The largest surface-effect currently in operation are two Russian 'Bora' class guided missile corvettes, which have a displacement of around 1,050 tonnes (2.31 million lb) and a claimed cruising speed of 54 knots (100 km/h or 62 mph). Similar to hovercraft, surface effect ships float on a fan-generated cushion of air, but their twin hulls never actually leave the water. The Bora are 65.6 m (215 ft) long, 18 m (59 ft) wide, and a full crew complement of 68. They are armed with eight Mosquito surface to surface missles, 20 anti-aircraft missiles, one 76.2 mm cannon, and two 30 mm gattling guns.Sea trials were conducted on the Baltic late in 1999. According to official sources these were successful, although independent commentators have questioned the seaworthiness and practicality of the vessels.Large fans under the ship create air pressure that gets trapped between the hulls and raises the ship, reducing the hull area that is actually submerged and allowing higher speeds and efficiency.See also 'Fastest warship' record: the US produced a smaller surface effect ship in the late 70s, but plans to create a 3,000 tonne version were scrapped.