Mast Pumping / Vibrating

[Ocean Girl]

Ralph, I was riding that out little storm too I love that kind of weather, but only waay offshore or snug in a slip, not in between. I moved from watergate's old piers to waterford nice strong piers which makes riding out those blows more enjoyable, cause I trust em.

I think you guys are right about the rig being too tight. Can someone explain why a tight rig will cause pumping. If I can visualize what is happening then I think I can figure out where I am going wrong. Truly, the rig looks nice and straight with a small rake 3/4 of the way up.

BTW- all day the winds have been 20-30 knots from the southeast, straight off my bow. A northern just hit with even higher gusts and no pumping of the mast. So would that say bow too tight? I'll play with it, just thought it was an interesting observation. I have owned 6 sailboats and never had this problem with tuning my rig, maybe I am losing my touch...

Thanks again everyone, and as usual, you all are a great help,
Erika

[rebel heart]

This is when it's nice to have a wood spar. No creepy harmonics other than wind whistling through.

[Ocean Girl]

Rub it in Rebel Heart, rub it in. But I was a varnish lady before becoming a nurse so I know what it takes to keep a wooden mast maintained. I'll sit and listen to my metal hum while your up the mast varnishing
Cheers,
Erika

[rebel heart]

I went the epoxy / paint route, but don't worry I don't ride much of a high horse with it up there. I'm happy with it, and have had it checked out by a lot of people and re-rigged, but if I could wave a wand and switch out to aluminum I'd be happy to do so.

The varnish seems easy until you finish up and find little splotches and whisps of varnish all over the cabin top and decks. Drips from 50' in the air end up everywhere. No fun!

[JiffyLube]

For what it's worth the PO of our boat told me he had a problem with mast pumping, but I've never experienced that since I've owned the boat for 3 years now...at least that I know of. His solution was to run the extra halyard down to an attachment point on the bow (no bow sprint on this boat), but I've never done it to see what that was suppose to do. After we bought the boat from the PO I had a rigger tune the rigging, but I never asked if the rigging needed tuning...so I don't know if that solved the problem the PO had been experiencing.

[bewitched]

Originally Posted by Ocean Girl

Can someone explain why a tight rig will cause pumping.

Harmonics was mentioned earlier - this is the reason.

As wind hits your circular rigging, it needs to go arround this obsticle. But it doesn't do so in an even fashion - it whips round one side and then the other and the rigging starts to oscillate. At a certain windspeed this oscillation becomes regular (and the rigging 'sings"). The rigging, because it is long and thin amplifies this oscillation and the movement is transferred to the mast.

The tighter the rigging, the more prone it is to oscillation.

[s/v Jedi]

I do not agree with the pumping mast as a result of something too tight.

Vibrations, sounds etc. are okay, but not the mast pumping, that's a whole different thing. I expect that a problem with the rigging will be found. Most often, there's something wrong with fore & back stays with the cutter and/or baby stay high on the list. A sagging compression post is a good candidate too.

But it isn't clear to me that there was a visual confirmation of the mast actually pumping. I remember one time that we took the jib down and the empty furler-profile interacted with the wind causing wild vibrations that could easily be confused with a pumping mast. The solution was to turn the profile with the slot for the sails facing away from the wind and lashing in that position (or keep the jib up).

The only time our main mast was pumping was when the seals in the hydraulic tensioner for the cutter stay failed. The mast must have a positive bend to prevent pumping for every modern design.

cheers,
Nick.

[Cheechako]

I'm trying to remember my masts that pumped...... it seems to me the ones that pumped had some bend in them at anchor..? (top aft of course) I guess that could indicate tighter rigs are a problem as mentioned above ... or just the effect of having that prebend in the "column" allows it to cycle as opposed to a stable and straight column....?
Watch riggers though, they are used to adjusting for racing, and that means tight. I always did the final adjustment on mine while the boat was sailing. I want the mast to stay straight athwartships and the lee stays and shrouds to loosen up just a little (I mean like actually go slack) in a good blow to weather. Also watch for the top of the mast to not go forward... you want the mast to stay fairly straight although some forward bend in the middle may be necessary.... flattens the main...

[Tom Spohn]

Adjust backstay and checkstays (or running backs) if you have them.

[s/v Jedi]

I looked into this a bit more and think that the lack of a cutter/baby stay, or one that isn't tensioned enough is the cause. If the pumping stops while under sail, there's tests that can be done while moored. A temporary cutter stay can be rigged for testing too.

cheers,
Nick.

[barnakiel]

Sometimes a too fine extrusion will vibrate when overcompressed. Try less tension in the rig.

b.

[lancelot9898]

The mast pumping reminded me of what happened last winter during an ice storm with all sails stored for the winter. There the boat sat in the water with 20 plus knots of wind and the roller furler foil hitting some sort of harmonic frequency. I've never seen that before in the 20 plus years of owning the boat plus having been aboard during a Cat 1 hurricane and numerious storms and gales. I solved the immediate problem by putting a line on the furler foil and thus changing the damping. This past spring I then put more tension in the headstay too. I've always tuned the boat by the "folding rule method" but have never been able to figure out how to judge the tension in the headstay since the foil is attached. This coming winter when removing the sails, I'll probably leave a line attached to the foil because the harmonics that I saw was not pretty!

[Jmolan]

I learned this from Brion Toss. You can check with him or his forum also.

Mast vibration at the dock is harmonics where the wind is building up on one side of the mast and creating vacuums on the other side (or something like that)

Try to notice if the wind is from the same direction when you get the vibration. Flip the boat around in the berth, or hoist a fat rope or even a fender (I kid you not) up the leeward (vacuum) side. It will break up the vortex. Or get another berth.

Mast vibration while sailing is another thing and needs tuning attention. All this according to Brion.

[Jmolan]

Originally Posted by Ocean Girl

Ralph, I was riding that out little storm too I love that kind of weather, but only waay offshore or snug in a slip, not in between. I moved from watergate's old piers to waterford nice strong piers which makes riding out those blows more enjoyable, cause I trust em.

I think you guys are right about the rig being too tight. Can someone explain why a tight rig will cause pumping. If I can visualize what is happening then I think I can figure out where I am going wrong. Truly, the rig looks nice and straight with a small rake 3/4 of the way up.

BTW- all day the winds have been 20-30 knots from the southeast, straight off my bow. A northern just hit with even higher gusts and no pumping of the mast. So would that say bow too tight? I'll play with it, just thought it was an interesting observation. I have owned 6 sailboats and never had this problem with tuning my rig, maybe I am losing my touch...

Thanks again everyone, and as usual, you all are a great help,
Erika

There ya go!

[Jmolan]

I found this just now.



Mast Vibration

Sleepless Nights!

Anyone who has a vibrating mast knows how much of a nuisance this can be when trying to sleep or otherwise spend time down below. Mast vibration causes a great deal of noise below decks since the hull acts like a sounding board and amplifies the vibration noise.

Vibration is more likely to occur on poorly stayed deck stepped masts, usually with single lower stays which do not provide fore/aft support. Technical Explanation

The technical explanation of mast vibration is something called Karman vortex shedding. Basically, air flowing over the mast does not re-attach as it would over an airfoil and this causes regions of low pressure on the leeward side. These regions are unstable and tend to move up and down as the vortex shedding occurs. The rate at which the low pressure regions move is a function of windspeed, mast diameter and shape. When the natural frequency of the mast section coincides with the frequency of the vortex shedding, a resonance can occur which results in an marked increase in amplitude and severe vibration can occur. This phenomenon often occurs at quite low windspeeds (4-12) knots.

Vortex shedding is common on tall slender chimneys - If you look at any industrial plant, you will likely see a chimney with spirals welded on. These spirals are intended to move the low pressure regions from the leeward side to the windward side and thus overcome the vertical movement of the eddies. Quite a lot is known about Karman vortices, but this has not always been useful in yacht design. Solutions?

At the design stage, the designer should consider the following:

1. Mast Support - Keel vs Deck or at least ensure the mast step is well supported.
2. Mast staying - Use fore/aft lowers or swept back spreaders to better provide fore/aft staying
3. Mast Section - Analyse the mast natural frequency vs Karman vortex shedding.
4. Mast Shape - It could be that some mast shapes are better than others.

Once you have this problem, there are a few things that could be tried:

1. Mast Step 1 - Ensure that the mast base is fully supported on the mast step and not bearing on a point.
2. Mast Step 2 - Ensure that there is adequate support under the mast step - there is sometimes a gap.
3. Rig Tension 1 - If you have fore/aft lowers or a baby stay, try varying the tension.
4. Rig Tension 2 - Try adjusting upper shroud tension - This affects the natural frequency of the mast.
5. Temporary support - Tie a line from the Jib tack to the spinnaker eye or simply around the mast.
6. New Stays - add fore/aft support by adding baby stay or additional lowers.
7. Add a Vortex Fence - A narrow stiff (2 to 4") strip raised to say 2/3 of the mast height in the mast slot.
8. Try using your mainsheet to tension the topping lift and provide some forward boom force to stiffen the lower mast.
9. Try inducing some mast bend with the backstay adjuster - this will stiffen the mast.

Summary

This an annoying and difficult problem to solve - There is no simple answer. The only way is to keep trying ideas until something works for you. Good Luck!