buoyancy of a SWATH ship is provided by two submarine hulls
connected to the upper platform by twin narrow struts from each of the
submarine hulls. This mature technology is used by the military and for
deep-sea research ships. Until now, it has not been available in a
private yacht. Very simply the hull form reduces the upward forces on
the vessel as the wave passes through. The biggest advantage comes in a
beam sea because the technology significantly reduces the vesselís
vertical movement and totally eliminates the quick jarring
The idea of SWATH was taken from the principle of submarines at periscope depth, which has been shown to have minimal or no motion, placing most of the ship's displacement under the waves.
The Small Waterplane Area Twin Hull (SWATH) is a twin-hull ship design that minimizes hull volume in the surface area of the sea. By minimizing hull volume in the sea's surface, where wave energy is located, the vessel becomes very stable, 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, as wave excitation drops exponentially with depth.
(1) the ability to deliver big-ship platform steadiness and ride quality in a smaller vessel and
(2) the ability to sustain a high proportion of its normal cruising speed in rough head seas.
SWATH ships typically have two submarine-like lower hulls completely submerged below the water surface. Above water, a SWATH resembles a catamaran.
However, the purpose for a balanced Small Waterplane Twin Hull ship design is NOT to minimize ship motions at the expense of speed-power or payload capabilities. During the design process, if the total amount of strut waterplane area is decreased, the transverse spacing between the hulls must be increased to regain adequate transverse stability to resist heeling over moments as a result of wind or movement of all passengers to one side of the ship.
Adequate clearance to the underside of the connecting structure is also essential to allow the Small Waterplane Twin Hull ship to ride over surface waves that are typically present in coastal waters. This type of operating mode results in the smallest vertical motions and is called platforming. For rough seas, with wave heights exceeding the amount of cross-structure clearance, SWATH ships are designed to have a sufficiently short heave period to provide inherent contouring behavior at low speeds.
A little history,
Frederick G. Creed, a Canadian, presents his idea for a
small-waterplane-area twin-hull aircraft carrier to the British
Admiralty. Several years later Creed is permitted to show it to the
U.S. Navy, but they do not pursue the concept.
Frederick Creed is awarded a British patent.
1959 - U.S.
Navy activity in moderately high speed "semi-submerged ships" begins
with H. Boericke proposing the streamlined "shark form" monohull for
which he was awarded a patent in 1962.
1965 - Alan
McClure of Houston proposes the MOHOLE platform, with a configuration
similar to Blair's, as a mobile drilling rig.
1967 - Dr.
Reuven Leopold of Litton Industries presents to the U.S. Navy his
moderately high speed TRISEC concept2, for which he was awarded a
patent in June, 1969.
1968 - The
40m long, low speed small-waterplane-area twin-hull vessel Duplus3 is
launched by the Boele Shipyard in the Netherlands. Designer of the
1200-ton Duplus is a Dutch naval constructor, J. J. Stenger, who based
his design for a self-propelled oil exploration support vessel on the
fact that submarines lying at periscope depth experience little
1968 - an
M.I.T. student proposes a streamlined version of the MOHOLE platform
for a class project and carries out model tests on the design, which he
called a semi-submerged catamaran.
1968 - Dr.
Tom Lang of the Naval Underseas Center (NUC) in San Diego begins
intensive development of his concept for a "high speed ship with semi-
submerged hulls", for which he was awarded a U.S. patent in 1971. A key
element of the concept is the provision of movable horizontal fins
located aft of the vessel's center of gravity to stabilize vessel trim
and pitch motions at higher speeds.
Mitsui Engineering & Shipbuilding Co., in Tokyo, begins basic
research on the "semi-submerged catamaran", or SSC.
Construction begins on the 190-ton SWATH workboat SSP KAIMALINO for NUC
after 18 months of research by engineers at NUC and nearly 2.5 years of
design and confirmatory model testing. Launching occurs in March,
acronym "SWATH" is coined by U. S. Navy technocrats who promote its
use, rather than "semi-submerged" ship or catamaran, to distinguish
this concept from conventional catamarans.
Mitsui Engineering & Shipbuilding completes the world's first
commercial SWATH ferry, the 26.5 knot MESA 80 (aka, SEAGULL), with a
capacity of 446 passengers.
1991 - The
first of a class of 4 SWATH acoustic Surveillance ships designed by the
U.S. Navy, the 71.5 m long victorious, is delivered to the Military
Finnyards delivers the first SWATH cruiseliner, the 131 m long Radisson
Diamond, to Diamond Cruise Ltd.
1993 - The
existence of the world's first so-called "stealth" ship, the U.S.
Navy's 50 m long Sea Shadow, an A-Frame SWATH ship built by Lockheed
Missiles and Aerospace Co., is declassified and disclosed publicly,
leading to a cover article in the July '93 issue of Popular Mechanics.
1. Boericke, H., Jr., "Unusual Displacement Hull Forms for High Speed,"
International Shipbuilding Progress, Vol. 6 (1959).
2. Leopold, R., "A New Hull Form for High-Speed Volume-Limited
Displacement-Type Ships," Paper No. 8, Society of Naval Architects and
Marine Engineers Spring Mtg. (May 1969).
3. Stenger, T.T., "The Trident Stabilized Vessel Concept for Offshore
Drilling and Construction Operations," Offshore Technology Conference,
Paper OTC 1138 (1969).
4. Lang, T.G.; Hightower, J.D.; Strickland, A.T.; "Design and
Development of the 190- Ton Stable Semi-Submerged Platform (SSP)," ASME
Paper No. 73-WA/OCT-2 (Nov. 1973).
5. "Mesa 80: Mitsui's Semi-Submersible Catamaran as a Fast Ferry," The
Motor Ship, (July 1980).
6. "America's Invisible Warship," Abe Dane, Popular Mechanics, (July