SWATH is an acronym that stands for 'Small Waterplane Area Twin Hull'. Seen from above the waterline, the vessel looks very similar to a traditional catamaran. This hull design places most of the hulls volume beneath the surface and the relatively thin hull members that make up the waterplane remain fairly unaffected by the wave action. This same concept is seen on semi-submersible offshore platforms to keep wave induced motions to a minimum.
The SWATH concept was invented in 1938 by Fredrick G. Reed and patented in 1946. The first vessels to be built using this technology came about in the late 1960's.
Although the small waterplane area provides less wavemaking resistance than a traditional vessel, the increased wetted surface area means that a large increase in power is required to propel the vessel when compared to a similar sized vessel of traditional hull design.