New damage stability system from Japan

Conceptual drawing of righting moment recovery system Conceptual drawing of righting moment recovery system

Mitsubishi Heavy Industries (MHI) in Japan says it has developed a system to enhance the damage stability of ships, enabling reduction in capsizing risk, and has received the first order for the new system for a ro-ro cargo vessel.

The order comes from Nippon Shipping, a subsidiary of Nippon Express, which is building the 170m long ro-ro ship at MHI’s Shimonoseki Shipyard & Machinery Works with delivery slated for March 2013.

MHI developed the system in response to the strengthening of regulations on ship stability, based on revisions to the SOLAS Convention adopted by IMO in 1974. The newly patented system is targeted in particular at ro-ro ships, pure car and truck carriers (PCTCs) and ferries. With such ship types in mind, MHI developed the system with an emphasis on low cost.

If the ship’s hull is damaged at sea, the system transfers flooded seawater into void spaces in the ship’s bottom, thereby reducing capsizing risk through enhancement of righting momentum by quickly lowering the ship’s centre of gravity. It takes advantage of void spaces near the ship’s bottom by utilising spaces allocated to other functions: e.g. fin stabiliser rooms, duct keels and ballast water tanks. Holes and watertight covers are provided to feed the seawater into the void spaces, and pipes are in place to serve as air vents.

The system enables rapid water filling and lowering of the centre of gravity to cope with emergencies. The system is claimed to eliminate the need to divide the vehicle deck area into small compartments thereby avoiding sacrificing vehicle capacity while facilitating smoother vehicle manoeuvring within the ship.

The company sees its new righting moment recovery system as another promising technology that will sit alongside MHI’s innovations such as the MALS air lubrication system and a ballast water treatment system. Leveraging these and other advanced technologies, MHI is actively promoting its engineering business for both new ships and conversion of existing ships. In line with that initiative, the company established, on 1 January, a new ‘engineering business department’ within its shipbuilding and ocean development business headquarters.

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