The "Hula" Mast...

[PaulR]

History: we had to recently drop the mast on our San Juan 28 to haul her via road from her old home to the new. Mast restepped and tightened the best of my knowledge.

OK, we are undergoing one of our usual fall wind storms for Alaska, and I went down to the harbor to see how things are holding up. Seems our mast is shaking badly where the lower strouds attach to the mast. Shakes to whole boat and is really worrying us with what stress it is putting on the mast. Almost like the mast is doing a hula dance. Winds are coming off the stern at 20 gusting 30 mph.

I have followed every recommendation folks have had and have everything tightened accordingly:

Forstay is 7/32 and is set around 960 lbs.
Lowers are 1/4 and are set at 900 lbs.
Uppers are 7/32 and are at 840 lbs.

I have NOT done any adjustments to the rear stay (3/16) since the mast is raked back a little and we do not want it back further. To the feel it is right. But maybe it does need some tightening? Or is something too tight?

Under sail everything has been fine with the lee side a bit loose.

Any help would be great. I just hope we ride through today's storm OK!

Paul
Martha J
Homer, Alaska

[Brion Toss]

Hello,
I will guess that the prevailing wind blew from a different direction in your old marina. When you say that it was "off the stern" in this storm, do you mean dead astern? A broad reach? Nearly a reach? The kind of shaking you are describing is usually associated with vortices forming as the wind passes the mast, particularly side-on. When the formation and collapse of these vortices is harmonic with the mast's own moments, you get the shudders. Very hard on things in the long run.
Tuning will probably have a negligible effect on the problem, but do try hoisting a boat fender, with downhaul, on the main halyard. Take it up slowly, and the pumping will very likely stop when it reaches somewhere around mid-mast. Really. If this works, we can suggest other, less odd-looking procedures.
Fair leads,
Brion Toss