And should it be the same at the top as the bottom Mast pockets is what I'm talking about. When I knocked together the sail for 'Test Bed' I just took the max spec size from the Class 5 regs which I think was 140mm flat. I've just spotted an article explaining windsurf downhaul about the bottom of the sail being the 'engine' and the top the 'exhaust'. And that the bottom needs the battens close to the mast to get the correct shape but away from the mast at the top. Is this correct? Should I tighten the pocket to be close to the mast (not too tight to stop easy movement) then run the stitching straight along the pocket or should I follow the mast's taper Thoughts from the experts please, as currently the sail is like an on off switch, literally nothing happens till the wind picks up then it's off like a rocket