Centerboard optimization

[mustangermatt]

I am making a couple of changes in the centerboard area on my Coresound 17. First after an email conversation with Graham I have moved the trunk aft 3 1/2". I am using slightly different sails than the design (snipe cause they are cheap used and plentiful :-) which pushes the balance aft a little. We had originally discussed "a couple of inches" but when I rechecked my calculations I realized I had not taken into account the roach on these sails. Also the board foil changes below will move the center of lift on the board forward.

The second change will be the cross section of the centerboard. On the plans it is basically a flat board with nice fairing fore and aft. I researched board shape and came up with thethickness should be 8% - 12% of the chord length for a slow moving foil (most sail boats). This will provide more lift and a higher angle of attack before stall. So my board will be 1.4" thick, almost 1/2" thicker than the plan. I found a table of offsets for NACA foils that I am using to get the cross section. The board will be foam core glass with a Poplar stiffener (1.2" x 3.5") at the widest part of the foil to take the side force of the board against the trunk. The head of the board will be as drawn in the plan. I will also use the same NACA foil scaled down for the rudder and similar construction.

I figured it was ok to experiment with the rudder and board foils since they are easily replaced if I screw up. The one I worry about is the trunk placement since that is permanent, but I am pretty confident that I calculated it as close as can be on paper. :shock:

[mustangermatt]

Very good point. I was also thinking that if the balance is wrong I can change a lot by moving the pin. I also read about a guy who races IC's with his board raked forward, and wins consistently. You are right, nothing is permanent