Vibration in Hunter Isomat mast

[Donald Farquharson]

I want to let my fellow Hunter 35.5 owners know that thanks to your advice I was able to stop the harmonic vibration in my mast and possibly save myself the cost of a new rig.
It turned out that by tightening all the standing rigging by 1/16 of an inch the vibration was stopped.
I had lost a boom some 12 years ago due to harmonic vibration and that was caused by the triangulation of the mast, boom and topping lift. After fitting a new boom I fixed that problem by fitting a rigid vang and eliminating the topping lift. No problems since.
Bottom line here is that Isomat rigs on a Hunter 35.5 are pronr to destructive harmonic vibration but they can be cured.

 

[walmsleyc]

I tune up my Legend 35 (the 35.5s were similar and had the same rig) using a loos tension gauge and generally follow the standard procedure for adjusting tensions.

Do you know how close or far you are/were to proper tension? I've never had any problems, but I also have the rig pretty tight.

Chris

 

[Alan]

The specs on my 35.5:"

Mast Rake, 17" (3%)
Cap Shrouds, 3000#
Intermediates, 1400#
Lowers, 3000#

I've won loads of silverware for years with her so I know these specs are ideal for best performance.

 

[walmsleyc]

I run at something like:

Rake ... note sure ... more than 1 foot and less than 2.
Cap(9/32) : 2400#
Intermediates(1/4):1100#
Lowers(5/16): 1500#

Running more that ~2500# on the caps is pushing beyond the 25% recommended upper limit. In order to keep maximum forestay tension, I just go for the 25% for the caps and then grink everything else to get the desired prebend.