sail making

[longtailboats]

Sail making question
Hello,
My first question and I do know I should make it simple and easy to answer. I am an experienced amateur boat builder who has built his first sailboat. This question is about sail making, something I have never done, the mast and boom are nearly finished. I’ve about figured out how to do it thanks to this great video at ehow http://www.ehow.com/videos-on_1864_sailmaking.html . My boat is a catamaran anyone can see at my site http://longtailboats.webs.com/ . I have only one question that has been nagging me concerning mainsail leech, luft and foot round. I have built the mast and boom modeled somewhat after the Hobie cat, where the lines run inside the sail luft, leech and foot. He is making a jib and that is different than the mainsail that I am making. In the video the leech, luft and foot are curved. I don’t see how that would work for a mainsail styled after the Hobie because the foot is captive in the boom so how is a curve even possible? As far as the leech and luft is concerned the lines would straighten the curve and bunch up the sail when tightened or will it bunch up? so the question finally is should I have any round, in the leech luft or foot of my mainsail and can anyone offer any advice and websites to go to for more sail making instructions?
Thanks from Thailand,
Thai Sean

[gonzo]

The curve, when it is forced into a straight track, is what gives the sail its shape. A flat sail will only work downwind.

[longtailboats]

Originally Posted by gonzo

The curve, when it is forced into a straight track, is what gives the sail its shape. A flat sail will only work downwind.

I stlll domt understand. I built a model sail and the way I cut the panels gave it camber. I dont see how ciuving the luft leech or foot does this or why. I need to know why.

Thanks
Thai Sean

[Doug Lord]

I'm not a sailmaker but have had many sails made to my planform design.
The planform, whether rectangular or triangular, will affect the sails' performance and is mostly a function of the designers preferences regarding how the sail will work with his/her design. The designer of the boat will also specify the degree to which the mast bends and the sailmaker has to include an allowance for that bend in the luff curve.
The section shape/camber is 100% controlled by the sailmaker and is based on his/her understanding of the intended uses of the boat as gleaned from the designer.
My personal preference is for a loose footed main as it seems to extend the correct camber as low as possible. But there are plenty of practical reasons for attaching the foot to a boom and in doing so the idea would be to keep the desired camber as close as possible to the boom before the material has to be fitted to the boom.
Hope this helps....

[Typhoon]

The only curves on the luff and foot of a mainsail should match the curves of the spars when they are set up under load. It's a really bad way to "shape" a sail. Same thing goes for the luff of a headsail.
Yes, you can alter these curves on an older sail to get more life out of them, but it's a short term fix.
Most performance mainsails have a shelf foot and that's not really the edge of the load bearing part of the sail. Loose footed mains have lots of advantages on smaller size boats, but there comes a time where a main is much easier to handle if it's attached to the boom.
The easiest, most accurate way to put shape into a sail, that will stay exactly where you want it, is to shape the panels.
The leech of a sail is curved into a hollow to help provide some edge tension that will keep any distortion under control on this heavily loaded part of the sail.

Regards, Andrew.

[messabout]

The best way to build your own sail is...don't. You have experience building boats, right? You know that there was a learning curve and you probably made a few mistakes with your first build. So be it with sails. It is not a terribly complicated process but the learning curve is likely to result in sails that will not do justice to your boat.

There are scads of used profesionally made sails that can be bought for the same or less than the cost of materials that you will need for home built sails.