Tuning the Carbon Mast

Started by Justin Scott, May 13, 2008, 09:28:47 AM

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Duncan Adams

Hi all,
I'm after some advice, we've jut put the new carbon rig in our Viper, but we're struggling to get it set up.
I've read on this forum and looked at the tuning guide but when we set it up with the 52.5" forestay we were dog slow and had massive weather helm? Our boat has a GBR sail number but I'm told it's the aquivant to #60. We have done all the other mods ( keel, chain plates) we haven't put the new rudder post on so I don't know if that's th difference?
When we had the Ali rig in our forestay was around 49.5" and as long as the mast was reasonably straight we can point pretty good and had good speed against the boats around us.
Any advice would be welcome.
Cheers

Garrett Johns

#16
Duncan, I am far from an expert on this but, I am guessing the first question the "expert" guys will want to know is
1. What sails (FYI, the carbon rig uses totally different sail cut)
2. Mast butt position
3. You upper and lower shroud tension
USA 129
Anacortes WA

Duncan Adams

Thanks Garrett, the mast is as far back in the fitting as possible, shroud tension was a little low probably about 24 on a Loos gauge. The sails are a uk loft, they are quite flat so that prob didn't help but we did have the mast quite straight (1.5" pre bend) to help. I took one of the toggles on the forestay out downwind and it did get a little better?

Drew Harper

Duncan,

Try two holes showing on the mast butt and 52" of headstay. That will ease up the weather helm. 1.5" of bend is risky if the breeze builds.

Where are your spreader tips located?

BEST thing to do is set the rig with 26 on the loos sail it and shoot some shots from mid-boom pointing to masthead. It'll be much easier to evaluate the rig  then.

With a super flat main, you will want some mid-mast sag to power it up a bit and want to block the mast partner a bit to keep the headstay from slacking. It's all a series of compromises.

What breeze are you sailing in? Are there any other Vipers around you to tune against.

Here's a couple of shots of our North main/jib and desired shape for the conditions. We were sailing in 6-10 knots TWS, flat water with 560lbs of crew weight. The rig was tuned North Base. 26 on uppers, 2 3/4 of blocking and slack lowers, Spreader tips all the way in, stock sweep, two holes showing on the butt.  
#189 UK Built Mark IV Viper "DILLIGAF"