Adjust this!
If you think about it, when you add backstay tension, the front of the mast goes forward, which will definitely loosen the forward lowers and tighten the aft lowers-so what you are seeing is absolutely correct. The relative tension you have is generaly right in that it is better to have the forward lowers slightly tighter than the aft lowers to avoid the possibility of inverting the mast (forward bend). It also will serve to flatten the mainsail somewhat. If, however, you feel the main is already too flat, you can fix this easily by slightly adding more aft lower tension and less fwd lower tension-just make sure the fwds remain just barely tighter than the afts.
As for proper use of the backstay with respect to upwind performance, be careful-pointing in light air is maximized with LOTS of sag-or at least as much as you can get when you ease the backstay(but not so loose the HS is flopping around as you go through the waves)-this is because you are not at or near full speed, and you want the fullest possible genoa, and sag makes it fuller. You will be faster and higher in light air with a loose(ish) backstay. In light air, you will net the best pointing by getting the best forward speed, and then the keel will begin to help you point. If you just sail high and slow, there is not enough flow around the keel for it to develop enough lift, so you will be slow and end up not pointing well (in net terms).
BUT..when the breeze is up and you are approaching hull speed (although I hate that term), and you have a bit of heel, then the full genoa will have too much drag to be close-winded or fast. This is when you add BS adjuster to flatten the genoa, and thus reduce heel and leeway, which yields better pointing and speed.
Question: what do you mean by 10% and 15%? Of what?
Cheers,
seth
