The first hovercrafts appeared in the 1950s. As time went by it became clear that they had a great deal of drawbacks along with the advantages. Shipbuilders launched onto the next idea of air (gas) cavern crafts. This technology involves the same air cushion designed differently. In the traditional air cushion air (or exhaust gases) is pumped under the bottom of the vessel thus lifting the vessel, which is then launched forward. Air cavern vessels also have air pumped under the bottom, but the sequence of the process is different. The vessel starts moving and gains speed and only then an air cavern is formed under it due to the sponsons or steps. The vessel is never fully lifted above the water surface, as the stern and the engines remain in the water.
First such vessels appeared in the 1970s and have been constantly improved ever since. Physicists from Nizhny Novgorod have proposed one of such new improvements. The idea is the following: if in order to create a gas cavern exhaust pipes are brought out to the vessel bottom, why not place the engine nozzles there as well to burn the fuel (gas) under the vessel bottom as well? Calculations show that such design will provide additional capabilities to increase the cavern area and thus reduce the friction. But that’s not the whole story. The effect of combustion products expansion will create additional thrust. One just has to install a cascade of transverse sponsons to capture the expanding combustion products. Jet streams will hit the sponsons and propel the vessel forward.
Modeling in a laboratory pool as well as the calculations show that this design can work for real vessels and is sufficient to provide movement at the current speed range. In other words, scientists from Nizhny Novgorod proposed a radically new type of vessel engines.