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Old 05-08-2013
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Why round sail edges if there going to be tied to the mast and boom

I just dont get it, Why should I round the edges of my sail if once there tied to my mast and boom are just going to be flat. Am I missing something here? Its fustrating. Or are you supposed to keep the sail a couple inches off the mast and boom by attaching them looser. I understand rounding/ hollowing the leach but why the the foot and luff.

I read this somewhere else it makes no sense to me

"By rounding the edges of your sail, you will provide some curvature to the sail when the rounded edge is straightened against a mast or boom."

Last edited by MattMcc804; 05-08-2013 at 01:10 AM.
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Old 05-08-2013
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Re: Why round sail edges if there going to be tied to the mast and boom

If you are referring to luff curve, it along with broad seaming is how you get depth into the sail. When the mast is straight, the sail shape will be fuller. As you bend the mast it stretches that material between the luff and the leech and makes the sail flatter. Remember that most masts are not straight, they have a certain amount of pre-bend when sitting at the dock, and will bend even more when the backstay and sheet are on hard. The sail must be cut to match that pre-bend.
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Last edited by SchockT; 05-08-2013 at 02:45 AM.
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Old 05-08-2013
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Re: Why round sail edges if there going to be tied to the mast and boom

Luff and foot rounds were how draft was introduced to bolt-roped sails, especially in the absence of broadseaming, especially in small low cost boats. If you attach a convexly curved sail to a straight spar, a baggy pocket is generated near the mast and boom. Fill it with wind, that excess cloth becomes your airfoil shape. Not an especially great airfoil shape, but it was a cheap and quick way to accomplish that end. The preferred way to induce draft, especially with modern, low-stretch synthetics, is to build in draft by curving the seams between panels (broadseaming). This allows you to control the draft location and depth much better. But it is more labor-intensive than just cutting a luff curve. For the ultimate in airfoil shaping, sailmakers have begun molding the panels over three dimensional dies to get curvature just right. That's really expensive.

The other reason to build a positive curve into your mainsail luff and foot is, as ShockT notes, because most masts and many booms (esp. with mid-boom sheeting or vangs) exhibit a certain degree of bend. If your sail's luff and foot were straight, any flex in the spars would pull all the draft out of the sail and cause embarrassing creases. This Wayfarer mast pre-bend is a bit exaggerated, but you get the idea:



On some boats, pre-bend is critical for driving upwind, esp. in chop. It can also help the mast resist bowing forward downwind, which can be bad. Depends on the boat, tho. BTW, most headsails have a negative (concave) luff curve, to accommodate headstay sag.
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Re: Why round sail edges if there going to be tied to the mast and boom

Bobmcgov,

your post implies that luff curve is something that was done in the past. It should be noted that cutting curve into the luff and leech remains an important part of modern sailmaking, even on the most advanced sail designs. It is not just the domain of "cheaper" sails.
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Re: Why round sail edges if there going to be tied to the mast and boom

Wow this sail making stuff is quite confusing isnt it, no wonder they cost so much money.
I dont mind putting hours and hours into a sail I enjoy that stuff but it seems like ill be spending way more time trying to figure it out. Ill get a book
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Old 05-08-2013
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Re: Why round sail edges if there going to be tied to the mast and boom

Quote:
Ill get a book
I think someone mentioned in another thread that Emiliano Marino's Sailmaker's Apprentice, is a good resource. I agree. Or, if you don't want to figure our how, and just wnat to do, then you could also just order a kit from Sailrite.
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Re: Why round sail edges if there going to be tied to the mast and boom

Latteen sails should be cut flat. Polytarp Sails is simply mistaken about this. The shape is introduced by allowing the boom to rise at the end.
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Re: Why round sail edges if there going to be tied to the mast and boom

I think you're overanalysing all this.. as an auxilliary kayak sail it can be pretty simple. You're not trying to with the America's teacup, and it's never likely to go as well to weather as you paddling...
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Re: Why round sail edges if there going to be tied to the mast and boom

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Originally Posted by Barquito View Post
I think someone mentioned in another thread that Emiliano Marino's Sailmaker's Apprentice, is a good resource. I agree. Or, if you don't want to figure our how, and just wnat to do, then you could also just order a kit from Sailrite.
Ordered it a few hours ago, Ill have it in 2 days

Last edited by MattMcc804; 05-08-2013 at 03:56 PM.
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Re: Why round sail edges if there going to be tied to the mast and boom

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Originally Posted by Faster View Post
I think you're overanalysing all this.. as an auxilliary kayak sail it can be pretty simple. You're not trying to with the America's teacup, and it's never likely to go as well to weather as you paddling...
I dont paddle anymore and can maintain 4 knots in 10 mph winds. And thats with a rugged plywood leeboard and it has to create lots of drag. And thats with a 20sq ft poly tarp sail crudely made, I dont know if it can tack well yet but ive been able to sail away and sail home. Once I get my book Im going to sew something nice from 4oz dacron, A bermuda if I can figure it out. Oneday I would like to use this sailing triak in the everglades challenge a 300 mile race/expedition to the everglades. Of course, I have a long way untill then. One benift is I live on the water and sail, and learn everyday
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