Diving into uncharted waters

The world’s first fuel cell-powered submarine is currently undergoing deep-water trials and will enter service with the German navy in August.

The 56m long, 11.5m high class 212A submarine, manufactured at the Kiel shipyard of German company Howaldtswerke-Deutsche Werf, is powered by a hybrid propulsion system consisting of a diesel generator with a lead acid battery, and an air-independent propulsion system (AIP) based on nine Siemens proton exchange membrane (PEM) fuel cells. These produce electrical energy from oxygen and hydrogen and provide between 30 and 50kW each.

The hydrogen for the cells is stored in metal hydride cylinders —where hydrogen is chemically bound to the metal. This is not only safer than storing gaseous or liquid hydrogen onboard a U-boat, but it also enables much more hydrogen to be stored in a small space, keeping the submarine as compact as possible, according to HDW spokesman Dr Jürgen Rohweder.

In typical operating conditions the lead acid battery is powered by the generator and used for higher speeds, while the fuel cell system can be used for stealthier operations and can power the sub for weeks without having to surface.

The beauty of a fuel cell propulsion system is that it enables a vessel to remain undetected underwater for weeks at a time. ‘It is absolutely quiet because it relies on a chemical process and produces hardly any heat, so the vessel cannot be detected via sonar, noise or infrared,’ claimed Rohweder. The other big advantage is the cell’s high net efficiency: around 70 per cent.

Rohweder said that while fuel-cell subs have many advantages of their nuclear equivalent – low signature, and undetectability – the technology is not seen as a replacement, but rather as a new option for U-boats designed for use in coastal areas. He added that while the cell is quieter and smaller than a nuclear power unit it does not allow the vessel to remain submerged for as long.

‘The fuel cell submarine fills the gap between conventional diesel-electric submarines and nuclear vessels,’ he said.

Ultimately, the boat’s extremely low signature will probably see it replace diesel-electric systems, he said, citing the huge amount of interest from 30 different navies.

HDW is currently building three more 212A-class U-boats for the German navy, while two Italian boats of the same class, also built by HDW, are expected to enter service in 2005. The company is also in the process of building four 214-type fuel cell submarines; one is being built in Kiel, one in Scaramanga, Greece and two in Korea.

The fuel cells can also be retrofitted to some existing U-boats, and HDW recently received an order from the Greek navy to upgrade three of its 209-class submarines.

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