[quote=dmgbear55]I think ideally the daggerboards represent where the center of effort is applied at the water when going to weather. With a jib and main configuration the combined lifting effort of the two sails should work out to be at about the vertical center line of the daggerboards. If the center of effort is in front of the boards the boat will want to fall off the wind and when behind the boards the boat wants to round up. Adding 11 square feet of sail to the main changes this balancing act. In the case of my 5.2 neither the height of the mast or the clew position is changing, but there will be a little more sail working higher up, so the aspect ratio is only changing very slightly.
I asked Andrew at SLO this same question and here is his response:
There are a number of mitigating factors with the square top. As the breeze builds or in puffs, the top of the sail will twist off essentially depowering a little by reducing the effective sail area. This makes the sail appear closer to a pinhead with a similar center of effort. Additionally, the added area of the square top doesn't move the center of effort considerably (there is still plenty of area down low to keep the center from moving too much) though it will be a little further aft than the standard pinhead. In lighter air, you'll likely want to keep the mast a little further forward. We have many customers racing with these square tops and we haven't received any feedback regarding negative weather helm. I don't know if they have adjusted their rigs or if they are just using the sails with their stock setups. You should have enough adjustment with the rig to try the new sail with the stock tune and then adjust from there. I know this is not an exact answer but I hope it leads you in the right directions.
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So for now I will stay with the current lengths for the standing rigging. If I ever finish this project and go sailing I will report on how the helm works out. When I last sailed the boat several years ago I know I was happy with the balance of the helm when going to weather.
dg[/quote]
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