take a look at this thread on the F16 forum: http://www.catsailor.com/forums/ubbthreads.php?ubb=showflat&Number=146087

Starting here: http://www.catsailor.com/forums/ubbthreads.php?ubb=showflat&Number=146080#Post146080

What you cannot see is that the blue D12 has a bobble on the bit that come up from the base of the mast and the D12 that goes around the block on the sail has a loop in it (to go over the bobble). Works like a dream; releases well.