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Old 04-10-2015, 12:43   #16
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Re: Harmonic Vibrations on Aluminium Rig

We have the same issue at around 15kts at anchor on our Kevlar shrouds, definitely not our mast. I understand you can install dampers on them but I have been unable find them anywhere. I too would love to hear of a reliable cure.

Rob
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Old 04-10-2015, 18:13   #17
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Re: Harmonic Vibrations on Aluminium Rig

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Originally Posted by Emerald Sea View Post
Has anyone experienced where their Al mast and possibly rigging begins to make a 'humming' noise, while stationary, when the wind blows through it? I believe this is harmonic vibration (wind building up on the windward side of the mast/rigging and creating eddies in the vacuum leeward side i.e. vortex shedding). On my rig, it seems to start at about 10kts, it starts 'singing' and I can feel the high speed vibrations on the shrouds and mast. These are not excessive movements and its invisible to the eye. Certainly disturbing while trying to sleep! Its non-existent while sailing.

Has anyone come across this before and what have you done about it? Perhaps its a rig tuning issue and I need an TA (technical authority) to review it?

There is a related CF thread on this subject, good info, but it wasn't conclusive and was for a different rig.

Thanks

We have in-mast roller furling. Wind blows over the vertical groove and screams like the sound effects of a Halloween movie. I expect the headless horseman any moment. Its OK a anchor if we set head to wind.

I have also sailed a boat that was so well balanced that the keel or center board & rudder would sing. This can also excite the rig.
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Old 04-10-2015, 20:12   #18
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Re: Harmonic Vibrations on Aluminium Rig

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Originally Posted by Hydra View Post
Sometimes, the vibrations originate in the boom topping lift. Then, it is possible to suppress them, just by reducing this tension.

Alain
We get it as well. Sometimes just relaxing the vang tension helps as well.
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Old 05-10-2015, 02:03   #19
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Re: Harmonic Vibrations on Aluminium Rig

Interesting comments :roll eyes:

I haven't replied lately as its been pretty still lately with no winds at anchor however will do if and when I find a solution ... before the neighbours ask me to turn my monotone harmonic guitar playing off.

My rig is due for a series of tensioning checks but presently waiting till the next port to have expert tackle this but essentially the main shrouds are good and tight.

I will try adjusting the mainsheet/topping lift and see where this gets. Just need wind to re-enact it.

As for the Loos gauge, I have both 12mm and 14mm dia shrouds and understand Loose doesn't make a gauge for 14mm (correct me if Im wrong). Im still in the market for a 12mm or I just borrow from a neighbour.

We haven't a vang.

Thought about putting strakes (vortex repressors) on a few lengths of the shrouds to disturb the air flow which causes the vibration. In my previous life I engineered these for deepwater pipe spools in high current areas. Perhaps hydrodynamics and aerodynamics play to a similar tune here....need to look more into this.

I will update when I get a solution.
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Old 05-10-2015, 07:10   #20
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Re: Harmonic Vibrations on Aluminium Rig

Hi Emerald Sea,

I believe this is an issue particular to catamarans as I have never experienced this in a monohull.
Our Belize 43 have the same issue when moored and the wind is at an angle different to the cardinal degrees, particurlarly aft of the 90 and 270 degrees. Never experience this when sailing or swinging on the hook.

I do not believe the tesion of the rig can be done to remove this issue, but you seem to have a good understanding of vortex shedding around the mast and I believe this is where the problem is. It will be interesting to hear what you come up with.

I also have two friends with Mahe 36 cats that have the same issue.

Happy lead fre sailing from Lucky
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Old 05-10-2015, 08:21   #21
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pirate Re: Harmonic Vibrations on Aluminium Rig

It be the sirens, oooh aarrgh, they be a comin to get ya

It's the topping lift. I've tried dampening it, but to no avail. Wrapping another rope the entire length like strakes on a chimney might work, but I can't be bothered to climb the mast to do that.

Pleasant dreams.
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Old 05-10-2015, 09:28   #22
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Re: Harmonic Vibrations on Aluminium Rig

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Originally Posted by Emerald Sea View Post
Has anyone experienced where their Al mast and possibly rigging begins to make a 'humming' noise, while stationary, when the wind blows through it? I believe this is harmonic vibration (wind building up on the windward side of the mast/rigging and creating eddies in the vacuum leeward side i.e. vortex shedding). On my rig, it seems to start at about 10kts, it starts 'singing' and I can feel the high speed vibrations on the shrouds and mast. These are not excessive movements and its invisible to the eye. Certainly disturbing while trying to sleep! Its non-existent while sailing.

Has anyone come across this before and what have you done about it? Perhaps its a rig tuning issue and I need an TA (technical authority) to review it?

There is a related CF thread on this subject, good info, but it wasn't conclusive and was for a different rig.

Thanks
Your options are to change the weight or the stiffness to adjust the natural frequency of any structure.

Weight is fixed on your rigging so that leaves stiffness. Have you checked your tig tension. Do that first.

Then you could try a little tension in your halyard at different anchor points.

If its the rigging you might be able to see the standing wave. Our spinnaker halyards do this. Wrapping them around the furled jib eliminates this.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app
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Old 05-10-2015, 18:25   #23
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Re: Harmonic Vibrations on Aluminium Rig

I did get that humming in boats I've owned with topping lifts on the boom. Vibrations disappeared when I fitted my present yacht with a sprung kicker supporting the boom. As others have suggested its likely the topping lift causing the humming. Instead of replacing your topping lift, you could easily try adding an additional couple of metres or so of a larger or smaller diameter cord to the bottom of the existing topping lift line. That should detune the vibrations. If it doesn't work you can easily go back to the original without having cut anything. Just tie it with a knot until you get a good result. Then you can splice it if you want to.
I don't thing the rigging wire makes a humming noise in the wind. It does of course whistle in the rigging as is obvious at a marina when the wind is 20 knots or so. That's the sound they dub into some movies. We get it for free.
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Old 05-10-2015, 18:44   #24
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Re: Harmonic Vibrations on Aluminium Rig

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I don't thing the rigging wire makes a humming noise in the wind
Ours is definitely, 100%, the shrouds. If you touch it lightly with a finger the vibration is incredibly rapid. Touch it more firmly and it goes away.
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Old 05-10-2015, 18:51   #25
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Re: Harmonic Vibrations on Aluminium Rig

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Ours is definitely, 100%, the shrouds. If you touch it lightly with a finger the vibration is incredibly rapid. Touch it more firmly and it goes away.
Thanks. Well I haven't checked every boat. Maybe if its a problem to you, you could fit those snap on plastic tubes to the bottom of your shrouds. I have them and like the look and they are good to hold onto. They might dampen the vibrations?? Im quite sure though other people don't like them.
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