A hovercraft is a vessel that benefits from a aerostatic force. The aerostatic force is generated by a current of air going down that creates an air cushion beneath the craft of which there are three types:
1. Open Plenum
The air is held in the hollow region underneath the craft(=plenum chamber) and goes out around the periphery.
2. Peripheral Jet
The air is pumped underneath the vessel through a narrow slot going entirely around the circumference, the air will go towards the center of the vessel, forming an external cover that would successfully contain the cushion. Once there is air gathered below the craft to a pressure that is equal to the weight the incoming air has nowhere to go but outwards.
In contrast to the open plenum the momentum of the peripheral jet air keeps the cushion pressure and the ground gap higher.
3. Flexible Skirt
These hovercrafts are not amphibious, nevertheless it has many of the advantages of a true hovercraft. In this case the side walls of the hovercraft are extended into the water for a high degree of lateral stability. The front and the back of the craft remains sealed by the skirt so it can contain the air cushion. Sea friction is of course much reduced although there is some increase in the air resistance and an addition due to the dipping skirt. An evolved design of the flexible skirt is the moving “fingers” attached to the bottom that maintains the airflow more efficiently.
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