: snip

: I question your desire to use a tall sail. You went thru' a lot of effort to
: keep your boat from heeling and now you want to mount a very tall sail
: which can apply a lot of heeling moment to your hull. Since what you are
: doing is all rather experimental you could derive a lot of security and
: survive a lot of mistakes if you keep your sail's CE low and not too large
: in square feet. Because your boat is rather short it is not going to go
: fast. Once you get it near hull speed it is going to try to heel unless
: you dump air and slow down. Most of the kayaks that are adapted for sail
: have longish waterlines so they can use the high aspect sail effectively.
: Maybe "stretch" is the wrong word. Sail fabrics are mostly woven so
: they have "give" in one axis or another. Sailmakers use this
: give to get the shapes they want. Of course, once the sail is filled with
: wind they don't want the shape to change. There is no give in blue tarp
: material. I wonder if you can even get some sort of foil without having
: the material develop a wrinkle somewhere.

Hi Charlie,
A tall narrow sail on shorter hulls is sometimes necessary, for example, tall-banked rivers where a low, broad sail will be wind-shadowed. Chinese river junks used this aspect rig.

Most sails now have the panels cut by CNC, and the shape of the sail worked out on computer using NACA profiles to get the optimum shape of the complete sail.

Racing sails have almost no stretch in any direction, their shape is as fixed as possible. Mylar reinforced sails have no stretch, when they reach their limit, they tear. Rather catastrophically, which is why their usable lifespan is kept to a few races at most.
Cruising sails are primarily of Dacron for its low stretch, but it does stretch and lose its shape over time and use.

Using a non-stretch material for a sail just means you have to develop the shape through curved cuts and joins. Using wooden NACA templates makes sense for a prototype to find the best ways to cut for shape.
Wrinkles wouldn't be a disaster either, unless they were big enough to make enough slack to flap when sailing. The material would eventually give way at that point.

Hope this helps,
Mike Savage
South West Cork