SMALL WATERPLAN AREA TWIN HULL (SWATH)

The Small Waterplane Area Twin Hull (SWATH) is a hull form used for vessels that require a ship of a certain size to handle in rough seas as well as a much larger vessel. An added benefit is a high proportion of deck area for their displacement — in other words, large without being heavy. 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. It was first used in the 1960s and 1970s as an evolution of catamaran design for use as oceanographic research vessels or submarine rescue ships.

Catamarans provide large, broad decks, but have much higher water resistance than monohulls of comparable size. To reduce some of that resistance (the part that generates waves), as much displacement volume as possible is moved to the lower hull and the waterline cross-section is narrowed sharply, creating the distinctive pair of bulbous hulls below the waterline and the narrow struts supporting the upper hull.

Swath designs are more expensive to produce than conventional twin hulled vessels.  The advantage to such a design is that a significant proportion of the hull remains below the surface of the sea.  For this reason wave contact is reduced where it may only act on the thin leg areas.  Wave drag is a major component of the total drag on a vessels hull.  For this reason the hull is more stable, being less prone to pitching and rolling and requires less power for propulsion than conventional designs.    

A Swath design wastes proportionally less energy climbing wave peaks and accelerating down troughs.  The passage is smoother.  The below surface hull (in normal operating conditions) is subject to laminar (or pipe) friction, which is more predictable.  The SSC Radisson Diamond is an example of a commercial ocean liner claiming to offer unrivaled cruise comfort

solarnavigator.net
lovelymimiko@blogspot.com