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What is SWATH?

The SWATH acronym stands for Small Water Plane Area Twin Hull. It refers to a relatively new ship type that can greatly reduce or eliminate passenger seasickness while increasing crew effectiveness and safety. A well-designed SWATH ship rides through a seaway without the large motions and accelerations of conventional vessels.

A primary cause of seasickness is the periodic vertical accelerations of traditional ships in a seaway. By canceling out wave forces that cause large motions and accelerations, a SWATH ship can offer a level of passenger comfort unattainable on a monohull or catamaran of similar size.

The general configuration of a SWATH includes two lower hulls, vertical struts, and a cross structure. Typical variations are shown in Figure 1.
Figure 1: General configuration of a SWATH
Figure 1: General Configuration of a SWATH

Most of the displacement of a SWATH vessel is in its lower hulls; they remain below the waterline and contribute to the stability and small motions of the vessel in waves. The vertical struts connect lower hull to cross structure and provide the waterplane area required for stability. The sponsons or haunches carry the transverse loads to the cross structure and provide reserve buoyancy. The cross structure carries the payload and gives clearance for wave passage between the struts. The wet deck is the lower surface of the cross structure.

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