Uplifting experience

French naval architects are finalising the design of a radical super-fast vessel that will feature a new kind of engine air intake.

Marseilles-based design shop Bureau d’Etudes Gilles Vaton Innovation (BGV) has revealed proposals for a high-speed trimaran for civilian and military applications. Instead of conventional air intakes for its gas turbine engines, a system of ‘microholes’ will be used in the two winglets on either side of the main hull. These will take up less space and make the ship more stealthy and aerodynamic.

Gas turbine engines used in ships to turn the propeller or provide the energy for electric propulsion require large air intakes which take up great amounts of space on the deck and within the vessel, and, of concern to the military, can increase the ship’s radar or infrared signature.

BGV’s marketing manager Christian Gautier said the winglet design involves thousands of 3mm microholes into which the air would pass.

These would be positioned in narrow strips about a third of the way along the upper surface of the winglets. Here the airflow would be faster because of the aerofoil effect.

With the microhole system, less salt and spray should get into the holes than in a normal intake, said Gautier. Using holes in the wing would also help reduce the craft’s signature. BGV is registering a worldwide patent for the technique, known as ‘boundary layer aspiration’.

To boost efficiency the BGV design will also exploit the ‘ground effect’ (see sidebar), cancelling out some of the vessel’s displacement with the lift created by the winglets. The smaller versions of the BGV concept, ranging from 53m to 75m long, will be powered by German-built MTU diesel engines, while the largest design, the BGV120, will be fitted with Rolls-Royce MT30 marine gas turbines and Kamewa waterjets. Based on the Trent engine that powers the Airbus A330 and Boeing 777 airliners, the MT30 was designed specifically for the marine market.

Another option for BGV is the WR-21, the engine that will power the Royal Navy’s new Type 45 destroyers and future aircraft carriers.

Built by UK, US and French companies including Rolls-Royce and Northrop Grumman, the WR-21 features an intercooler and recuperator device to redirect excess heat from the turbine exhaust back into the engine cycle, enabling efficiency gains.

Gautier said that although no contract had been signed, navies, including the French and US, were showing considerable interest in the BGV design.

Sidebar: ground effect

The BGV’s average cruising speed in choppy conditions would be around 50mph.The concept exploits the ‘ground effect’, an aerodynamic phenomenon that reduces turbulence around a wing as it flies just above the relatively flat surface of an expanse of water. Reducing turbulence lowers drag on the wing, which in turn allows it to create lift much more efficiently.

In the BGV the ground effect created by the winglets between the main hull and the outriggers on either side can cancel out as much as 15-20 per cent of the vessel’s displacement, according to BGV’s Christian Gautier.

By using an efficient method of lifting the boat partially out of the water, Gilles Vaton engineers believe the BGV120 could reach speeds of up to 180mph, a bold claim considering that few naval vessels can exceed 40mph. Even the Joint Venture, an Australian catamaran under trials with the US military, travels at only 45mph.

Moreover, the BGV’s 9m-high aircraft-style fin would also enhance its speed, said Gautier. While its main purpose is to act as a mast, raising electronic sensors above the deck for a clearer line of sight, the fin could also behave like a sail in a crosswind to augment the propulsion system.

Up to 50 engineers have worked on the project since 1997, and preliminary tank tests of models took place 12 months ago. In the last couple of months the bureau finished designing two military aviation-related configurations.

The main military versions are intended to carry over 1,500 marines or six helicopters. Civilian versions would include fast ferries or container ships with a range of about 5,600 miles.

The Russian military has been experimenting with ground effect surface-skimming aircraft known as Ekranoplans since the 1950s. Earlier this year Boeing’s Phantom Works R&D centre revealed a super-heavy transport aircraft concept, the Pelican, also designed to exploit ground effect .