The VariSWATH design variant overcomes some operational limitations of more conventional SWATH vessels that operate only with lower hulls completely submerged.  The SWATH vessels are designed with circular hull cross-sections and have deep draft relative to equivalent monohulls.  Seakeeping characteristics deteriorate as speed of a SWATH vessel decreases.  Deep draft of conventional SWATH frequently limits operating area, harbor/estuary access, and pierside berthing options.  The VariSWATH design is a variable draft concept with a nearly rectangular hull cross-section.  This variation allows for matching draft to sea conditions, permitting more efficient transits in favorable weather with the hulls only partially submerged, and providing steadier operation at slow speeds in heavy seas with the hulls fully submerged.  The rectangular hull cross-section, which is not practical in a traditional SWATH, greatly reduces the amount of vessel motion in a seaway when operating fully submerged at slow to moderate speed or holding station.  The vertical strut arrangement and hull form makes ship motion nearly independent of heading relative to wave direction.  The variable draft capability gives flexibility for a wide range of payload versus draft and speed options.

Distinguishing features of VariSWATH design technology are outlined below.

  • Variable draft to maximize speed at transit draft, steadiness at deep draft, and survivability at intermediate draft.
  • Steadiness at transit draft is superior to equivalent monohulls.
  • Steadiness at deep draft is superior to equivalent conventional SWATH.
  • Less motion response (pitch, heave, and roll) than for a conventional SWATH when the vessels are not underway in a seaway.
  • Minimal change of total motion response in a seaway as ship heading changes relative to wave direction.
  • Full load transit draft generally about the same as comparable monohulls.
  • Calm water cruise speed equal to or better than comparable monohulls.
  • Cruise speed in a seaway better than comparable monohulls.
  • Capability to adjust trim at least ±5 degrees under all operating conditions when loitering or on station.
  • Capability for overload (fuel and/or payload in excess of design full load) which increases draft and reduces maximum speed.