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Old 12-01-2014, 09:37   #1
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Boat Shudders With High Wind Gusts

Moon Dance has all new standing and running rigging. I used a rigging tuner made by a company called Loos and Company to adjust the 9/32 wire to their recommended specifications, 1500lbs for the headstay and 1000lbs for the rest of the shrouds. If I get high gusts of wind when the boat is in the slip the boat starts to shudder and its funny because it starts from the keelson on up to the rigging as the speed of the gust climbs, usually around 28mph and above.

It has been suggested to me that a sailboat's rigging is like the strings of a guitar and at a certain wind speed a harmonic vibration starts and that is what I am experiencing. Wondering what the members feel about this.
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Old 12-01-2014, 09:54   #2
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Re: Boat Shudders With High Wind Gusts

Cutter rig or sloop? How many spreaders? Height of mast?

My 50 foot tall, two-spreader cutter positioned mast does not have the staysail or running backstays rigged. It will develop a resonant vibration when winds get about that speed. If I rig the running backs and staysail, which attach near the upper spreaders, the mast is "tuned" such that the winds would have to get a heck of a lot stronger at the dock to make it vibrate the mast. The rigging wires (shrouds and stays), however, have their own resonant frequencies, and "whistles". Then, there are my neighbors whose roller furler foils rattle in even the lightest winds, which would drive me absolutely nuts if I had that rig.
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Old 12-01-2014, 09:54   #3
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Re: Boat Shudders With High Wind Gusts

Grab a lower and shake it hard , see if the mast pump more than usual, mine start at 20 or 25 knts, is kinda a rumbling and some mast vibration,if the mast is keel steped could be some gaps in the mast deck collar , but anyway is very normal, forestay tight , some wobling and a light banana shape under sail is ok, backstay, just until the mast start to get a rake aft not to tight not to loose, uppers tight, if you have a couple of lowers dont tension the fwd lowers to much, tight instead the iner forestay for the staysail and compensate with the aft lowers, i guess the iner forestay got a runing back wires atached to the lowers chainplate? the best way is sailing in a breeze in both tacks and check that the mast is straight ...
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Old 12-01-2014, 10:09   #4
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pirate Re: Boat Shudders With High Wind Gusts

I'd say your over tensioned somewhere.. but then I tension by eye and touch on my boats.. many feel/think I don't tension enough but never lost a mast or had a shudder on my boats.. though a Carter 30 did when I first got it..
But.. I'm no expert..
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Old 12-01-2014, 10:32   #5
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Re: Boat Shudders With High Wind Gusts

In many cases it's related to mast pumping: Home Page Brochures* Contribute Cool stuff Database FAQ Fleets For sale* Gallery** History JOIN Links Mailing List Manuals Message
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Old 12-01-2014, 11:10   #6
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Re: Boat Shudders With High Wind Gusts

Mast is 50' deck stepped with a single spreader, cutter rigged, running backs are not setup whilst in slip. I followed the factories specs for tuning however was no mention of using the tuner. Boat does not exhibit this issue under sail and sails beautifully.
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Old 12-01-2014, 15:21   #7
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Re: Boat Shudders With High Wind Gusts

[QUOTE=boatman61;14383.. but then I tension by eye and touch on my boats..


A yard rigger once told me that a properly tuned rig reduced stresses to both rigging and boat, suggesting tighter was better then more slack. I have a ketch and recently tuned all wires but haven't noticed any change in the shuddering, I also have. It seems to diminish depending on wind direction change at dockside and feel it less or reduced when underway.
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Old 12-01-2014, 15:28   #8
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Re: Boat Shudders With High Wind Gusts

Quote:
Originally Posted by Salty Skipper View Post


A yard rigger once told me that a properly tuned rig reduced stresses to both rigging and boat, suggesting tighter was better then more slack.
I've heard the same & it's definitely the way to go. I actually paid a rigger to tune mine one year, but still had the problem. The only cure was to go tight on the forward lowers... & I mean crazy tight.

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Old 12-01-2014, 15:48   #9
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Re: Boat Shudders With High Wind Gusts

I have the boat tuned well, went out before and set up the runners will she if that reduces the vibration some peace knowing this happens to others boats.
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Old 12-01-2014, 17:41   #10
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Re: Boat Shudders With High Wind Gusts

It may be Harmonic Resonance.

This little trick of science has bugged architects and engineers for thousands of years. In fact it totally pissed off the romans when they were building bridges because when long lines of troops marched over them the harmonic Resonance could cause the bridge to fall down!

All engineers will see a film in their first year at university showing a bridge in the USA turning into a fluttering ribbon in quite low winds, maybe 40 knots, till it ripped itself apart.

Another new bridge that had it is the ANZAC bridge in Sydney over a portion of Sydney Harbour. It started to resonate along its stay wires when there was NO wind! It happened when a very light drizzle would fall.

But their solution could be your solution. They tied short ropes from part way up the stays to the road way. Problem solved.
So experiemnt with a bit of rope from your shrouds to a toe rail at 90 degrees and see what happens. It doesnt need to be strained, just enough to change the resonance.


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Old 12-01-2014, 18:11   #11
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Re: Boat Shudders With High Wind Gusts

My boat, a Lagoon 410 will get these vibrations also. It never happens at anchor, only at the dock. The vibrations will shake the whole boat. I narrowed down what was happening to the fact that under certain wind directions and velocities the mast will create a vortice on the downwind side. I solved the problem by hauling up a fender about 3/4 the way up the mast using the spinnaker halyard. The fender disrupts the formation of the vortice and thus the vibration. It doesn't happen all that often, so hauling the fender up hasn't been a hassle.
Next time you see a tall smoke stack or other similar object take a look. It will have some sort of spiral bands going up the stack to break up the vortices. Try the fender idea and see if it works for you...Sid
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Old 12-01-2014, 18:19   #12
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Re: Boat Shudders With High Wind Gusts

Quote:
Originally Posted by cburger View Post
Mast is 50' deck stepped with a single spreader, cutter rigged, running backs are not setup whilst in slip. I followed the factories specs for tuning however was no mention of using the tuner. Boat does not exhibit this issue under sail and sails beautifully.
Yes, the issues exhibited in my prior link discuss only mast pumping (and other bangs in the night) when tied up or anchored. When sailing, I have had no reports of this occurring (in 35 years at it).
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Old 12-01-2014, 18:51   #13
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Re: Boat Shudders With High Wind Gusts

If it has double lower shrouds I vote for mast pumping, though I've been calling it mast panting.

Slope with a masthead rig on my Pearson, and the issue with the mast base common to this model caused my rig to be loose when I bought the boat. I tuned it with a Loos gauge also. With the forward lowers tightened a bit more than the rear the panting went away.

Now, two years later with the rig loose again from the mast issue, the panting is coming back. No more room on the turnbuckles so it's time to finish the mast base repair.

Tighten the foward lowers some, might help, won't hurt.
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Old 13-01-2014, 06:37   #14
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Re: Boat Shudders With High Wind Gusts

Quote:
Originally Posted by Sid at SailAway View Post
My boat, a Lagoon 410 will get these vibrations also. It never happens at anchor, only at the dock. The vibrations will shake the whole boat. I narrowed down what was happening to the fact that under certain wind directions and velocities the mast will create a vortice on the downwind side. I solved the problem by hauling up a fender about 3/4 the way up the mast using the spinnaker halyard. The fender disrupts the formation of the vortice and thus the vibration. It doesn't happen all that often, so hauling the fender up hasn't been a hassle.
Next time you see a tall smoke stack or other similar object take a look. It will have some sort of spiral bands going up the stack to break up the vortices. Try the fender idea and see if it works for you...Sid
I will give it a go
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Old 13-01-2014, 06:55   #15
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Re: Boat Shudders With High Wind Gusts

Well, here I thought Night Watch imitating a black drum in mating season was unique! Winds sometimes create a deep, booming bass vibration that rumbles the whole world. My rig is waaay loose, though, and it still happens. I believe it's when the wind aligns with the fore-aft axis of the mast. I'm going to try the fender trick. Easier than wrapping the halyards.

I'm dropping the tabernacle mast in the next couple of weeks (haven't done that evolution yet), then tightening and tuning. I have forward and aft lowers, forward ones "break away" to allow mast to lie back when roller furling is cast loose. I expect this to be fussy!
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