Rig pumping at the dock

[Rocket_Science]

I'm hoping someone here might have had a similar problem and have some suggestions. The rig on my boat pumps badly while at the dock with the wind on the beam. Here in FL we frequently get strong easterlies overnight and as I am a liveaboard and my slip faces N/S it can be very annoying. I have had the rig tuned by the local (and very good) riggers which didn't really help at all. I'm planning to ask them again about it anyway.

The boat is a Tartan 3800 - masthead rig, double spreaders with inline lowers and a babystay. I do have an adjustable backstay. The rig does not pump while sailing, just at the dock!

Suggestions/tricks besides just cranking more on the babystay and backstay??

[JoeRobertJr]

This thread has some interesting information on mast pumping and some countermeasures.
https://www.cruisersforum.com/forums...ast-80431.html

[GordMay]

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.

[Rocket_Science]

Thank you, very helpful suggestions! My concern with wrapping halyards around the mast is that I would only be able to wrap below the lower spreaders - not sure how much help that would be and would leave the rest of the halyard free to bang around. Has anyone actually done this? I'm thinking I will try the fender trick.

[tkeithlu]

I guess boat designers are not up on harmonics as applied to the length of the mast. Pursuing harmonics has been basic engineering every since Liberty ships and Comet jet air liners started coming apart in the 1950s.

Anything that you can do to change the harmonic frequency of your mast is likely to work. Straping a weight to it, leaning the dinghy against it, tying a taut line from half way between the nodes (Look up it when it's pumping) to the hull; be creative in your frustration. Then, sit down in the cockpit with a really good gin and tonic and listen to other people's boats vibrate.

Playing with the shrouds will change the harmonic frequency; you are tuning a violin string, but it may not alter it enough to stop the pumping. You might get enough by tying the lower shrouds to the mast. Tightly, between the nodes. Your spreaders may define the nodes, like the bridge on a violin.

[Sailmonkey]

Our mizzen pumps a lot unless I cross the halyards on the leadingI edge of the mast. It’s not much but it doesn’t take much to disturb the vortices.

[Cheechako]

A topping lift or staysail halyard can be used to stop the pumping, But you cant just attach it, you have to have a stopper knot or etc at the block, or wrap around the mast below the block, or the line just rolls/pumps through the block. yeah it's annoying as heck!

[Michael Pope]

The previous helper was correct it is caused by the karmen shed!

You can make fairly radical changes in the Mast's natural frequency by loading the mast. Pick your choice: No 1 detach the Baby stay ( the shortest life stay on the boat for just this reason ) when not sailing. Then use the Spi pole topping lift or a staysail Halyard or both under tension and preferably with a textile (rope) fairly long link in it to Damp the vibration ( the rope will stretch so needs periodic tensioning) . Tension the backstay to induce some Mast bend ( as long as it is a metalmast it will do it no harm it will not creep ,
but a Carbon Mast just might. Make a banner out of heavy sail cloth that feeds into your Luff groove (if you gave one) and sheet it to the end of the boom. If that does not work take the Banner and add a For Sale "One Humming Boat" and a phone number. Sorry about the last one I could not resist it !! Find a different slip! I have had a boat like that and it cured with just disconnected baby stay and radical mast bend but some are not that easy. Michael Pope

[zstine]

I have a 1975 Tartan 41 with the similar rig setup and have a similar issue. Try cranking on the babystay and backstay to put some bend in the mast. I have check stays, and for me, tightening those works best perhaps b/c the side load or that they are part way up the mast. Without check stays, try running the topping lift to the toe rail so it pulls on an angle and crank on that.


Sailing Diablo

[GordMay]

Greetings and belated welcome aboard the CF, Ozziediver.