Mast judder?

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squidge

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Hi we are suffering from a juddering mast . It happens when the breeze picks up a bit when not sailing, eg when trying to get some much needed kip. The shrouds are not slack when sailing and nore is the back stay , we also have a baby stay and its a mast head sloop rig. Any suggestions before i look at expensive rig tension setting thingies?

Thanks in advance.
 
Try wrapping a halyard several times around the mast from top to bottom and then secure it at the base. It breaks up the airflow around the mast - something to do with harmonics. I've seen it work a couple of times..
 
Its the topping lift our Beneteau does it .. Its the type of line used .. If you put a finger on it you can feel it humming .. Its a bit like a guitar string so .. We take the main haliard off the sail and secure it to the end of the boom .. Then pull it tight .. This takes the strain of the topping lift and away goes the noise .. /forums/images/graemlins/grin.gif .. Also keeps the boom up higher ..
 
>> Try wrapping a halyard several times around the mast from top to bottom and then secure it at the base. <<

How did they do that with all the rigging in place?

I too experience 'mast judder' occasionally and it's not the topping vibration or the forestay, it a much 'heavier' vibration altogether. It happens rarely and only for a couple of seconds at a time - at least on our boat - so we don't bother to anything about it.

I guess it's just a momentary alignment to the wind in a particulay way.
 
Quite easily. From masthead the halyard runs down to the spreaders then a few wraps spiraling down the mast inside the shrouds and then secured at the base of the mast.
 
[ QUOTE ]
>> Try wrapping a halyard several times around the mast from top to bottom and then secure it at the base. <<

How did they do that with all the rigging in place?

I too experience 'mast judder' occasionally and it's not the topping vibration or the forestay, it a much 'heavier' vibration altogether. It happens rarely and only for a couple of seconds at a time - at least on our boat - so we don't bother to anything about it.

I guess it's just a momentary alignment to the wind in a particulay way.

[/ QUOTE ]
Yes, I have never understood this advice. All you can do is wrap it round the lower part of the mast beneath the spreaders. It doesnt help.

The other advice is to hoist a sail bag or a fender on a halyard. The idea is that deflects the airflow enough to stop the effect. This also has its problems and the bag/fender are blown around if you cant get them very tight. On my boat I put two sail lugs in the track above those to which the mainsail is connected. I have used them to secure a fender so it stays close to the mast. I think it helps, but never been troubled enough when I have enough time to test it properley (rarely sleep on my boat).

On some boats it can be the tight topping lift. However on many it is the mast pumping. Once you feel the pumping you will know the difference between that and the humming topping lift.

Cause is "vortex shedding". Wikipedia explains more
Vortex-street-animation.gif
 
[ QUOTE ]
Quite easily. From masthead the halyard runs down to the spreaders then a few wraps spiraling down the mast inside the shrouds and then secured at the base of the mast.

[/ QUOTE ]
I think it depends where the spreaders are. On my boat they are quite low. To work you need to be able to influence the point of "max deflection". At least with my limited fender experiments then any benefit seems to be when the fender is about a foot or 2 above the spreaders.
 
In liveaboard marinas in the USA you quite often see this halyard wrapping practice. These people say it stops mast hum.
Simpler to try it than analyse it, I think.
 
[ QUOTE ]
In liveaboard marinas in the USA you quite often see this halyard wrapping practice. These people say it stops mast hum.
Simpler to try it than analyse it, I think.

[/ QUOTE ]
Yes definitely worth trying it. Every mast is different so it might hit the spot.

It didnt on mine so I moved on to "fender up the mast".
 
My old IOR used to suffer from this.It was a single spreader tall rig.I solved the problem by taking a genoa or spinnaker halyard down to a spreader root and from there to a point near the transom on the side opposite to the side of the mast the hallyard was run by.Then I tensioned it until the pumping stopped.I always left it in place when I left the boat.Mast pumping induces a lot of wear.
 
Ah, I see. It was the 'top to bottom' comment you made that puzzled me! Your suggestion is from the lower set of spreaders downwards. Never seen it done, but interesting that you confirm it works. /forums/images/graemlins/smile.gif
 
You get some funny effects if the topping lift resonates at a similar frequency to anything else, either tighter or slacker may cure it.
tuff luffs do the same, so many people run a little flag half way up, then sheet it firmly, breaking the resonating length in two.
The trouble is, being on deck will also change the resonance, so you will find it stops when you look at it!
 
Hi Wow that's great , many thanks to everyone who replied.

Its the mast pump rather than a topping lift hum (shudders the boat) i will work my way through the solutions and hopefully fine one that works.

I could and have sleep through the noise from the mast its the elbow in the ribs that wakes me up!
/forums/images/graemlins/smile.gif
Thanks again .
 
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