Small-waterplane-area twin hull

A small waterplane area twin hull, better known by the acronym SWATH, is a catamaran design that minimizes hull cross section area at the sea's surface. Minimizing the ship's volume near the surface area of the sea, where wave energy is located, minimizes a vessel's response to sea state, even in high seas and at high speeds. The bulk of the displacement necessary to keep the ship afloat is located beneath the waves, where it is less affected by wave action. Wave excitation drops exponentially as depth increases, so wave action normally does not affect a submerged submarine at all. Placing the majority of a ship's displacement under the waves is similar in concept to creating a ship that rides atop twin submarines.

A narrow waterline distinguishes a SWATH ship from a conventional catamaran
A SWATH ship resembles a conventional catamaran. The twin hulls (blue) remain completely submerged.

Effects

The twin-hull design provides a stable platform and large, broad decks. Compared with conventional catamarans, SWATH vessels have more surface drag, but less wave drag. They are less susceptible to wave motion but more sensitive to payload, which affects draught. Additionally, SWATH vessels cannot operate in planing or semi-planing modes and thus gain no drag reduction when operating at speeds normally associated with such modes.[1] They require a complex control system, have a deeper draft, and have higher maintenance requirements. The design of SWATH vessels is also considerably more complex due to the structural complexities inherent to the design.[2]

History

The SWATH form was invented by Canadian Frederick G. Creed, who presented his idea in 1938, and was later awarded a British patent for it in 1946. The first full-scale SWATH vessel to be built and put into service was MV Duplus,[3] a diving support vessel built in the Netherlands in 1968. In the 1970s, several units were built in different countries (including the RV Kaimalino by the US Navy,[4] and an 80 ft (24 m) ferry in Japan). Since the 1980s, oceanographic research vessels, pilot tenders, yachts and other craft are more routinely being built with the SWATH hull type.[5]

Specific examples
German Navy research ship Planet
German Federal Coast Guard customs cruiser Helgoland

See also
  • Multihull – Ship or boat with more than one hull
  • M80 Stiletto – Prototype naval stealth vessel
  • Catamaran – Watercraft with two parallel hulls of equal size
  • Sea Slice – Experimental SWATH vessel, an experimental US Navy ship with multiple SWATH hulls.
  • Semi-submersible – type of vessel which can partially submerge
  • Trimaran – Multihull boat
  • Wave-piercing hull – Hull with fine bow with reduced reserve buoyancy

References
  1. Misra, Suresh Chandra (2015). Design Principles of Ships and Marine Structures. CRC Press. p. 474. ISBN 9781482254471.
  2. Busch, Ian Richard (1990), On the Cost Effectivelness of Large Commercial SWATH Vessels, Cambridge: Massachusetts Institute of Technology, Department of Ocean Engineering, p. 418
  3. "Boele-Bolnes launch twin-hull craft for offshore work". Holland Shipbuilding. 17 (9): 58. 1968.
  4. LaPuzza, Tom (March 2005). "SSC San Diego Command History Calendar Year 2004" (PDF). United States Navy SSC SAN DIEGO. Archived (PDF) from the original on February 28, 2017.
  5. Arps, Jan L. (May 1973). "The Role of the Semi-Submersible Work Vessel In Offshore Production Operations". Fifth Annual Offshore Technology Conference. Offshore Technology Conference. doi:10.4043/1867-MS. ISBN 978-1-55563-659-3.
  6. "AOS Hibiki Class". GlobalSecurity.org. Archived from the original on September 5, 2009.
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