Thanks for that. Intresting site. My stiching is not of a quality that I would let anyone with a camera near. Luckily the glue/press/heat treatment* of the seams provides 90% of the stiffness/strength. Cross cutting also appears to make it easier for a numpty to get a sail that stays in 1 piece.
Saying that I have deliberately tried to reduce the material weight/quantity and patches in the new set so probably a good time to state publically that if they explode I will still be grinning, but may then revert to the conservative measured adopted for Born Slippy's current set which will result in overpatching.
R
*Heat treatment in this case means leaving the sail in the airing-cupboard over night then rolling over every seam before it cools down. Couldn't afford the "tool" that a pro would use.