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  #1  
Old 12-26-2016, 10:43 PM
tdem tdem is offline
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Recutting skiff sail

I sail a small one man trapeze skiff (Farr 3.7) and bought a second hand carbon rig for it to update it. I'm having trouble making the sail that came with it work, especially in light wind conditions.

The mast is a wing-ish shape, over rotating. Below the hounds is quite stiff fore/aft, while the top is more flexible. There are just the three stays, no spreaders (someone has cut them off in the past).

I've posted a couple of pictures, one with all the controls off, except the outhaul is quite tight. The other is with much more mainsheet and downhaul tension. Normally the vang would also bend the lower mast a bit more, and in 15+ knots it just about works. Below that wind strength I have trouble pointing.

Camber is about 13 or 14% at the lowest two battens. I have not found a way to get it less than this without pulling on a ridiculous amount of vang.

Would recutting the luff curve solve these issues? The sail is pretty worn in places so I'm wanting to do it myself to not waste money on something that doesn't have a ton of life left in it.

I was thinking of measuring the current camber at each of the battens, then calculating how much shorter the curve needs to be for a better shape. But I'm not sure what number to shoot for.

Any suggestions? Any way to mock this up without cutting into it? I have an old dacron sail which sets very similarly, so this could be experimented on first.
Attached Thumbnails
Recutting skiff sail-img_0599.jpg  Recutting skiff sail-img_0601.jpg  
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  #2  
Old 12-27-2016, 12:02 AM
gggGuest gggGuest is offline
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Are you sure what you feel is a ridiculous amount of vang really is? Some rigs do use big loads. And are you sure you are pulling on enough downhaul. That will tend to bend the mast and take out luff round, and some modern rigs need truly epic amounts hauled on. Looking at the photos more downhaul is my first thought.

This seems like a fairly conventional 3.7 rig at this distance and my very limited knowledge - AIUI no spreaders is quite usual now. Are you sure this is the right place to ask the questions? They do seem to be a bit idiosyncratic. Can't help thinking that fellow 3.7 sailors will be able to offer you much more informed opinions than anything you'll get here.
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  #3  
Old 12-27-2016, 02:12 AM
tdem tdem is offline
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The problem with vang is it pulls the roach over to windward, right when you actually want twist in light winds.

I've put some stiffer battens in the bottom pockets, which slightly helped.

I just rigged the sail on the boat and there is really no combination of settings that gives me a flat-ish sail with some twist like you'd want in light winds.

The 3.7's pretty much all have different rigs, although simpler rigs are more common (not over-rotating). I'll be looking and asking around for sure.
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  #4  
Old 12-27-2016, 05:54 AM
gggGuest gggGuest is offline
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Quote:
Originally Posted by tdem View Post
The problem with vang is it pulls the roach over to windward, right when you actually want twist in light winds.
Normally large amounts of downhaul will open the upper leech.

If its genuinely over rotating though then it marches to a very different drummer. The amount of rotation is a key setting. More rotation will tend to flatten the sail by taking out luff round as the mast bends sideways, but also make the leech stand up. My feeling is that you could try with a lot more rotation than is shown in those photos. I haven't played with an overrotating rig and a really modern style sail, I'm a bit out of date in that respect, but its such a rare combination you may have trouble finding folk with good experience. Strangely I never found info from multihull sailors to be that much help trying to set up an over rotating rig on a dinghy, their concerns seemed to be utterly different.

Frankly I've found over rotating dinghy rigs to be such complete sods to tune and so finicky to sail with that the odd burst of speed didn't seem to make up for the frustration. I'm sure there's potential there, but I haven't raised the enthusiasm to have a go with them on my last few boats.
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  #5  
Old 01-02-2017, 05:04 AM
JRD JRD is offline
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That sail looks like it was cut for a standard round mast. Once you have vang tension on a 3.7, the mast bend is fairly even (and well more than is evident from your photos). 50mm of extra bend below the hounds would suck a lot of camber out of that sail.
I would expect a sail cut for a wing mast like this to have a straighter luff curve than can be seen in your photos.

If you want the boat to sail fast and point well in racing I would get a sail maker to do your recut. I have had a 15 year old sail re-cut with great results.

There are people in the 3.7 class who will know the history of that boat and rig, so advice should be available without too much effort.

Here are a couple of links to videos about NS14 tuning as these use a similar wing mast and the relationship with the sail is similar to the one you have.

https://www.youtube.com/watch?v=_C_qqyqNt04
https://www.youtube.com/watch?v=5Q0ovCn1Yxs
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  #6  
Old 02-08-2017, 03:49 AM
tdem tdem is offline
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Just thought I'd give an update on what I ended up doing. I took the luff tape/bolt rope off up to the top batten and drew a new curve on the sail, based on measurements and putting the mast and luff curve into a CAD program. Then stuck the luff tape back on with duct tape, allowing me to test the shape without any cutting. Adjusted a few times until it was looking plausible and then cut the luff. Stuck the luff tape back on with double sided tape and got it sewn back together.

Just came 5th in the Nationals using the re-cut sail. The boat was going much better, especially in light winds. Very happy!
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Old 02-08-2017, 06:55 PM
CT249 CT249 is offline
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Well done. I've wondered about using duct tape for experiments myself. How tough was the double sided tape in reality ie on an old sail? I used to sail on a sailmaker's Mumm 36 and they used to test their own sails out when they were just taped together, but I wasn't sure whether that would only work with new sails and the right amount of skill.

What was it like using the duct tape? Obviously you could use a reasonable amount of static pressure but did you test it sailing at all?
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  #8  
Old 02-09-2017, 01:57 AM
tdem tdem is offline
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I used basically office supply double sided tape which is probably not as good as the "real stuff". It did not stick that well to the luff tape which was very heavy dacron, so not that smooth. It did however last a full night and being transported in the car after.

The duct tape was not the branded stuff, but stuck really well to the sail and came off without leaving any residue. Because of the full battens there is quite a bit of pressure on the luff at the point where you are feeding it into the sail track, while hoisting or lowering, and this is where it let go a couple of times. I didn't do any sailing but think it would have worked. It seems to creep though when left under stress, and lets go over time.

If you search around there's a bit of info on taping sails together, especially for polytarp sails.

From http://polysail.com/library.htm "Note: Rubber-backed carpet tape alone will normally last for a few uses without sewn reinforcement, but this adhesive eventually dries out and loosens from the slippery polytarp surface. Double-faced acrylic tapes tend to bond better with polytarp since the bond improves over time. If acrylic tapes loosen, they can usually be re-stuck.to the material. These more expensive tapes are used in our NO-SEW PolySail Kit.
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