"SWATH gives a craft the ability to deliver big-ship platform steadiness and ride quality in a smaller vessel and the capability to sustain a high proportion of its normal cruising speed in rough head seas. The waterplane is the horizontal-plane cross-section of a ship's hull at the water surface. Thus, the boat has two submarinelike lower hulls completely submerged below the surface; above the surface it resembles a catamaran. Ship motions are caused by the waves on the ocean surface, which produce forces on the hull that decrease rapidly as the hull is moved farther below the surface, as with a submarine. Wave-exciting forces can also be made smaller if the amount of waterplane area at the design waterline is decreased. However, the objective of SWATH is not to minimize ship motions at the expense of speed/power or payload capabilities. Instead, the relative proportions for the strut waterplane area and submerged hulls are selected to reduce motions and accelerations well below accepted criteria for seasickness or onset of degraded performance of personnel or equipment. All SWATH crafts will have less than 50 percent as much waterplane area as a monohull of equal displacement."