there are various opinions about shaping battens.. some say yes, some say no.
phil berman in one of his books actually had measurements and percentages all layed out for each batten.
The basic rule i've worked with, (and i don't remember the exact measurement, but it can be found somewhere) is that you want your draft or pocket of the sail approx 1/3 of the way from the mast. IT MUST BE CONSISTANT ALL THE WAY UP THE SAIL! If it's too soft at the bottom and too stiff at the top, it is not fast. or vice versa. also, if the pocket is too deep or too shallow, it can reduce effective speed as well. There are people who understand the dynamics of areodynamic lift and can explain better for sure.
.. Some people measure the depth of the curve, some measure the pounds it takes to bend the batten. The hard part is making it consistant. Usually the top 4-5 battens need sanding, but be careful, you can't put back what you've taken off! Sand a little, measure/check, sand some more, measure check. A good way to check is to lay the boat on the side, sail up, battens tight, then look up the mast... Or, you start with standard battens, file a bit, go for a sail... repeat the process till you're happy(er). The main factor is to go slow, a little at a time, until you've got the shape you want.
Cork Guy wrote:
How about shaping or filing the battens for more sail shape in low wind
You only shape for one type of wind if that's all you sail. Shape for general speed then use your line adjustments for more control (downhaul, outhaul etc.)