Thank you Arnaldo,
Your comments reflect your vast experance with physics, and sailmaking.
I still dont understand why you would disagree on the concept of a "best" all around design, for a given boat.
We have gone thru extensive on the water testing for various class boats. Much like what we would do during our windsurfing sailmaking days.
We would try differant luff curves, twists, draft positions, etc. Than we would switch boats, and sailors, to eliminate variables, and often arrive at a shape that would best perform over a range of conditions. Granted, as wind, and sea conditions change, the shape of the sails should change as well.
But, most of our customers here, don't want to hear that they should be buying not one new main, but two or three to be more competitive in all conditions.
If the sail is very flat, (like the Tornado main that you mentioned)there will be a lack of power, in the light air.
This will result in the boat not being to fly a hull as quick as the competition. This is a disadvantage, like a windsurfer not being able to get on a plane as quick as other competitors. As the wind builds, the mast will bend from the added mainsheet loads alone. This will further flatten the sail, by taking out luff curve. If the mast bends as much, or more than the luff curve in the sail, the sail will distort, the draft will move aft, and performance will suffer.
For these same reasons, a fairly full sail, with stable sail cloth, will automatically self flatten as the mast bends under increased mainsheet loads. The modern downhauls can further flatten the main as needed. In fact we have been suscessful using the downhaul to flatten, and add twist to mainsails in light air, extending their range even further. Jibs, are another story. The jib adjustments are very limited. But again, most racers that we deal with, want one best suted to the local conditions.
You asked, "why" to my statement, "In most cases,materials that have low stretch, light weight, and good durability are most perfered".
Multihull sailors in general, go thru extremes to reduce weight, especally aloft. A light sail, reduces weight, and makes the boat easier to right. Most of the advances in racing sailcloth has been aimed at reducing weight, and stretch. From windsurfers, to America's cup, to the Maxi catamarns, this applies.
My question is, "how"
How can a flexable sail be self flattening on a large multihull, with a non-flexable mast? My experance has showed me that big multihull sails just keep getting fuller, as the wind builds, especally if the material is not stable enough, or the mast doesn't bend.
These are my opinions, based on personal experance with small to maxi multihulls.
Cheers,
Dave