Air trap coating cuts boats’ barnacle bills

With help from a thin cushion of air, Scottish chartered engineer Ian Stark has invented a novel way to protect boat hulls from marine fouling which costs an estimated £15bn a year to remove. Just six month’s barnacle build-up on a super tanker, for example, increases the energy needed to drive it by 40%, to […]

With help from a thin cushion of air, Scottish chartered engineer Ian Stark has invented a novel way to protect boat hulls from marine fouling which costs an estimated £15bn a year to remove.

Just six month’s barnacle build-up on a super tanker, for example, increases the energy needed to drive it by 40%, to compensate for friction losses between the roughened surface of the hull and the sea water.

Other anti-fouling coatings are more or less toxic and some, like those based on tributyl tin, are banned by some countries because the chemicals can kill whales. Invariably these coatings peel off and have to be renewed at great expense – a tanker in dry dock costs £120,000 a day.

Stark’s anti-fouling coating works by trapping a thin film of air between the boat hull and the seawater to prevent marine growth. The air also provides an extremely smooth, near friction-free, surface.

He illustrates the concept by describing the dish-shaped meniscus which forms on the surface of a tumbler of water.

In the case of a boat, surface tension traps air with great force against the hull which has been sprayed with a special coating, just microns thick. The coating is made from a jelly-like suspension of silica which, being hydrophobic, repels the seawater.

The difficult part has been to get the inert and lightweight silica to stick to a standard two-part epoxy coating normally used to protect the hull from metal corrosion.

Apart from boats, industrial applications could include development of more energy-efficient pumped systems where the coating is used to line pipes to reduce turbulence and increase laminar flow.

Protective Research Industries, the company set up to develop coatings based on the technology, has applied for international patents.

But Stark says more work needs to be done before putting it on the market.