The original design of the ACV, with a large air clearance between vehicle and surface (the "peripheral jet"), required too much power. It has been superseded by a skirted or trunked ACV, in which almost all the clearance is provided by the flexibility of a tough nylon skirt, covered with an elastic substance such as nitrile rubber. A fan pumps air into the air cushion to counteract the constant leakage under the lower edge of the nylon skirt. Propulsion is provided by one or more variable-pitch propellers.
Another form is the "side-wall" ACV (sometimes referred to as the CAB, or captured air bubble), which has sides extending into the water. It may be used when low speeds are needed and when the operation is not amphibious or not in shallow water.
The first ACV was operated in 1959. Development since then has been very rapid. A typical small ACV weighs about 8 tons and can carry 15 passengers or 31/2 tons of cargo. It may speed along at 60 miles (100 km) per hour and maintain this speed in waves 3 feet (1 meter) high or may operate at reduced speeds in waves 8 feet (2.5 meters) high. Other plans for ACVs include surface effect ships (SES) of 5,000 to 30,000 tons, capable of crossing the oceans at speeds ranging from 70 to 115 miles (110 to 180 km) per hour.
