Ta for info on sail sailor...mk 4 !!??..still seems to keep reasonble/good pace on the mark 6's ive been been against. Your bottom section (mast).. does it have any small prebend? this one does and i think it makes the sail too flat compared to sail area above window The strange settings of a lot of outhaul,no cunny , and small vang load ,,upwind in 8-10 knots and it flew and pointed,,lots of learning ahead...see ya