Might be noted on the sail
Used to have a C27 with North Sails - the 170% (or maybe a 163% ??) had a notation marked on the head of the sail "18Knts Apparent MAX".Might be a good starting point. I bet you think about adjusting down from the No.1 a little before 18Knts though.Good Luck!Tim BroganApril IV C350 #68 (Used to be Inamorata C27 # 6111)seattle