South Pacific islanders are credited with the original catamaran design, so it's not surprising cats have been widely accepted Down Under for years. But American anglers have been slower to embrace the style, though that is starting to change. Cat converts cite benefits like greater fuel efficiency with less power, improved stability and load capacity, a softer ride and shallower draft as reasons for making the switch from monohulls. More than a dozen companies in this country offer catamaran hulls that fall into three categories: full displacement, planing and semi-displacement. Each type has its own characteristics.