Stavanger, Thursday
Barrel-cut versus Tyler-tucks
David,
I looked up the sketches about your tuck method and the Tom Thumb sail plan. The method no doubt is easy to understand involving no rocket science whatsoever. The knuckles you mention will be no problem, just as on Badger.
(..I too was concerned about sharp corners in the sail when making hinges in the battens for Malena, 20 years ago. No problems there either; the horizontal curves in the panels were nice and smooth...)
I also noticed on Badger’s sail (similar tuck method) in 2006 that the vertical curve from batten to batten was closer to trapese-shaped than "my" sails. In a way you get closer to the shelf foot method without all that extra brainwork, cutting and sewing. So this looks good and will probably sell better too.
So why don’t I jump over to the "Tyler-tucks" from my present "barrel-cut" method?
1) A bit from laziness of course – I am so familiar with my way of doing it now – and I don’t have to sell sails. But not only because of that:
2) The barrel cut method is still quicker to make for an amateur and without any folds getting in the way when assembling the batten panels with my household sewing machine (no walking foot). All you need extra is a nice long spline to produce those "barrel side" curves.
3) I find it hard to believe that the small wrinkles that one may get along the battens with the barrel cut method will slow the boat noticeably down. I notice that Johanna is the only boat in Stavanger which really has these wrinkles. This summer I’ll stretch the sail a bit more along the battens to get rid of them. Then I’ll check how much influence this has on the max camber.
4) At the max camber point a vertical curve through a barrel cut panel will be more rounded, not trapeze-like at all. This makes it easy to think that the camber varies a lot and that the sail therefore will be less efficient. However when moving towards the luff or leech, these vertical curves will get closer and closer to the trapeze shape. This I noticed as early as on my first test panel in 1993 (see NL30, p.22). My hunch is therefore that the wind will enter a sail at pretty constant angle of attack along the luff and also leave it that way. If my hunch holds water, then the shape of the barrel cut panel should be just as efficient as one made with tucks or with the shelf foot method.
Sooo, until someone with a similar boat as Johanna comes over and sail in rings around us with their clever sails; wings, split-rigs, shelf foot method or whatever, I'll stubbornly stick to what I have.
Arne
PS: These days I put another layer of 2-pot varnish on Broremann’s new mast every day. I ache to get a sail in Broremann soon...