All the vessel's sails were up, although o­ne was badly torn The drifting yacht

One theory is that members of the three-man crew fell overboard in bad weather conditions, greatly diminishing the chances of finding them alive.

A search now has been scaled back to the north Queensland coast, in the hope that the crew made it to shore.

The Kaz II was found with its engine running and a table laid for dinner.

But there were no signs of any people.

Mysterious disappearance

The boat left Airlie Beach o­n Sunday bound for Townsville o­n the first leg of a voyage around northern Australia.

The 12m (40 foot) catamaran was spotted by a helicopter o­n Wednesday drifting off the Great Barrier Reef, but a rescue team o­nly reached the boat o­n Friday, and confirmed that there was no o­ne aboard.

"The engine was running, the computers were running, there was a laptop set up o­n the table which was running, the radio was working... and there was food and utensils set o­n the table ready to eat," said Jon Hall, a spokesman for Queensland's Emergency Management office.

"It was a bit strange," he added.

All the vessel's sails were up, although o­ne was badly shredded, and lifejackets were still o­n board.

Mr Hall said rescue workers had recovered the boat's Global Positioning System (GPS) device, which might give them more clues as to the crew's whereabouts.

"That will now enable us to track backwards where this yacht has actually been in the last few days, and we're hoping that can pinpoint the search area for the missing crew," he said.

Australian media reported the names of the sailors as skipper Derek Batten, 56, and brothers Peter and James Tunstead, ages 69 and 63.

The three are neighbours in Perth, Western Australia.

The Australian Maritime Safety Authority said the men were planning to sail around northern Australia to Western Australia.

The KAZ II is now back in port.