Rebuilding the drum located the actual problem at the swivel on our 18. Our dealer (Jim Sohn) stated that over time, and without periodic lubrication, the swivel will develop "flat" spots. Lubrication got us by (needed replacement).

Berman describes marking the shrouds at three feet above the deck and stretching a tape measure straight across these points. I recall a six inch deflection, when pressing inward on one shroud, to be the heavy air setting. His book (the Hobie 18 Performance Manual) is filled with these type of measurements. A similar method is described for diamond tension by pressing inward to within one inch of mast and measuring up from their attachment points (12", 24" & 36") for varying conditions of "the three W's", wind, water and weight.