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USNS Montford Point

Oct 24, 2013 02:08 PM

Tanker design repurposed as floating pier for Navy

Float-out from the graving dock in San Diego last November.

Courtesy General Dynamics Nassco

Float-out from the graving dock in San Diego last November.

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With USNS Montford Point, the first Mobile Landing Platform (MLP) for the U.S. Navy, General Dynamics Nassco has pulled off the remarkable feat of rethinking an existing commercial design and adapting it as a naval auxiliary that can be reconfigured for multiple missions — all for about $500 million per ship.

Montford Point is based on the 185,000-dwt Alaska-class tankers that Nassco delivered to BP between 2004 and 2006. If it looks a little different, that’s because it resembles a heavy-lift ship more than a tanker, with a low, semi-submersible cargo deck bookended by a high forecastle and a towering house.

“The midbody section is entirely new,” said Ian Busch, Nassco’s manager of initial design and naval architecture. “There’s a few things that are consistent; we maintained some planes of structure. … The rest is all new.”

Courtesy General Dynamics Nassco

A night shot taken slightly earlier.

Montford Point is designed to serve as a floating pier at sea, to save prepositioning ships having to go to a terminal onshore to offload materiel. Instead, the MLP will work with hovercraft and Joint High Speed Vessels to offload equipment for the Navy and Marines from large roll-on, roll-off auxiliaries and transfer it to smaller craft that will land it ashore.

It doesn’t really carry prepositioned cargo itself, although it can house three of the Textron-built hovercraft designated as LCACs, or Landing Craft Air Cushion. It will be based at the Navy’s staging post in the British Indian Ocean Territory of Diego Garcia.

The vessel’s crewmembers are civilians. Ocean Shipholdings, of Houston, won the initial operating contract with the Military Sealift Command. There are 34 MSC berths on the vessel.

Montford Point is 765 feet long, compared with 942 feet for the Alaska-class tankers, although the beam is the same, at 164 feet. The upper deck on both vessels is 91 feet above the vessel’s baseline, but the mission deck on the MLP is just 50 feet above the baseline — hence the dramatic profile. “At first glance Montford Point looks like there is something missing,” one Navy veteran blogged after seeing photos.

Courtesy U.S. Navy

Adm. Jonathan Greenert, chief of naval operations (third from right) tours the engine room in a section of the vessel where its origins as a tanker are apparent.

The vessel’s range is 9,500 nautical miles at a sustained speed of 15 knots. The diesel-electric propulsion comes from four Fairbanks Morse MAN 6L 48/60 6MW medium-speed diesels giving a total installed power of 24 MW and turning twin shafts. Nassco hired Converteam, now part of GE, as the power systems integrator.

Unlike the tankers, the vessel has a 2-MW azimuthing bow thruster to help it maintain position as a ro-ro ship steams up to join it. “Once the two ships are mated together, the MLP is the control ship for the pair of them and maintains not so much position as heading,” said Busch. “The intention is that the sea only comes from a certain angle so that the combination … leaves a smooth sea that the landing craft can approach in.” The ro-ro sits on the port side of the MLP, leaving the landing craft in the lee of both vessels.

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