Okay all you rig tune gurus, any suggestions?
in 8 knots of breeze we're seeing different sail shapes tack to tack: on port tack the the draft is more forward especially top 1/2 of the sail.
I did the "main-halyard-to-both-shrouds" test and the mast is decently centered. Lowers are set the same.
We're using doyles upwind but I don't think that should matter.
Maybe one spreader is slightly more aft that then other?
Thanks!
Doug Stumberger
Doug,
I'm assuming you're talking about mainsail shape and not jib, right? Also assuming that you've accounted for the effect that the GNAV is having on mainsail shape (i.e., the main will be flatter on the tack opposite the GNAV location -- i.e., if your GNAV is on the starboard side of the main, your main will be flatter on port tack as the GNAV presses against it, and fuller on starboard tack, just like a Sunfish main).
Beyond that, never hurts in general to measure everything as you're noting. Checking to see whether a spreader is pinned differently either in the bracket or in the spreader tips on one side vs. another. Shouldn't be an issue with sail manufacturer otherwise.
I still don't understand why we don't use some sort of gnav pocket on the Viper mainsail or the other boats that use gnavs. Wouldn't it make the shape smoother on the leeward side?
jason
I defer to the sailmakers, but I'm guessing it would make the sail construction more expensive at minimum, not sure what it would do to longevity depending on how the pocket attached around the mast, but I can't imagine it would help if it was some sort of zipper / buckle attachment like a 49er -- loads would be higher on a Viper main than a 49er. Not sure whether it would make the boat faster necessarily either.
In the meantime, Jason: when are you signing up for NAs and/or HPDO? Time to get back into Viper one-design mode -- if we all have the same setup, it doesn't matter much.
Peter, thanks for the comments. Sorry, yes, I am talking about the mainsail. Spoke with Brad today and he suggested lower tension may have been different due to different spreader length, socket location etc. which I'll look more closely at.
and you comments on gnav effect is helpful.
Quote from: Jason Hyerstay on July 12, 2012, 04:09:25 PM
I still don't understand why we don't use some sort of gnav pocket on the Viper mainsail or the other boats that use gnavs. Wouldn't it make the shape smoother on the leeward side?
jason
I'm not a sail maker but it seems to me putting a gnav pocket would just cause your Main to look and perform bad on both tacks rather than on just one tack. I'm sure if you asked they would build one for you and you could pay more for your sail with no perfermance enhancement.
Look at your lower shrouds on each tack. When we look up the mast side to side we take the GNAV off the mast so you see it the same.
I would base your rig.
First off, measure your mast-step to insure it is centered athwartships in the boat.
Then measure everything about the the rig, measure spreaders using a large square to assure your spreaders are symetrical. centered and have identical sweep and rake (height). Measure length to shroud along the spreader root, measure tball socket heights side to side to the bearing surface on both uppers and lower.
Measure your shrouds from pin end to bearing surface to ensure they are the same length. Measure the location of the headstay. Is it centered on the mast? Measure the main track, is it centered on the mast.
Once you have done this, you KNOW you're rig is square and you can then base your rig. Use a tape instead of the halyard for measure incolumn. It'll be much more accurate. If you remember your geometry, just a tiny bit of length at the bottom of the rig adds up to surprising much at the top.
I approach basing a rig using the sailmakers tuning guide. I haven't seen Brads but I'm sure it's very complete. Get your numbers on the beach, document them, layout on a computer, print and laminate them. Put them on the boat so the whole crew knows what's up. It'll help immeasurably.
Feel free to call if you have any questions Doug.
Quote from: Peter Beardsley on July 12, 2012, 04:31:17 PM
I defer to the sailmakers, but I'm guessing it would make the sail construction more expensive at minimum, not sure what it would do to longevity depending on how the pocket attached around the mast, but I can't imagine it would help if it was some sort of zipper / buckle attachment like a 49er -- loads would be higher on a Viper main than a 49er. Not sure whether it would make the boat faster necessarily either.
In the meantime, Jason: when are you signing up for NAs and/or HPDO? Time to get back into Viper one-design mode -- if we all have the same setup, it doesn't matter much.
Peter,
Tack loads on the 49 main are much higher than that of a viper. Skiffies regularly use upwards of 10:1 on the cunningham. I think the enclosed gnav would be faster but it would probably add a bit of cost to the sail.