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

The Kaz II was found with its engine running, and a table laid for dinner, but there were no signs of any people.

An air and sea rescue operation has been launched to retrace the yacht's voyage, and pinpoint the search area.

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.

Rescue crews say they are puzzled by the mysterious disappearance.

"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.