Australian coastguards say they are puzzled by the discovery off the Queensland coast of a yacht with its engine running, food laid out on the table, but no crew.
A laptop was also switched on and the global positioning satellite system was working.
Survival equipment, including an emergency beacon, and three life jackets were also found on board, but no life rafts.
The 12-metre catamaran was found 128km off Townsville on the northeast coast, but there was no sign of the three crewmen who had set sail from Queensland for Australia's west coast on Sunday.
The yacht's sails were up but one was badly shredded.
The KAZ II was spotted adrift on the outer Great Barrier Reef on Wednesday.
Rescue crews boarded the vessel today but there was no sign of the three crew men, aged 56, 63 and 69.
Rescuers have retrieved the boat's GPS system to analyse data to help them track the yacht's progress.
