Counter blast

A blast-resistant hull structure designed to protect ships from terrorist attack is being developed by UK researchers for the US Navy.

The hull, using strong but lightweight lattice material, is being designed in response to the Al-Qaeda bomb attack on the USS Cole in 2000, which killed 17 crew, said Dr. Vikram Deshpande, a researcher at Cambridge University’s engineering department. When a bomb explodes near a ship, the hull completely fractures, he said. ’The Cole prompted the US Navy to start thinking: if someone comes up beside a ship and detonates a small bomb, how do we stop the hull tearing?’

The design is based on a sandwich structure. Many US Navy ships have a double hull, consisting of two steel skins with an air gap in between, but these are not strong enough to withstand a blast. The sandwich hull is based on this design, but contains a trellis-style structure between the two skins.

’Sandwich structures are very good at bending, and structures that give are always strong. But you also need to have a strong core, so it doesn’t shear off under the load. This is where the lattice structure comes in,’ said Deshpande.

Lattice materials, the brainchild of Deshpande and his colleague Prof. Norman Fleck, were originally conceived as a new structure for aircraft wings. The lattice is built up on the principles of triangulation and is similar in design to the large trusses used for bridges and airport ceilings. The structures are made by cutting patterns from steel sheets, and folding them into shape.

Lattice materials are very strong, without adding much extra weight to a ship, and are also cost effective, said Deshpande. ’You could make hulls more blast resistant by using fancy materials, but it simply increases the cost.’

The research is still at an early stage, and the team is investigating how the structure will respond to the massive force applied to it by a bomb blast. He said it would also strengthen the hull against collisions, such as when HMS Nottingham grounded off Lord Howe island earlier this year.

The work is part of a two-year project, funded by the US Office of Naval Research’s international field office in London, and is due for completion in 2004.

Hulls based on sandwich structures are expected to be more resistant to corrosion and better at absorbing sound than existing materials. Lattice materials have good heat-transfer characteristics, allowing them to be used as heat exchangers and for cooling electronic components.