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Old 17-10-2009, 16:46   #16
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Originally Posted by matoi View Post
Sorry for a digresion from main topic, but could you please explain why is a non overlapping jib so important. I thought that non overlaping sails are much less effiecient. Thank you. Mato
It all depends on the design of the boat, rig and sailplan. You have sloops with a small main and a big genoa and you have sloops with a huge main with a big roach and a small jib. As boats become big, a big main is much easier to handle than a big (think 140%) genoa.

Most, but not all, cats have the big main. Most older mono's have the small main. Trying to change from one to the other is difficult because the mast and chainplates should be moved.

You are referring to the slot effect between jib and main. Yes, that is important for the "old design" sloops. The modern ones sail fast with main alone while the older type sails faster with genoa alone.

A high aspect cut also make a more efficient foil. A 95% jib can also be pulled further midships for higher pointing and this is more important when the beam becomes wider, like a cat.

cheers,
Nick.
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Old 17-10-2009, 16:48   #17
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Originally Posted by neelie View Post
Some questions :

1) How does one know what a "good" compromise size is for an asymmetric spinnaker?

2) How does one decide what a "good" shape is for general purpose cruising?

My confusion is because I have had competing sail makers suggest 1300 sq ft and 2000 sq ft respectively, both were given identical information, measurements and photos of the boat. I have been told both were "computer modeled".
Now I'm really discouraged and have given up the idea of getting one. With my luck I'll choose the wrong one.
It sounds like you need at least two more quotes. I think a mistake was made because that difference is too much.

cheers,
Nick.
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Old 17-10-2009, 20:59   #18
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neelie, i think you need a discussion with your prospective sailmakers. first, they should be able to tell you what design makes sense for "general purpose" cruising. second, you should explain how you sail your boat, what conditions you've seen, what sails you've used, and what you like/don't like about your experiences. your sailing style goes along way toward determining whether you want a conservative chute or an aggressive one. i would have guessed that a conservative chute would be just a fraction (1.2 to 1.6x) bigger than your mainsail (assuming you have a fractional rig). good sailing...
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Old 17-10-2009, 21:37   #19
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Quote:
Originally Posted by neelie View Post
Some questions :

My confusion is because I have had competing sail makers suggest 1300 sq ft and 2000 sq ft respectively, both were given identical information, measurements and photos of the boat. I have been told both were "computer modeled".
Now I'm really discouraged and have given up the idea of getting one. With my luck I'll choose the wrong one.
I don't know what is right for your boat, but as a data point we have a 2000 sq ft asymmetric on our Catana 48 and it works great. For us I'd imagine the 1300 would be frustratingly small in the light stuff.

As has already been suggested, have a discussion with your sailmaker. Don't just ask for a quote. They should be able to explain why they chose those sizes, not just that is what the computer spat out. I've personally had good experiences with Dave Calvert from Calvert Sails FL in getting good advice and nice sails for our catamaran, but I'm sure there many other good sailmakers out there who know catamarans.

Regards,
Mark.
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