n advanced technology demonstrator, built  for  the  office of   Naval Research

(ONR) in the US, the AMH SeaCoaster, was christened at a ceremony at Austal's Mobile, Alabama shipyard, in the US in early October, and is due to start trials shortly.
   The 31.2m surface-effect catamaran will be used to demonstrate advanced hullform technology on behalf of the ONR, and is operated by American Marine Holdings, which has been awarded a contract to demonstrate the SeaCoaster design to ONR.
   The patented SeaCoaster catamaran design features cavities in the bottom of each hull into which air is blown providing lift to the vessel, reducing resistance, and thus allowing higher speeds to be obtained.
   Designer-inventor Don Burg expects the SeaCoaster to be capable of speeds up to 56 knots. Following its evaluation by ONR, American Marine Holdings expects various departments of the US military to consider using it for a wide range of applications.
   The SeaCoaster has a beam of 9.75m, hull depth (moulded) of 3.35m and is propelled by

a quartet of 1045W Catepillar diesel engines linked to four ZF Trimax surface-piercing propellers.
   The patent for the SeaCoaster hullform is held by Air Ride Inc in Miami in the US. Don Burg of Air Ride, who invented the hullform, has successfully applied it to a variety of craft, including a 65ft SeaCoaster catamaran ferry that remains in operation - Island Express Boat Lines has been operating a 149 passenger SeaCoaster ferry on Lake Erie since 1999.
   Originally developed with assistance from US Department of Energy Inventions and Innovation Program, the air-assisted catamaran has 'wave-slicing' fine entry sidehulls. The air cushions formed between the catmaran's sidehulls and the water surface support approximately 80 per cent of the vessel's displacement. Another advantage of the hullform concept is its reduced draft. The reduced wetted area resistance of the SeaCoaster reduces powering requirements by approximately 50 per cent compared with conventional catamarans and monohulls at cruise speeds.
   Taking into account the power required by the blowers, the SeaCoaster only requires around 60 per cent of the power of a standard catamaran, and the design has no flexible seals and no air cushions between the sidehulls, as is the case with Surface Effect Ships (SES). Air Ride says the SeaCoaster also has excellent platform stability without any of the 'cobblestone effect' experienced with some other hullforms.

Seacoaster general arrangement

WARSHIP TECHNOLOGY JANUARY 2005

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