Originally Posted by PG
I believe in the theory about diminishing returns, and a 10 m2 sail on a slalom board with a 70 kg rider starts to get there.
But it may also be that the 8.3 is a slalom sail, while the 10 m2 is a highwind formula sail that was never designed for any early planing!
I agree, a big slalom sail will have more power than a small formula sail.
At 70 kgs a 8.5 will get you going in very light winds with a 133 Isonic. The wider the board, generally the bigger the sail you need get it unstuck from the water and planing (diminishin returns...). Bigger sails also will push the nose down making it harder to get going. Hence formula gear goes with 1m wide boards. The entry to a formula sail is narrower, the sail flatter, all designed to upwind, and offcourse dead downwind. So at 70kg, its not your technique, its the sail.
Being 70kgs you may also find a 7.8 plus I107 will get you going pretty damm early also, but with a much better top end an ride.
I'm 95kg and I107 is my biggest board.