At our YC we have two hoists .... the best would be to borrow/aquire/purchase a "loadcell" of a suitable range & accuracy (Mr SRM is quite correct in his analysis/comments) ...hang it on the hoist ... make up a bridle/harness ... and pick the boat up. (This is basically the set-up they had at the 2007 Hobie TheMightyHobie18/17/Youth/Womans North Americans in Geneva NY ... worked nice!!!)

Harry
H18Mag/P19MX