It's 92 metres long and six storeys high - and is the largest private super yacht ever to visit Sydney.
The Mayan Queen IV, with its white exterior gleaming under the spring sunshine, docked at White Bay in Balmain over the weekend and is expected to leave tomorrow.
The yacht's visit is shrouded in secrecy, with its Sydney agent, Major Yacht Services, allowed only to reveal the craft is in town for a refuelling stop.
The yacht, built in 2008 in Hamburg, Germany, is owned by Mexican billionaire Alberto Bailleres, 78, who made his fortune in mining and logging.
Mr Bailleres is ranked at No.66 on Forbes magazine's March 2011 list of the world's top billionaires - with a net worth of $US11.9 billion ($11.6 billion).
The Mayan Queen IV is even more impressive when ranked against its peers, listed as the 37th biggest yacht in the world according to website superyachts.com.
The super yacht is so large it is almost one-quarter the length of the world's biggest cruise liner, Royal Caribbean International's 360-metre-long Allure of the Seas.
It has a cruising speed of 20 knots and a top speed of 22 knots, room for up to 16 guests and 24 crew and has a steel hull and aluminium superstructure, the site added.
The interior was designed by Terence Disdale and the exterior by Tim Heywood Design, both based in Britain.
As it's longer than 80 metres, the Mayan Queen IV falls outside the NSW Maritime regulations for ordinary super yachts, and it is categorised as a commercial ship instead.
This means it needs a pilot - a maritime term for an expert with local knowledge - who joins the boat when it is out at sea (in Sydney's case, at The Heads) and stands besides the skipper to help him or her guide the craft into the harbour, Neil Patchett of NSW Maritime said.
"There's been a large increase of super yachts visiting Sydney in the past 10 years," said James Thompson of Sydney Superyachts Marina in Rozelle Bay, where most large private vessels usually dock.
"The Sydney Olympic Games was the main thing that put Sydney on the map as a super-yacht-visiting destination. Since the Games we've seen many new vessels visiting Sydney, to the stage where we have now 50 plus visiting NSW waters each year, which is very exciting."
Mr Thompson said most of these vessels were based in the Caribbean or Mediterranean, but were now coming to new cruising spots - such as around Australia - in search of new playgrounds.
It is not known who sailed with the Mayan Queen IV, but Mr Thompson said super yacht owners did not usually travel with their vessels, but would fly in by plane to meet them in the city where they were berthed.
The world's largest super yacht, the Eclipse, is 164 metres long and owned by Russian business tycoon and Chelsea Football Club owner Roman Abramovich.
Just two metres shorter is the Dubai, owned by the ruler of Dubai, Mohammed bin Rashid Al Maktoum.
Al Said, ranked at No.3, is 155 metres long and owned by the Sultan of Oman, Qaboos bin Said.
These boats are so large some commentators have taken to calling them "giga yachts" instead of super yachts.
"There's definitely a 'mine is bigger than yours' syndrome in this industry and there is a desire to have the best," Jonathan Beckett, the chief executive of Burgess Yachts, one of the world's leading yacht brokers, told CNN last week.
"When you get up to 'giga-yacht' status, it is all about the best and these people are used to having exceptional possessions around them all the time."
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