After the U.S.S. Cole was attacked in Yemen in October 2000, the Navy needed to get the damaged ship to Pascagoula, Mississippi for repairs and refit. But you can’t just tow a ship with a 40-foot hole in its side through the Indian and Atlantic Oceans and hope it stays afloat. So it hired Dockwise, a Dutch shipping outfit whose specialty is moving enormous pieces of cargo.

Dockwise sent the MV Blue Marlin, which sailed up to the Cole and used its huge ballast tanks to submerge itself. It slid underneath the destroyer before rising up and lifting the entire ship out of the water, and carried it just like any other cargo. The 505-foot Cole easily fit on the Blue Marlin’s 584' x 206' deck. It was successfully moved from Yemen to Mississippi and returned to Navy service within a few years.

Impressive at the Blue Marlin is, it pales in comparison to its younger, much larger brother, the Vanguard. Built in 2012, the world’s largest float-on/float-off ship doesn’t have a traditional stern or bow. All its buoyancy casings, which keep the ship from keeling over, including several that are movable to accommodate different loads, are mounted on the side of ship.

That way, the unobstructed 230-foot wide loading deck runs the length of the 900-foot ship. This allows Dockwise to move loads that may exceed even that impressive length by having enormous items like ships overhang its stern or bow. This thing could carry the Chrysler Building.

Formed by the 1993 merger of two shipping companies, Dockwise is the world’s largest operator of heavy-load “semi-submersible” vessels. It’s used extensively by the world’s navies as well as energy exploration companies looking to install and redeploy offshore drilling platforms for oil and gas development. Though some competitors operate semi-submersibles, Dockwise says its focus on this technology and its fleet of more than 20 ships make it unique in the shipping industry.

The Vanguard is semi-submersible thanks to enormous water tanks that slowly fill to submerge the the ship by more than 50 feet. It can then slide underneath ocean-going behemoths like offshore oil rigs, lift them up, and transport them across the ocean at speeds as high as 14 knots (16.1 mph) thanks to its 27 megawatt twin-screw propulsion system.

Upon arrival, the Dockwise ship submerges again and slides away. The company says the Vanguard’s ability to transport enormous rigs weighing as much as 110,000 metric tons fully assembled can save companies time and big bucks. Its next largest ship, the aforementioned Blue Marlin, can only lift structures up to 76,000 metric tons, and is limited by its more traditional ship design with both a bow and stern.

As an added bonus, the Vanguard can act as a drydock, lifting enormous structures for maintenance and overhaul at sea, rather than wasting time and money by hauling them back to land.

The Vanguard was even selected to remove the capsized Costa Concordia cruise ship from the coast of Italy, but it seems the deal fell through.

Source: www.wired.com

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