Sqare Top Main?

Have my original main on my H18, hull number 4549, and am looking for a new main. Was thinking about a square top but what penalty rating will I incur for a race like the Mug Race? Is the performance worth it?

Assuming it is not one design racing your penalty for square top is .995 as long as your sail area does not exceed 5% of original. If it does the penalty is .98 I believe. Check out www.ussailing.org and go to the portsmouth yardstick for ratings and adjustments. If you have a large one design class, stick to stock, if you are one of the only 18's go for it, it is a real nice mod especially for light air.