Don't know whether it's a result of my new forestay, my new dyneema uppers or the general setup of the mast with far less pre-bend than previously but the damn mast sounds like you are blowing across the top of a bottle most of the time while at anchor in a light to medium breeze. It resonates higher and lower and can also be mistaken for a jet ski noise.

You can feel the vibration when you touch the mast. I'm going to tie various halliards down to different places along the toe rail tonight to try and get rid of the noise.

It is a seven eights trailer sailer mast which is quite tall but very small cross section.

Has anyone got any other suggestions? It's infuriating when you're trying to sleep.

I get that exact sound as well. For a long time, I dismissed it as prop noise coming through the hull. Then I rested my head against the lower should and felt it vibrating really fast. It's the weirdest thing because none of the other wires do it. I think it's probably harmonic resonance due to the wind. Wrapping something heavy around the wire might dampen the vibrations.

Had the same problem with roof/ladder racks - resonance at certain speeds = ascending hum !
Solution was to ensure smooth taper on leeward side,which was available with certain brands - promac .
Not an aeronautical engineer,but ? insert solid taper/luff line into mainsail track - (clark rubber has many profiles .)
(Just trying to be helpful,as been washed out for weeks /getting mouldy !- have to get inside job !?)
Mason

Cant remember which charter yacht it was, but the topping lift was small gauge Dyneema and it sung, vibed the mast an annoying pitch. I ended up with the lazy jacks taking most of the weight and the boom lashed preventer style outboard to stop it wiping the dodger off. If it was me even if I had to de tune the rig overnight I would, looks like nice weather there enjoy

Make a temporary boom crutch for a night, take all tension off topping lift. I think it's likely it the topping lift singing. My Elliot used to be very bad for this noise.
Alternativly tie shock cord from shrouds to mast. The shock cord generally stops the resonance.

Topping lift? If you ease the mainsheet can you get it to change pitch?

It could be any part of the rigging or even the mast itself. Shock cord is an interesting idea, and lead shims may also work. Just need something that shifts the natural frequency slightly. Someone needs to make a video about this effect. I couldn't find one on Youtube except for shaking flagpoles and the Tacoma Narrows bridge.

My mast used to occasionally pulse and vibrate on anchor. The fix was to raise a fender up on the halyard and secured to a fixed point on deck so it was tight against the mast. Worked perfectly in stopping the noise and became a talking point in a few anchorages. The trick is to find the sweet spot on the mast to disturb the harmonic motion. We do something similar on wind turbine towers.

Thanks guys. My last night's effort with halyards didn't work so I'll try and put some of your ideas to work tonight.

No luck yet. Not topping lift because boom on deck. Shrouds ocky strapped to each other and fender up mast. Might try raising the fender a bit higher.
The problem is more likely towards the top of the mast which is thinner as it is tapered but more difficult to stabilize the upper shrouds at that level.

Interestingly a mate with a dyneema strop to raise the pivoting keel on his small trailer sailer says that he knows when he hits 4 knots as the strop hums through the water.

For the observant I do have a solar masthead light but it gives up the ghost about 4 am so I get up for a pee then and turn on the Bunnings $2.50 job on the inner shroud. Previously pulled it up the uppers to the spreaders on a halliard but couldn't be bothered last night.

Ok if not the topping lift two other methods to potentially resolve the issue

Vortex shedding from the upper shrouds or mast is the likely problem causing resonance. Adjust the tension in the shrouds to change the natural frequency of the wire. It helps if you can do this in the wind with reasonance occurring with the help of a Loos gauge to make sure you're not overdoing it. Take care not to buckle the mast as a column.

If the mast vibrates, a solution is to wrap a rope around it in a spiral. At anchor hoist up your mooring line on the main halyard. Spiral wrap the mast to make a spiralling vortex breaker with the large diameter mooring line to reduce vortex shedding.Lastly if it's the upper shrouds above the spreaders, then next time before you raise the mast try spiral wrapping the upper spreaders with say an 6-8mm dia line, the aim again is to create a spiralling vortex breaker spotting the resonance.

Possibly the most famous example of this I know of in Australia is the Collin's Class Submarine with spiral wrap on the periscope to stop periscope vibrations from vortex shedding at speed. Same principle and it was a cheap and easy fix in the 90's.

Now if one were sufficiently nerdy, you could destructive interference to acheive a blissful silence, just record the sound and then play it back 180 degrees out of phase.
Or add a Marmalute to the crew roster?

Hey Jules, you didn't happen to bring the old wire rigging with you ?

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woko said..
Hey Jules, you didn't happen to bring the old wire rigging with you ?

Yes I did and stupidly on the boat too but can't re rig out in the islands away from the trailer and A frame and I'm not here long enough to justify going back to re rig.

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EastCoastSail said..
Ok if not the topping lift two other methods to potentially resolve the issue

Vortex shedding from the upper shrouds or mast is the likely problem causing resonance. Adjust the tension in the shrouds to change the natural frequency of the wire. It helps if you can do this in the wind with reasonance occurring with the help of a Loos gauge to make sure you're not overdoing it. Take care not to buckle the mast as a column.

If the mast vibrates, a solution is to wrap a rope around it in a spiral. At anchor hoist up your mooring line on the main halyard. Spiral wrap the mast to make a spiralling vortex breaker with the large diameter mooring line to reduce vortex shedding.Lastly if it's the upper shrouds above the spreaders, then next time before you raise the mast try spiral wrapping the upper spreaders with say an 6-8mm dia line, the aim again is to create a spiralling vortex breaker spotting the resonance.

Possibly the most famous example of this I know of in Australia is the Collin's Class Submarine with spiral wrap on the periscope to stop periscope vibrations from vortex shedding at speed. Same principle and it was a cheap and easy fix in the 90's.

Thanks; interesting. There have now been two nights of uncharacteristic glassy calm so might just live with it for the time I have left this trip.

Uncharacteristic very light northerlies predicted today (although not sure I believe it) so maybe not much sailing either.

Try this, I should have posted sooner, sorry.
Get whipping twine and wrap it around the shoud numerous times from top to bottom and pull it very tight and tie it off.
Problem solved, might have to play with the tension but you will get it right.

It is what we used to do when Kevlar and spectra first at came out and was replacing wire runners.
When loaded up they would sing constantly.

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lydia said..
Try this, I should have posted sooner, sorry.
Get whipping twine and wrap it around the shoud numerous times from top to bottom and pull it very tight and tie it off.
Problem solved, might have to play with the tension but you will get it right.

It is what we used to do when Kevlar and spectra first at came out and was replacing wire runners.
When loaded up they would sing constantly.

Thanks for that but I'm not quite sure how I would get high enough up. Do you think doing it to the bottom eight feet or so of the shroud would help? Also how many turns per foot would you be talking?
Wind was back with a vengance last night at about 2:00 a.m. after a couple of calm nights. Loud as hell again.

Try it as to turns go about one every 300 mm

That what I was trying to say, when talking about vortex shedding

So the noise begun once you replaced the shrouds with Dyneema?

Surely the mass per diameter would be vastly different. Under tension the Dyneema could possibly resonate at a much higher frequency than the heavier mass of the wire. It possibly also resonates, but at a pitch much lower so as not to be a problem. Can you change pitch by easing the tension on one or the other Dyneema shrouds?

DM

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ActionSportsWA said..
So the noise begun once you replaced the shrouds with Dyneema?

Surely the mass per diameter would be vastly different. Under tension the Dyneema could possibly resonate at a much higher frequency than the heavier mass of the wire. It possibly also resonates, but at a pitch much lower so as not to be a problem. Can you change pitch by easing the tension on one or the other Dyneema shrouds?

DM

Yes the vibration and noise suddenly started after I replaced the upper shrouds with dyneema. There was no noise before that.

I can't really retention the shrouds unless I am on the trailer and use the trailer winch to disconnect the forestay and so relieve tension on the shroud's whilst I mess with their tension.

The last couple of nights I actually resorted to putting a line between the shrouds and tensioning that line in order to pull them inboard towards each other and increase their tension. No luck it didn't relieve the din.

Anyway a solution will now have to wait for another day because my holiday is pretty much over and I just pulled the boat out of the water in prep for the long drive home.

Thank you everyone for the suggestions along the way most of which I tried but couldn't seem to make work.

So a few days ago I put the mast up on my trailer sailer on the trailer in my yard and have left it up whilst I do a few things.

Hell of a breeze today so I go out and put my ear to this shrouds and no hum whatsoever and none to be heard inside either. Was driving me nuts even in relatively light winds of say ten knots at night time on the water.

I guess the whole dynamics of the hull is different when it's sits on a trailer but if the problem originates with the shrouds I would expect it still to be there. Although it is damn windy in the yard it isn't a constant breeze like it is on the water and perhaps it needs to be constant to set up the resonance.

I haven't got the boom on either but I still find it strange. I must remember to sit the boom on the lifelines one night to relieve the the effect of the topping lift on the mast which is perhaps transferred to the shrouds if it happens again on the water.

Yes - Some clever fella will reveal the reason,once the boat is in the water,as the resonance may be multiplied/intensified by liquid ??

Definitely a wee breeze - just got out to mooring into 30knot Westerly,dodging the gusts behind stink boats - back ashore in an instant !

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Planter said..
Yes - Some clever fella will reveal the reason,once the boat is in the water,as the resonance may be multiplied/intensified by liquid ??

I am as intrigued as everyone else. I'm thinking more that the boat is acting like a violin or acoustic guitar - you have a tensioned wire or string that gets agitated (by bow, plectrum or wind) that is connected to a sound box (the hull and cabin) for amplification. The amplification in the water might be greater, because the hull is not supported on fixed points like it is on a trailer. The fixed points interfere with the resonance of the sound box, resulting in lower amplification and less noise. If this theory has any merit, it gives you two points of attack - taking the harmonics out of the wire as mentioned previously (try to anchor the wire at an irregular spacing that is not 1/2, 1/3, 1/4 or 1/8 of the length of the wire - if you have ever played a harmonic on a guitar string, you'll know why) and taking the harmonics out of the box, which is harder to do in the water. A grossly impractical approach for the latter is to fix a few props inside the cabin between the walls, hull and sole at an irregular pattern. They might fix the noise, but you will have to climb over them to get anywhere inside the cabin.

Just musing about how to stop your boat thinking that it is a guitar.

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Achernar said..

Planter said..
Yes - Some clever fella will reveal the reason,once the boat is in the water,as the resonance may be multiplied/intensified by liquid ??

I am as intrigued as everyone else. I'm thinking more that the boat is acting like a violin or acoustic guitar - you have a tensioned wire or string that gets agitated (by bow, plectrum or wind) that is connected to a sound box (the hull and cabin) for amplification. The amplification in the water might be greater, because the hull is not supported on fixed points like it is on a trailer. The fixed points interfere with the resonance of the sound box, resulting in lower amplification and less noise. If this theory has any merit, it gives you two points of attack - taking the harmonics out of the wire as mentioned previously (try to anchor the wire at an irregular spacing that is not 1/2, 1/3, 1/4 or 1/8 of the length of the wire - if you have ever played a harmonic on a guitar string, you'll know why) and taking the harmonics out of the box, which is harder to do in the water. A grossly impractical approach for the latter is to fix a few props inside the cabin between the walls, hull and sole at an irregular pattern. They might fix the noise, but you will have to climb over them to get anywhere inside the cabin.

Just musing about how to stop your boat thinking that it is a guitar.

Thank you. I am doing quite a few jobs on the boat ATM but when those are finished I'm re-tensioning the rig and putting a bit more pre-bend in the mast (a bit more like it was when I bought it which I thought was excessive) which will involve re tensioning the shrouds so that in itself may make a difference.

I also need to revisit whether it is one shroud or both making the noise as the main run of dyneema is different on each side by nearly 300mm due to a measurement error before splicing. The difference is taken up by additional length in the thinner dyneema lashing on the shorter side.

This boat won't be getting another outing till 1st October (school hols) so I'll report back on the riddle after that.

On the water the boat will be sitting head to wind normally, which could change things. My 28'er would start shaking the mast at a certain wind strength, almost certainly due to harmonic shedding, so I ended up using topping lifts and halyards to settle it down.

I'd look at hauling on the backstay next time the caps start singing, or dumping it, to reduce the shroud tension. Years ago there was an article in Oz Sailing that said that rig harmonics were a little-known problem that could cause major rig damage due to fatigue (IIRC) but I've only encountered them on my 28'er and they were so noticeable that they caused me to cure them. She also had stanchions that sang when going upwind in 15+ knots, but that was interesting rather than annoying.