Construction Details Spars Old windsurfer masts make great yards and booms for sails up to about 250 sq. They are lighter and stiffer than other options, and it really helps make the rig easier to manage. Bamboo poles also make great spars. Use them if they are available in your area. Cheap Pages for lots more bamboo info.
Curved spars are optimum aerodynamically.
You can cut the sail with a curve on the sides that attach to the spars, and then use the sheet to pull the spars into a curve, if you sheet from approx. Another approach I would like to try is to use a strut between the yard and boom, to stretch the sail tight and to bend a big curve into the spars. Theoretically, the tightly stretched sail will create stronger vortexes than one allowed to curve from sail pressure. The mast foot can be made adjustable fore and aft. Moving the foot has the effect of pivoting the yard up or down, and moving the CE forward or aft.