On Wednesday, a private yacht sailed slowly and quietly up the Hudson River and docked near midtown Manhattan.

This wasn't just any yacht, however. It was Eclipse -- the largest private yacht in the world. And its presence is sure to touch off a frenzy of speculation about its owners and future.

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Seeing Eclipse docked off the midtown piers is the boating world equivalent of seeing a blue whale swim up the Hudson in the dead of winter. It just doesn't happen -- or hasn't happened. Eclipse's owner, the Russian billionaire Roman Abramovich, is famously private and averse to publicity. Eclipse is almost always kept in the rarified preserves of Monaco, Cannes, Portfino or St. Bart's, visible to other billionaires but rarely the hoi polloi.

By docking the boat in Manhattan, under the gaze of millions and a horde of media companies, Abramovich is, to say the least, inviting attention.

A spokesman for Mr. Abramovich declined to comment on the boat or its owner's reasons for being in Manhattan. But several dock workers and officials who have been briefed on the boat say it is scheduled to be in town until mid-April.

Some speculate that Abramovich may be using the boat as a temporary residence, since it is more secure and can better accommodate his large security force than a New York coop or hotel. Abramovich's partner, Dasha Zhukova, has announced that she is pregnant, and due in the Spring.

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Eclipse has a crew of more than 60 people and a battalion of security cameras and sensors. It has two helicopter pads, two pools and a submarine.

At 533-feet, it remains the largest yacht in the world. But it may hold the title only for a few more months. A new yacht, called Azzam, is being built for a MIddle East billionaire that could be 590 feet.