Mast Pumping / Vibrating

[Ocean Girl]

Thanks guys,
This is some great info. I think the culprit is the cutter stay and possibly the backstay being too loose. I tuned it again, but since the wind is low I can't tell if it helped. Thanks again for the info.
Cheers,
Erika

[svHyLyte]

If the staysail stay is not backed up by runners, and it is very tight, vortex shedding in high winds can cause it to vibrate. With that, the connection at the mast will be excited and if the frequency of vibration of the stay is near the natural period of the mast, the mast will begin to “pump”. Think little pushes on the bum of a child sitting on a swing. If the little pushes are at the right frequency—i.e. match the rate of swing--in short order the child will be swinging merrily away. The trick is to change the frequency of the stay or mast—or use something elastic, like a spare line flipped over the near mid-point of the stay, or angled away from the mast—say under the spreaders and aft—as a damper to kill the vibration. Simply tightening the stays merely increases their natural period and may give rise to earlier vibration at lower wind speeds and may also increase the mast’s tendency to pump as Euler Buckling forces in the mast come into play with even minor displacements. Think damping.

[Sailmonkey]

I just eased up on my rig this weekend, The racer in me was tuning for windward performance......but the boat just doesn't work that way. It was way too light to see if I made much of a difference, but by banging the mast around it is less prone to keep oscillating after I stop beating it.

[Mango Bob]

I’m curious to conduct an experiment:

My thought is to rig a wind disruptor akin to the mainsails leading edge and hoist it up the main track while in port. If this disrupts the wind oscillations around the mast then the Carman Factor is proven true. A possible wind disruptor may be as simple as the mast steps that are hoisted up the main track by the main halyard. Hummm……