Air Cushion May Reduce Tanker Energy Needs by 30 Percent

The Stena Airmax, a 35 ton tanker out of Gothenburg City, Sweden will be undergoing a series of tests to see if it will provide the energy savings that its model predicts. The 15 meter long model ship has been equipped with an air cushion that is said to reduce the friction between the hull and the water, potentially allowing for significant savings in fuel and emissions.

The organization responsible for the technology, Stena Teknik, started developing the technology over five years ago to find a method to reduce a ship’s water resistance. Since that time it has produced small-scale ship models of the design and conducted tests on these models. According to Ulf G. Ryder, President and CEO of Stena Bulk, one of the world’s leading tanker companies, “The results of the tests carried out are very promising. Depending on the type of ship and speed, we expect energy savings of 20-30 percent. This will now be verified in tests with the newly built prototype Stena Airmax”.

The wet surface, the metal surface of the ship that is in contact with the water, is considered a major cause of friction, which slows down a ship. Instead of metal in contact with the water, air within an air cushion is used. Such a design, in small-scale ship models, results in less friction between the hull and the water. And that’s because an air cushion, as part of the ship’s hull, is said to reduce the wet surface area of the hull.

Instead of metal, the model’s hull is made of fiberglass reinforced plastic. Additionally, the flat bottom of the ship has a cavity, about half as long as the ship and almost as wide. In that cavity is the air cushion. Air is fed into the air cushion, from fans, such that the air cushion is always in line with the bottom of the hull. One of the problems to overcome with the design is that the air pressure must be optimized in order to minimize the amount of friction between the hull and the water.

Although the company is optimistic about the outcome of the trials, there is concern that there isn’t any historical data that indicates that the positive effects of air cushioning will scale upward with a full-scale model. Because of this, Stena decided not to build a full-scale ship, even though initial model tests proved positive. Instead they opted to build a 1:12 model, the 15 meter long Stena Airmax. This new ship model has a breadth of 3.3 meters, a fully loaded weight of 35 tons, and a speed of 5 knots. The ship is powered by 2X10KW electric motors.

Chalmers University of Technology and SSPA, a ship design, maritime operation, port and coastal development services company that has tested over 6000 ship hull forms, have also been involved in the development project.

The full-scale ship, when built, will be 182 meters in length, have a breadth of 40 meters, a fully loaded weight of 65,000 tons and a speed of 14 knots. The full-scale ship will be powered with 2X8,000 kW electric motors.