World's largest superyacht is now also the fastest

Klaus Jordan | Azzam

Building the largest superyacht in the world apparently wasn't enough for the owner of Azzam. They also wanted the fastest.

Yachting executives say that Azzam, the largest yacht in the world at 590 feet, recently went through its first set of sea trials in the North Sea. The boat hit a staggering 31.5 knots, or about 37 miles per hour. At that speed it's believed to be the fastest yacht longer than 300 feet.

And that's not even top speed. Engineers say Azzam—with 94,000 horsepower driving giant water jets instead of propellers—can go even faster in deeper water. The 31.5 knot speed was recorded in water only about 60 feet deep.

"It can easily do more than 32 knots in deeper water," said one executive close to the project.

Azzam was officially launched in April but won't be delivered to its owner until sometime this fall since it still needs to undergo further tests and finish work. The yacht, which cost more than $600 million to build, is believed to be owned by the royal family of the United Arab Emirates.

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Representatives for Lurssen, the company that built Azzam, declined any comment about the boat.

Azzam is nearly 30 percent faster than similarly sized yachts. Eclipse, the second-largest yacht at 536 feet, hits a top speed of about 22 knots. Rising Sun, the 453 foot megayacht built for Larry Ellison and now owned by David Geffen, hits top speeds of about 28 knots.

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There are smaller yachts that are faster, of course. A yacht called The World is Not Enough, a 140-footer built by the serial yacht builder John Staluppi, hit a top speed of 70 knots. But it's one-fourth the size of Azzam.

Fortuna, the yacht built for King Juan Carlos of Spain, hit 68 knots.

No descriptions or images of Azzam's interior are available, though we know it's in the hands of French interior designer Christophe Leoni, who's using a "turn-of-the-century Empire style."

—By CNBC's Robert Frank. Follow him on Twitter @robtfrank.