Viper 640 Class Association Forums

Viper 640 Public Forums => Sailing, Handling, Tips and Techniques => Topic started by: Doug Johnstone on August 16, 2014, 08:12:42 PM

Title: spreader sweep Carbon rigs
Post by: Doug Johnstone on August 16, 2014, 08:12:42 PM
The spreader sweep on my boat is the most aft setting.  There are two available hole settings on each side of the mast bracket to allow the spreaders to go forward in sweep angle.  Curious to hear what other Viperers (?) are setting the spreaders at and how are you measuring.  I.E. Distance between spreader tips (excluding shroud inserts) or some other method.

I am aware of the effects of pre-bend on main shape, and sweep on pre-bend.  Just trying to get some numbers. 

Cheers,

Doug.
Title: Re: spreader sweep Carbon rigs
Post by: John Leyland on August 17, 2014, 01:12:51 AM
Hi Doug,

It may depend on your sails.  We have North and use their tuning guide where it lays out how to measure.  See http://www.onedesign.com/Portals/106/docs/Tuning%20Guides/north-viper-tuningguide.pdf

This resulted in us using the forward holes and reducing sweep angle but had to drill them out a little to accommodate the standard bolts.

Cheers,
John
Title: Re: spreader sweep Carbon rigs
Post by: Jeff Jones on August 17, 2014, 01:07:46 PM
If you sail heavy, min sweep.  If you sail light, max sweep.

Title: Re: spreader sweep Carbon rigs
Post by: Doug Johnstone on August 17, 2014, 02:27:50 PM
Quote from: Jeff Jones on August 17, 2014, 01:07:46 PM
If you sail heavy, min sweep.  If you sail light, max sweep.

Interesting response that I didnt expect.  Why?

John L, thanks for the link.
Title: Re: spreader sweep Carbon rigs
Post by: Jonathan Nye on October 20, 2014, 10:23:25 AM
Long time no reply so for what it's worth...

With min sweep, as you apply shroud tension this pulls the spreader tips back (reducing shroud deflection). This in turn pull the mast at the spreader bracket back which straightens the mast and tightens the headstay keeping the sail plan from becoming overpowered.

Conversely, max sweep allows the middle of the mast be bend more easily so pre-bend is possible resulting in a softer headstay all things you want in lighter air. The way to accomplish this with min sweep is to go with less shroud tension.