Mast pumping?

[Travelling Westerly]

You'll have to excuse me if I have the term wrong but it seems to fit the issue I'm having at present and extensive googling came up with "mast pumping".
Basically just had a recent rig tune and inspection, all OK, but during windy evenings the mast and rigging seems to pump which is then transfered down to the aft cabin and my bed! Now I can see where some responses/replies may go but keeping it fairly clean does anybody know how I can stop it? I don't remember this happening before the tune up but my memory may be failing me.

Thanks

 

[Habebty]

Common issue. It is more likely to be your topping lift or main halyard if it is shackled to the end of the boom. Just ease the tension and the resonant frequency will disappear.

 

[NotBirdseye]

Put some extra cushioning underneath would be my first thought. You may also want to add some extra padding around the deck hole, make it as tight fitting as possible... wow this is a really hard subject not to make dirty...

 

[Quandary]

If you tell us a little more about your rig it might be easier to help. Deck or keel stepped, fractional or masthead, swept spreaders, fixed or adjustable backstay, how much prebend that sort of thing. I tend to associate the term 'pumping' with inversion of the mast bend but I suspect this does not go as far as that?

What did your rigger say it was?

 

[anoccasionalyachtsman]

Pumping generally means that the body of the mast is responding to the accelerations and decelerations that it's experiencing - it bends a bit forwards and a bit backwards (or a bit less forwards if it's pre-bent).

What you've got is the mast responding to vortex shedding - it's what makes halyards rattle, shrouds hum etc.. and it will happen to most masts. Unfortunately for you, the resonant frequency of your mast has been changed to that where the wind can have its fun. If you find it affecting you personality you could steal a trick from the more up market flag makers who sew a band of netting down the trailing edge - hoist a strip up the luff groove to collapse the vortices. It'd need to be a couple of mast diameters wide so that it can work in all directions.

Edit. I'll add a bit. All the rigging has resonant frequencies, and it can also be that they act in concert (stringed instruments obviously) and set the mast going. That tends to be the odd shudder every now and then. There was a great video of 'Yacht A' and its wing mast whipping around, but I can't find it - dunno if anyone else can?

 

[scrambledegg]

ok, this is most like caused by "vortex shedding" (look up on wikipedia) of the mast. It is a common problem of bluff structures such as chimney stacks which is why they sometimes have a spiral web around the outside from top to bottom. to disrupt the airflow in the right way. You get the vibration when the frequency of vortex shedding matches the resonant frequency of the mast structure.
I'm guessing your recent rig tune has changed your mast's resonant frequency and exacerbated the problem.
What to do about it I don't know.
(ok crossed messages with the previous post)

 

[Travelling Westerly]

If you tell us a little more about your rig it might be easier to help. Deck or keel stepped, fractional or masthead, swept spreaders, fixed or adjustable backstay, how much prebend that sort of thing. I tend to associate the term 'pumping' with inversion of the mast bend but I suspect this does not go as far as that?

What did your rigger say it was?

Its an inmast Selden set up, mast head, twin spreaders but not swept back at all. The back stay splits into 2 sections and both have turn buckles so adjustable I guess. There is a baby stay as well.
The mast had prebend in but the new riggers said it should not have any as its an inmast unit. It was after their tune up that it started pumping - alot! I've written an email to them so awaiting their reply.
One thing I did seem to find on Google was others who had the same issue suggested the rig was to tight. If I took half a turn off each turn buckle on the whole rig would that be a safety issue?

 

[RupertW]

I agree with those who say it’s most likely to be the topping lift humming and feeding down through the mast. If any halyard is under tension it could be that. So if you have a solid vang ease off the topping lift and ease off the vang - and of course don’t have the main sheet tight either as that will also tension the topping lift. Then to avoid the boom banging backwards and forwards tie off the boom end of the main sheet to a side cleat.

Then you can go to bed and discover what the next noise is.

 

[pvb]

Its an inmast Selden set up, mast head, twin spreaders but not swept back at all. The back stay splits into 2 sections and both have turn buckles so adjustable I guess. There is a baby stay as well.
The mast had prebend in but the new riggers said it should not have any as its an inmast unit. It was after their tune up that it started pumping - alot! I've written an email to them so awaiting their reply.
One thing I did seem to find on Google was others who had the same issue suggested the rig was to tight. If I took half a turn off each turn buckle on the whole rig would that be a safety issue?

I had a problem with mast pumping on a previous boat. In the end, I was supplied with a flexible plastic strip, about 100mm wide, which could be hoisted in the spare luff groove of the mast, and which stopped the problem. It is indeed a vortex problem. I'm not sure that fiddling with halyard or topping lift tensions will help.

 

[vyv_cox]

It is not the topping lift. My mast pumps with the boom in the saloon for winter! As said it is vortex shedding but the phenomenon is increased by static rig tension. Applying compression to the masthead makes the mast deflect more easily. Loosening it a little could help but not at the expense of shroud fatigue failure.

 

[Hydrozoan]

Is there accepted and common terminology here? I had thought ‘mast pumping’ to be an undesired fore-and-aft movement of the middle section of the mast particularly when sailing, and had attributed vibration and noise of the kind described by the OP (which I can get when the wind is in a particular direction on the berth) to be a resonance phenomenon (sometimes involving interaction of mast and boom etc. as described by RupertW at #8) and that ‘vortex shedding’ was a cause of the latter.

 

[anoccasionalyachtsman]

Is there accepted and common terminology here? I had thought ‘mast pumping’ to be an undesired fore-and-aft movement of the middle section of the mast particularly when sailing, and had attributed vibration and noise of the kind described by the OP (which I can get when the wind is in a particular direction on the berth) to be a resonance phenomenon (sometimes involving interaction of mast and boom etc. as described by RupertW at #8) and that ‘vortex shedding’ was a cause of the latter.

I'm not going to stoop to quoting post numbers, but yes, I agree with your description!

 

[Travelling Westerly]

It is not the topping lift. My mast pumps with the boom in the saloon for winter! As said it is vortex shedding but the phenomenon is increased by static rig tension. Applying compression to the masthead makes the mast deflect more easily. Loosening it a little could help but not at the expense of shroud fatigue failure.

This makes sense to me Vyv, thanks. Is my rationale correct that if I take half a turn or a full turn off all turn buckles then the mast will remain in the same position but the rig tension will decrease? Shroud fatigue I'm not sure about so I'll read up on to understand.

Thanks again

 

[Hydrozoan]

I'm not going to stoop to quoting post numbers, but yes, I agree with your description!

My citing one post - and not your earlier and more detailed answer - was because its simple description was what I had understood to be the phenomenon in question (as opposed to 'mast pumping' as I described it) before I had ever heard of vortex shedding.

Apologies for any unintended slight, and thanks for the reassurance of your agreement: the 'pumping' description seemed to me to risk ambiguity. But so as not to offend the OP or anybody else, I'd better add that the rhythmic nature is indeed a kind of 'pumping' - it's just that I thought the other kind had got there first, terminologically-speaking.

 

[vyv_cox]

This makes sense to me Vyv, thanks. Is my rationale correct that if I take half a turn or a full turn off all turn buckles then the mast will remain in the same position but the rig tension will decrease? Shroud fatigue I'm not sure about so I'll read up on to understand.

Thanks again

I think that would work but of course might not be the best setup for sailing.

 

[RJJ]

Its an inmast Selden set up, mast head, twin spreaders but not swept back at all. The back stay splits into 2 sections and both have turn buckles so adjustable I guess. There is a baby stay as well.
The mast had prebend in but the new riggers said it should not have any as its an inmast unit. It was after their tune up that it started pumping - alot! I've written an email to them so awaiting their reply.
One thing I did seem to find on Google was others who had the same issue suggested the rig was to tight. If I took half a turn off each turn buckle on the whole rig would that be a safety issue?

Selden publish a comprehensive rigging guide that tells you how to adjust your rig tension, with specific sections for each type of rig. I'd refer to that; if you use the folding rule then you can see the impact of half turn, and also see what your riggers did.

I wonder if pulling on the babystay would settle it down?

 

[anoccasionalyachtsman]

My citing one post - and not your earlier and more detailed answer - was because its simple description was what I had understood to be the phenomenon in question (as opposed to 'mast pumping' as I described it) before I had ever heard of vortex shedding.

Apologies for any unintended slight, and thanks for the reassurance of your agreement: the 'pumping' description seemed to me to risk ambiguity. But so as not to offend the OP or anybody else, I'd better add that the rhythmic nature is indeed a kind of 'pumping' - it's just that I thought the other kind had got there first, terminologically-speaking.

Ah, I can see what you might have thought! Not intended - I was just avoiding a certain posting style...

 

[anoccasionalyachtsman]

Selden publish a comprehensive rigging guide that tells you how to adjust your rig tension, with specific sections for each type of rig. I'd refer to that; if you use the folding rule then you can see the impact of half turn, and also see what your riggers did.

I wonder if pulling on the babystay would settle it down?

Yes - I meant to suggest the babystay as a quick fix.

 

[Travelling Westerly]

Selden publish a comprehensive rigging guide that tells you how to adjust your rig tension, with specific sections for each type of rig. I'd refer to that; if you use the folding rule then you can see the impact of half turn, and also see what your riggers did.

I wonder if pulling on the babystay would settle it down?

Ive just printed that guide out so got some bedtime reading ahead. I heard the rigger say to his mate that he didnt want to tension the baby stay any further so not sure I want to try that as I'm no expert here. Good call though

 

[vyv_cox]

Yes - I meant to suggest the babystay as a quick fix.

I have spent quite a long time playing with babystay tension to try to overcome the problem. Unfortunately unsuccessfully. With forward bow of about half the mast fore and aft thickness, 2-3 inches, the pumping quite regularly exceeds this figure. Any more bow than that is too much for the mainsail.

I wind halyards in a spiral below the spreaders but this does not make a huge improvement.