Aerodynamic support could give fast patrol unit speed of 50knots

by | 13th March 2018 | News

Home News Aerodynamic support could give fast patrol unit speed of 50knots

Warship Technology: March 2018Advanced Hull forms

Late February 2018 was due to see the first example of a new type of vessel with a unique hull shape and mode of operation enter operation servicing oil production facilities in Gabon in West Africa.
The vessel, Clémentine, was built for Peschaud International in France, and will be used to transport 25 oilfield technicians to inland oil production facilities. Clémentine completed sea trials early in 2018 and has a service speed of 40knots with two 600hp diesel engines.


The A2V-25-CB is the first production version of a new vessel that shares some of the characteristics of a surface effect ship (SES) and those of a wing-in-ground effect vessel (WIG) of the type that was developed by the former Soviet Navy, but differs from them in a number
of respects.


Other applications
The first A2V vessel will be used to transport personnel on rivers along the Gabonese coast, but another, larger unit also designed by the French company is suitable for use offshore. So too is a military/paramilitary/coast guard version of the same hull type, the A2V-Fast Patrol.


A2V naval architect/R&D engineer Gianluca Guelfi explained that the new hullform that the company has developed has very much lower fuel consumption than a conventional vessel thanks to its unique design,
in which the vessel is partially lifted out of the water somewhat in the manner of a surface effect ship (SES).


However, the key difference between the A2V vessel and a SES is that the latter uses blowers to produce lift, whereas the A2V concept uses aerodynamic lift to raise the vessel, in the manner of an aerofoil. Therein lies its reduced hydrodynamic drag, and ability to reach high speeds with lower levels of fuel consumption and emissions than a conventional craft, transferring personnel over long distances in a shorter time period than would otherwise be possible. Other benefits of the concept – which uses business class seating – include reduced noise levels.


Twice the speed, half the fuel
The A2V aerodynamic lift concept was tested using a number of prototypes in 2015-2016. The company continues to work with classification society DNV GL to obtain approval in principle for other, similar applications that would make use of the design’s ability to, as Guelfi put it, to safely transfer the weight of the vessel “from water to air.”


“Reducing the weight of the vessel is the key to greater efficiency,” said Guelfi. “With A2V you get twice the speed for half the fuel. Thanks to aerodynamic support, above a critical speed, the faster A2V vessels go the less fuel they use.”


This critical speed depends on the application and size of the vessel but the fuel economy with respect to conventional boats is, said Guelfi, “very significant” above 25knots. This is, he noted, in contrast to conventional high-speed vessels in which oversized engines allow incremental speed improvements at the cost of much higher fuel consumption and reduced payload, leading to what he described as “economically and environmentally unsustainable costs per passenger.”


As highlighted above, A2V’s hull concept is similar in some respects to a WIG, but a WIG can actually take to the air because – at some speeds – aerodynamic lift is sufficient for it to take flight (above the water). In contrast, in the A2V aerodynamic lift ‘alleviates’ hydrodynamic drag but the unit remains a vessel at all times. The A2V achieves this with the use of propellers or waterjet propulsors and diesel engines, whereas a WIG would usually use gas turbines.


The French company’s catamaran configuration provides greater lift than an equivalent WIG wing because the two hulls act like winglets (or wingtip devices) and prevent the formation of wingtip vortices, and Guelfi said this improves efficiency and total lift produced by the cross deck.


The A2V-Fast Patrol would have a range of 700nm. It would be suitable for patrol, surveillance, border protection and search and rescue and is also suitable for use in shallow water.


With a length overall of 11.95m and breadth of 7.35m, the A2V Fast Patrol would have an air draught of 3.85m, draught of 0.55m, and a cruising speed of 50knots at 90% MCR. It maximum speed would be 60knots.
Built in fibre-reinforced plastic, it would have a pair of 230kW main engines (such as Yanmar 8LV-350s) and surface-piercing propellers, along with a small diesel generator.

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