Not pretty but it helps

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2 hours ago, mgs said:

Change the harmonic frequency. I’ve seen boats use archery dampeners. Not pretty but it helps

They are way beefier than bow string dampeners. I will try to post a picture if I can find one. Got some somewhere. 

Backstay still hits a harmonic frequency now and then (no dampeners), but change the tension a bit an it quiets right down.

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I had this issue on my Etchells (non class) with a dyneema backstay.  With the hollow Etchells the boat hummed like a Drum!!

I found a small length of hose, split and fitted over the dyneema fixed it.

Out of interest I have rigged a couple of boats with Dyneema and it's never been an issue.  Do you have chafe guard over the stays as both boats I did have

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There is no cover on the rigging, juist 5 and 6mm dynema core.  For the pumping of the mast I described maybe pumping is not the correct word. That doesn’t happen under sail, but the spar starts to resonate heavily with the stays....

I’ll have a look at the archery dampers. On the Dutch sailing forum a piece of shock cord spiraled around the stay was suggested, approximately 1 to 1,5m long halfway the stay. I’m also going to try that idea. Thanks for the suggestions so far!

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Go for the spiral. It is the default solution for such resonance problems.

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Maxis and TPs etc with composite rigging use foam pipe cladding/insulation for a simple solution to the resonance - theirs typically include a zipped cover around the foam so they can be easily taken on/off and the foam doesn't shit the nest too quickly.... your local sail/cover maker should be able to knock something up or just tape the bare foam around the shrouds...

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going to try the foam ..... we currently use sail ties and lash tighten the shrouds with frapping turns to change the harmonic. It is really annoying when there is no wind when you anchor and you dont do it and then the wind picks up at 0200 and everything starts humming

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Foam ist way overkill in my opinion. All you need to to is break the symmetry of the shroud cross section. A very small diameter line spiralling around the shrouds will do the job and most likely be cheaper and longer lasting than foam.

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1 hour ago, neuronz said:

A very small diameter line spiralling around the shrouds will do the job and most likely be cheaper and longer lasting than foam.

He's already tried that, according to the first post. Perhaps a greater diameter line?

Darned von Karman effect!

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I think I was unclear in the first post. I didn’t try the winding yet, wanted to be a bit more sure that it would work since it’s a fair amount of work with the rig standing. I only found about it in one post on a forum so wanted to doublecheck.

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1 hour ago, HotSnail said:

I think I was unclear in the first post. I didn’t try the winding yet, wanted to be a bit more sure that it would work

D'oh!

Yah mon, wrap it.

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Just a thought, I have used 2mm dyneema as a wrap for chafe guard on the stay, looks like the old galv rigging!!  I use some clear super glue to hold the start and end in place

So maybe you could kill two birds with one stone?

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Does it stop the rigging from resonating? It probably takes quite a bit of 2mm to wrap a stay?

I think it would be a bit of a job to do with a standing rig. might be something to do when the rig goes of after a couple of years :)

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21 hours ago, neuronz said:

Foam ist way overkill in my opinion. All you need to to is break the symmetry of the shroud cross section. A very small diameter line spiralling around the shrouds will do the job and most likely be cheaper and longer lasting than foam.

This is interesting and sounds like a better long term option - the foam I mentioned is effective but isn't intended to be left in place - they get zipped on as soon as the boat finishes sailing so are more labour intensive.

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6 hours ago, HotSnail said:

Does it stop the rigging from resonating? It probably takes quite a bit of 2mm to wrap a stay?

I think it would be a bit of a job to do with a standing rig. might be something to do when the rig goes of after a couple of years :)

You just need to wrap a helix of the small stuff around the stay. More info here:

https://physics.stackexchange.com/questions/75459/why-do-chimneys-have-these-spiral-wings

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I'd be inclined to try a rubber ball, slit halfway, hung around the stay and fastened with tie-wraps. Then move it along the stay to "detune" the resonance - the lengths on either side of the ball NOT being simple multiples. Like a finger touching a guitar string ...

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A hollow ball will probably be more difficult to keep in place than a "solid" ball - like a stiff foam filled one .

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15 hours ago, hdra said:

What is it about synthetic rigging that makes this so much more of an issue than with wire or rod?

It's like ratchet straps holding down a mattress on the roof of the car. Put a bunch of twists in them and they look like junk but are nice and quiet. Lay them flat and have an OCD moment getting them all neat ant tidy and they howl like you got a cat by the balls up there. It has to do with airflow and the resonant frequency related to tension. Mitigating the frequency removes the issue. 

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3/4 full water bottles taped to the rig is what we've used on EC6. Have heard it works on dyneema also.

 

Almost every raceboat with carbon rigging has bungee spiralled and taped around their runners...

 

HW

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