Airmax prototype demonstrator gets airborne

The Swedish shipping company Stena Bulk will invest in the region of SEK 50 million ($7 million) in the project. Following the very good results achieved in tests with small ship models, Stena Teknik has developed this large-scale model weighing 25 tonnes. The same tests will now be carried out with the Stena Airmax.

Five years ago, Stena Teknik initiated a development project in order to find a method of reducing a ship’s water resistance, thus radically reducing energy utilisation and fuel consumption of large tankers in the future. “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”, says Ulf G. Ryder, president and ceo of Stena Bulk.

Stena Teknik has co-operated with Chalmers University of Technology and SSPA in Gothenburg in the development project and the construction of the P-MAXair model. The Stena Airmax will be tested in the Gullmars Fjord on the Swedish west coast, during spring 2010 when extensive test-programmes will be run. The model will be powered by electric motors during these simulations.

Air cushion reduces friction

The concept involves reducing the ‘wet surface’, i.e. the part of the hull that is in contact with the water which creates friction and slows down the ship. This is achieved by means of a cavity filled with air in the bottom of the hull. This means that the water is in contact with air instead of steel plate, thus reducing friction. This may seem simple, but a number of phenomena complicate the picture. These include internal wave formation in the cavity, which reduces the positive effect. A balance must also be struck between optimising the air pressure to achieve the greatest possible reduction in resistance and, at the same time, minimising air leakage.

The effect of air in full scale

Testing ship models in test basins has a long history and the technique of scaling up the results from a model to an actual ship is well known. However, Stena’s project is different in that air is also involved. There is no previous experience of the effect of the air when a model is scaled up to full scale. Building a ship based on normal model tests of a 4m long model would have been very risky.

Accordingly, Stena decided to build a 1:12 model, i.e. a 15m long model, to verify that the results achieved also applied on a larger scale. This has never been done before and testing the air regulation system will also be an important part of a future project.

Stena has applied for a patent for the wide and flat bulbous bow, which facilitates a favourable water flow below the hull.

Technical data for the Demonstrator model Stena AirMAX on a 1:12 scale
Length 15m
Breadth 3.3m
Draught ‘fully loaded’ 0.9m
Weight fully loaded 35 tonnes
Speed 5 knots
Propulsion 2 x 10kW

Full scale size of Stena AirMAX product tanker:
Length 182m
Breadth 40m
Draught ‘fully loaded’ 11.3m
Weight ‘fully loaded’ 65,000 tonnes
Speed 14 knots
Propulsion 2 x 8,000kW

The model consists of a steel box, containing all the equipment, surrounded by a hull made of fibreglass reinforced plastic. The flat bottom has a cavity for an ‘air cushion’, which is almost as wide and half as long as the ship.

The model is powered by two 10kW electric engines with electricity provided by a diesel generator. The air cavity is fed with air by fans and the air is controlled so that the bottom of the air cushion is in line with the bottom of the hull.

The model will be manned by 1-2 persons and test data is transmitted via a link to a tender boat. Personnel and boats from the Swedish Sea Rescue Society will assist during the tests.