question re-sail trim

Well said

 

Well said

 

Well,
I'd assume it's related to wind/air vortex shedding on mast & wires & associated occillations & harmonics... given that's a complex field & way way beyond my understanding.... I just accept that it happens, my "assumption" is that the pre-bend is offering the mast into a sprung state that reduces or delays the tendency of the mast/rig to go into some harmonic response.
I suppose the pre-bend takes the mast/pole out of column to a degree which might be a slight downside.
The three stay rigs with diamonds seem to be just a scaled up version of a beach cat rig, there may be some shortcomings in that simplicity maybe especially with the "soft" platform that beam cats sometimes have with hull bend/twist. The option of a forward strut that boxes(? unsure of term) in the action of aft raked side diamonds seems to offer better control. I had a rig to a 33' Beach marine cat that just had the side diamonds & it would occilate some but not too bad, most extreme once in just over 70knts but that was extreme conditions with the mast at the spreaders vibrating within about about 50-60mm/2" extra radius particularily in gusts from astern(bare poles doing 7-10).
Every sailboat I've been on seems to develop some kind of rig harmonic at times.... usually in bed at night with the wind howling... so you can stay awake thinking of metal fatigue or fall asleep and dream of it. The fact that rigs don't fall down too often & usually from some obvious and predictable failing of corrosion or fatigue that has gone uninspected for too long.... means that the pro riggers seem to get it right...
Would be great for some rigging pro or designer/engineer to comment.
Maybe at the mooring you can play the topping lift against the mainsheet to see if it calms down.

Jeff

 

That all makes sense. mainsheet tension doesn't seem to do much. I would like to hear from other cat owners just to see if they have the same phenomenon. It is not nearly as bad since I tightened down the shrouds, but it is still there. I plan to experiment with some bungees, and a little more bend in the mast via the diamond tension.