A sailor who sparked a massive air and sea search off Sydney's northern beaches told authorities he swam to shore after falling off his yacht, and then caught a taxi home, oblivious to the massive operation that had been launched to find him.

Police on Tuesday are expected to interview the man, whose yacht was discovered floating about 18 kilometres out to sea off Barrenjoey Headland just after 4pm on Monday.

The Westpac Life Saver Rescue Helicopter crew took this photo of the abandoned yacht off the Sydney coast. Credit:Westpac Life Saver Rescue Helicopter

A passing vessel raised the alarm after discovering the seven-metre Etchells yacht, which appeared to have no one on board.

A NSW Police spokeswoman said a Marine Area Command vessel went out to the yacht, and confirmed no one was on board.