Big wind = easy to explain. You got to much power and you need to loose it in an efficient manner. Flat sails have a higher lift to drag ratio because by flattening your reduce drag more then you reduce lift. Both are reduced at the same time but drag is reduced alot more. So the boat feels LESS power-up but you get a better net drive and hence you go faster.


Very little wind = The sail is often to wide (cord) with respect to the energy enclosed in the movement of air particles; this means that the flow (particles) detaches from the mainsail before it (they) has reached the leech. This is when the sail is kept with a full draft, something many sailors believe they should have as to gain maximum drive. In effect the particles have insufficient momentum to follow a significant curve in the sail (draft) and they detach themselfs = stalling of the mainsail. This adds ALOT of drag. Now by reducing the draft sufficiently the particles will be able to follow the full curvature all the way to the leech without "stalling". The mainsail is now streaming again. This will again both reduce lift and drag but by reducing the drag ALOT more thus the net drive is increased and you'll go faster as a direct result.

The twist in the leech of the main in very light airs is because in these conditions the windspeed in the first 10 mtr of the ground will show a significant offsets in speeds. The resulting direction of the apparent wind flow at ground level can easily be 20 to 30 degrees more along the centreline then at the top of the mast. If you sail without any twist then either the top of your sail has stalled or the bottom of the sail has been completely weathervaned. Solution, sail with a significant amount of twist.


Typically sail with 200-300 mm twist along the leech on a F16 in nearly all conditions (Advice by Glenn Ashby with respect to modern LARGE squaretop sails). My experience is that you significantly want to increase that in the really light winds. Now the only way to get this twist profile and still have a flat mainsail (little draft) is to derotate your mast and really crank on the downhaul.

On the Blade/Stealth F16 you also want to lift your luff hull clear of the water by doing the wildthing. Taipans are more forgiving in the respect and it doesn't hurt then to much when part of the luff hull is still in contact. However, doing the wildthing on the Taipan really helps as well. Why, it reduces the total wetted surface area by something like 15 - 25 %; this can easily translate into 7% to 10 % more speed. And that is the difference between winning and finshing mid fleet in very light winds.

In light winds you have to keep moving all the time ! Getting up to speed is more difficult then maintaining speed.


One race last year. I was 200 mtr back of a pack of 4 I-20's and 5 F18's in such conditions. I did all the above and coached my boat gentle up to speed. I overtook all boats ahead of me except 1 F18 and I sailed through all the lee sides (wind shadows !) to reach the finish 50 to 150 mtr ahead. Best laugh I ever had; you should have seen their faces. They still claim I had my personal gust (for nearly 400 mtr and nearly 3 minutes while passing the others only 20 mtr downwind !)

I know it was the sail trim, because I knew exactly when I started to really move and what preceded it. I had cranked on alot of downhaul and this allowed me to slacken the mainsail to introduce alot more leech twist while maintaining a shallow draft.

Hope this helps

Wouter