Pumping mast!

[delmarrey]

Originally Posted by mitiempo

Rigging ages at the dock or in use. The stress of use will add to this but the corrosion in the swages exists regardless.

In response to another thread but something to ponder.

Had a odd situation today at the boat. While up forward below decks I could hear the occasional chafing of a snap shackle on a padeye. It came in a sequence of about 1 minute on/off.
I went up on deck and looked around and found that my 60' aluminum extrusion (mast) was pumping off & on, in a 7 kt breeze. The boat's on the hard and I've never seen it do this before. The wind must have been coming from just the right direction at the right speed. It makes me want to install running back stays for bare poles.
Anyway, I tightened up the spinnaker boom topping lift to a forward padeye and it stopped the pumping.
SOooo, rigging can get wear just sitting around!

[Nemo55]

A little help for the uninitiated,,,,what is a pumping mast?? Thanks :-)

Originally Posted by delmarrey

In response to another thread but something to ponder.

Had a odd situation today at the boat. While up forward below decks I could hear the occasional chafing of a snap shackle on a padeye. It came in a sequence of about 1 minute on/off.
I went up on deck and looked around and found that my 60' aluminum extrusion (mast) was pumping off & on, in a 7 kt breeze. The boat's on the hard and I've never seen it do this before. The wind must have been coming from just the right direction at the right speed. It makes me want to install running back stays for bare poles.
Anyway, I tightened up the spinnaker boom topping lift to a forward padeye and it stopped the pumping.
SOooo, rigging can get wear just sitting around!

[Target9000]

Originally Posted by Nemo55

A little help for the uninitiated,,,,what is a pumping mast?? Thanks :-)

While at the dock it is usually a harmonic oscillation caused by fluctuating vortexes of air passing the mast.



Under sail is a different matter. Running backstays can be rigged to deal with this under sail. At the dock I've heard of people hoisting fenders to disrupt the air flow around the mast.

[Nemo55]

You mean like a reed oscillation on a harmonica?? which would make noise like a heavy bow????

[delmarrey]

Originally Posted by Target9000

At the dock I've heard of people hoisting fenders to disrupt the air flow around the mast.

That reminds me. I heard that if you wrap a halyard spiral around the mast that helps too.
As for the pumping the mast was oscillating fore and aft about 2-3" just below the top spreaders but no noise, just vibration.

[Nemo55]

Ok,,Got it!!
Terms i can understand.

Originally Posted by delmarrey

That reminds me. I heard that if you wrap a halyard spiral around the mast that helps too.
As for the pumping the mast was oscillating fore and aft about 2-3" just below the top spreaders but no noise, just vibration.

[44'cruisingcat]

I saw a 70 metre tall by about 5 metre diameter propane/propylene splitter column on a refinery pumping in about a 15 knot breeze. It was still under construction, so the feed and reflux lines hadn't been installed yet. Pretty impressive though.

[matauwhi]

Originally Posted by 44'cruisingcat

It was still under construction, so the feed and reflux lines hadn't been installed yet.

G'day, mate. Sounds like chemical engineering speak there! Yup, if the mast starts pumping, time to put on the running back stay, around when the apparent wind speed starts to creep over 20 kts to windward for us. Cheers.

[DumnMad]

My furled headsail was doing that in 10 to 15 knots, like you I felt this oscillation vibrating the whole boat. Just pulled on it a bit and it stopped and it never started again.

[ozskipper]

Sounds like a harmonic to me also. You may get a similar minimization using the boom and vang to adjust the shape of the mast somewhat and its ability to pump -even back stay if its a 3/4 rig. Though i kinda like your topping lift solution better.

Runners and Check stays and their entire family belong in the 80s in my opinion. They way over complicate a cruising rig.

[GordMay]

Mast pumping is common, but abnormal.

- Objectionable mast pumping, AT THE DOCK, can often be ameliorated by twisting together, then wrapping the twisted halyards around the mast, and hauling them very tight.
This disrupts the formation of the Von Karman vortices, that cause the harmonic oscillations.
- Another easy way to do this is to run a small fender up a main halyard, with a line attached on other end, so it can held tight.
- You could also move to a dock, oriented at 90 degrees to your present berth, changing the mast foil orientation to the prevailing winds (probably not very practical).
- Changing the tension of the shrouds (rig tuning) will also change the resonant frequency, but may have other unintended deleterious consequences.

[Tingum]

Chances are that the boat has flexed slightly from uneven blocking on shore. I would be concerned if this was happening while in the water. Don't attempt to adjust anything while hauled out as the boat is not taking its true shape.

[Samantha ann]

I found just putting a bungie on my lowers stopped it

[Jetexas]

Mine has been doing this at the dock from time to time ever since the wind changed in the spring and started coming out of the south. Shakes the entire boat.

I've tried loosening/tightening the backstay tensioner with no real change. I'll try the fender trick.

[Blue Stocking]

Muss be dese new-fangled alooium masts that think they are pipe organ rejects.
My 48 feet of Douglas fir sits really still.
--but dont let a halyard get loose--all hell breaks out.