I doubt they went for a fun swim the evidence points to a man overboard. Both the main and jib were up but not set and I don’t know anybody who would swim away from there boat with the sails up unless someone was still on board. If were me I would swim off the back if got to hot but would hang onto a rope or ladder and tow slowly behind the boat but never without someone controlling the boat..Perhaps it was man overboard and the other 2 went to assist.

They turn the boat back release the sheets and remove heavy clothing before jumping in and possibly they are holding onto a rope but the current and wind drag them along and tires them out causing them to separate them from the boat. However it does seem strange as there is no safety or floatation gear missing or is there? Can the previous owner recount the exact number of life jackets?...Maybe the investigation will uncover more.. Just as a matter of interest there was another strange incident in Queensland when a few months back a catamaran of similar size washed ashore upturned and battered. It was reported missing in ((2005)) there was no info on its disappearance. Maybe it was stolen but it probably broke its mooring. It was reported to have very rusty engines suggesting it may have been adrift for 2 years..