Blasting air under a vessel’s hull can cut its fuel consumption
Bubbles are wont to slip past the edges of even flat hulls, but efforts to hold them in place are paying off, says Uwe Hollenbach of the Hamburg Ship Model Basin, a facility that tests new naval technologies. One trick is to trap the blanket of air between two ridges that protrude a few centimetres downward from the port and starboard edges of the hull. Another is to shape the vessel’s stern in a way that stops air being sucked into the propeller, where it would reduce thrust by lessening the propeller’s grip on the water. It is even possible to design hulls that include air-trapping recesses a couple of metres deep.
Damen Shipyards Group, a Dutch firm that builds more than 150 ships a year, has found that such cavities cut fuel consumption by about 15% on a 60-metre test ship that carries cargo on rivers. Tests at MARIN, a naval-engineering institute based in Wageningen, also in the Netherlands, suggest air cavities can cut a big ship’s fuel costs by as much as 20%. Damen, meanwhile, estimates that the air-lubrication system will increase the cost of building a 110-metre cargo ship by only about 5%. It expects production to begin early next year, and plans to license designs to other shipbuilders soon thereafter.