Thanks Dave, I had always assumed that the percentages were area relative to the area of the fore-triangle. Boy was I wrong! I'm surprised the percentages make no account for luff length, since high wind headsails often have a shorter luff than the headstay, and some light air downwind sails have a longer one. My drifter was cut too tall and I had to get the luff cut down, but apparently that didn't reduce it's measured size as a percentage. Whatever sailplan Eliot-Pattison is using for the M15 is way off from what my boat is, I had to cut about 3" off both the main and headsails to make them fit. Surprisingly that doesn't seem to be hurting me any in the races against the newer M15s, but I suspect my boat is also a bit lighter because it has the absolute minimum on all options/features. Tyler '81 M15 #157 Davis, CA ----- Original Message ----- From: "Dave Scobie" <scoobscobie@gmail.com> To: "For and about Montgomery Sailboats" <montgomery_boats@mailman.xmission.com> Sent: Tuesday, August 4, 2015 8:32:25 AM Subject: Re: M_Boats: Drifter Sail Henry: details on the size of a headsail - http://www.jasperandbailey.com/tech/headsails.html