"Noisy" topping lift

DannyB

DannyB

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This may be familiar to some, but it's new to me. Walking down the pontoon towards the boat yesterday, I could hear a droning noise apparently coming from my boat. It came and went, reminiscent of that scene in Crocodile Dundee II where he climbs to the top of a cliff and whirls a bit of wood round his head on a string, as some kind of bush telegraph. I knew there could be nothing running on board, and when I climbed on, I could see the topping lift vibrating like a violin string, and the noise appeared to be coming out of the boom. When I put my hand on the topping lift, the vibration stopped along with the noise. It was absolutely flat calm at the time, not even enough wind to turn the indicator at the top of the mast, so what would cause the vibration? The line was under tension, it was carrying the weight of the boom, plus the main sheet was holding the boom central, but where did the energy come from to start the vibration? I'm assuming once it started there must have been some sympathetic resonance within the boom to sustain it. I've had the boat for six years and never heard this before.
 
Take the main halyard and wrap it around the topping lift 3 times before attaching to the end of the boom - job done.
 
Hahaha I've had my son looking for the cricket that lives in my boom ALL summer.. its actually a small vibrating ss sleeve on the topping lift shackle. Hours of fun :)
 
I recently changed my twin mainsheets from 2-part to 3-part (I'm getting feeble in my old age). I have used fiddle blocks to ensure a fair lead which means that the 3 parts of the falls are in line and when the wind is from ahead they set up an oscillation. Fortunately it doesn't make a noise though I haven't been aboard in a big blow yet.

I'm told owners of other Freewing masts have experienced howling from the sail track when the wind blows across it, to the extent of having to hoist a strip of cloth in the track to stop the noise. I have never had that.

I have to say that, having no standing rigging I never get that moan in the rigging that always knots the stomach when deciding whether to set out on a windy day.
 
I have cured this in various ways.
1/Tighten the mainsheet.
2/Slacken the mainsheet.
3/Tie the topping lift to the backstay as high as you can reach and then try 1 & 2 again.
4/ Tie a towel around the topping lift to dampen the vibration.
They all work a bit for some conditions but I've not found one that does all circumstances.
And then there is the standing rigging vibration, not found a fix for that yet!
 
Adonnante said:
Interesting that nobody has answered the question.

Peter.
Click to expand...
A good point.
I assume there must be some air movement, even a small amount will set up a resonant vibration.
Or perhaps it's picking up the very low frequency sound you sometimes hear on still days. e.g the Taos or Bristol hum.
 
Adonnante said:
Interesting that nobody has answered the question.

Peter.
Click to expand...

Yes, stopping it was easy, just a change in the topping lift tension, but it was one of those still days when smoke rises straight up from a chimney, no detectable air movement at all. I suppose it could have been windy earlier and a vibration became self sustaining, but doesn't that imply energy coming from somewhere else?

I'm glad to see I'm not the only one to have experience this.
 
Striking a resonance with whales humming, or a nearby submerged nuclear submarine?

On the other hand I heard this on my shallow water mooring on the river Exe a few weeks ago - I thought it might be something to do with the flat tape that a neighbouring boat had draped over it's rigging to scare the birds: it's meant to vibrate and drone in the wind and I wondered if it was transmitting through the water and causing my boat hull to resonate.
 
DannyB said:
Yes, stopping it was easy, just a change in the topping lift tension, but it was one of those still days when smoke rises straight up from a chimney, no detectable air movement at all. I suppose it could have been windy earlier and a vibration became self sustaining, but doesn't that imply energy coming from somewhere else?

I'm glad to see I'm not the only one to have experience this.
Click to expand...
I don't think perpetual motion exists, outside the world of superconductors anyway.

I get this problem because I like to tighten the mainsheet to keep the boom stationary since the gooseneck or boom strut tends to squeak with movement. I get over it by parking the main halyard at the boom end and letting it take the strain instead of the topping lift. The noise can be very hard to locate sometimes.
 
"but where did the energy come from to start the vibration?"

Well it can only be air movement or hull response to wave or current. A long topping lift will have a lot of possible harmonic modes of vibration and something is putting in energy at frequency close to one of those modes and my money would be on air movement. Interestingly the lower the windspeed the higher the frequency of vortex shedding. http://en.wikipedia.org/wiki/Vortex_shedding My flag halyards sometimes make a weird noise is pulled tight in quite light winds.
 
Doesn't anyone have boom gallows or crutches these days? My solution would be to drop the boom into the gallows and slacken the topping lift. No need for wrapping or tightening (or loosening) anything else.

Mike
 
Wooden Boat Fittings said:
Doesn't anyone have boom gallows or crutches these days?
Click to expand...

vangs.jpg
 
It's caused by wind of just the right strength coming from just the right angle to the boat. It sometimes stops within minutes if you swing the boat on a mooring.
 
Wooden Boat Fittings said:
Doesn't anyone have boom gallows or crutches these days? My solution would be to drop the boom into the gallows and slacken the topping lift. No need for wrapping or tightening (or loosening) anything else.

Mike
Click to expand...

I've got a strut which supports the boom, but when the topping lift is slack the boom just touches the top of the sprayhood, so I tend to leave a bit of tension on the topping lift. It's never caused this noise before, probably a million to one coincidence of topping lift tension and a momentary breeze. I'm reassured that other people have experienced it too, but I can't get over the volume of noise, and lack of wind, I have to assume the boom was acting like a resonant sound box.
I always secure my main halyard to a loop of cord on top of my main sail cover about halfway along the boom. This stops it clattering against the mast, and saves me clambering about to get it to the end of the boom.
Knowing my luck, if I wrapped the halyard round the topping lift, I'd probably forget until the next time I tried to hoist the sail and get myself in a tangle.
 
I experienced this this the other week. I had gone on the scrubbing posts overnight for an early start. The noise from the Dredger discharging kept me from my usual level of beauty sleep. Several times through the night it felt like the whole boat was vibrating along with an eastern mystic meditating. Strange.
 
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