Hi Malcolm, I have made several sets of sails and started from scratch on a new yacht and also converted a yacht to 2 masts.

I always used drawing and geometry. I used the fact that all triangles convert to 2 right angles. I have a method for calculating centre of effort as well, using a drawing, what do you do?

However I am impressed with the formula, a lot less than that would send me off to sleep quite easily.

regards Roy

The problem with doing the two right angle triangles was determining the right angle "side" length without drawing it out. The formula allowed playing with numbers until the right area was stumbled on. There was a lot of dust on top of that old "Mathematics for Telecommunications", but it had a worked example, which bypassed a lot of thinking.

Once I had a suitable set of numbers that gave the area wanted, it was drawing to scale and geometry. And, using a scale card cut out of the sail plan, finding the balance point. But it only needed doing once. The balance point of the sails was very near to the drawn center found using the school compass and halving angles, the average of the pair coincided with that for the whole plan. With more thinking, it might work with any number of sails. I did something similar with a cut out of the underwater profile to guess at the center of lateral resistance. I don't know if the idea was valid, but the yacht worked just fine.

There was that story of Edison getting prospective employees to figure the volume of a light bulb. Most used reams of paper doing calculations - the guy who got the job was the one who filled the bulb with water and measured that. Theory is fine, sometime you just need to look.