right pepin i'd forgotten about the large overlapping gib
not sure if it's wise to put a square top on the older straight spreader masts, apparently difficult to depower in higher winds, i mean when was the last time you saw a square top on a hobie 16?
as it's generally a light air lake what about a furling code zero gennaker like the weta trimaran has
should be able use it up tacking upwind and gybing downwind
new weta video here
http://www.wetamarine.com/GALLERY.aspx not related to gennakers but a nice main only gybe at the end of the video