Finer hulls are more efficient at high speeds but as weve just seen suffer from more WSA and so for normal cruising catamarans in average conditions a ratio of 111 - 131 seems optimum.

Catamaran hull beam. It is a geometry-stabilized craft deriving its stability from its wide beam rather than from a ballasted keel as with a monohull boat. Excessive beam will reduce the fore and aft stability. Resistance curves of equal weight vessels having different hull fineness-ratios show how the resistance wall at about 24 knots impedes wide bodied 31 bl beamlength ratio hulls and actually prevents them from accelerating further.

Slender hulls such as 161 and even 121 bl ratio vessels are hardly affected by this imaginary barrier. However this drag formula is generally not the limiting factor for catamaran hull speed. A catamaran ˌkætəməˈræn informally a cat is a multi-hulled watercraft featuring two parallel hulls of equal size.

Typically this will be 8-101 for a slow cruising catamaran or the main hull of most trimarans 12-141 for a performance cruiser and 201 for an extreme racer. An improved twin hull vessel of the catamaran type having a central bridgedeck and a pair of side hulls interconnected by lateral suspension arms. Hull length-to-beam ratio LwlBh This ratio is the measure of hull slimness at the waterline which is significant for performance.

Indeed its extremely rare for beams to break off the hulls. The Prismatic Coefficient Cp is a measure of the fullness of the ends of a boat the higher the number the fatter the ends and - surprisingly - the more efficient at high speeds. In the case of a catamaran which has no keel to weigh the boat down slimmer and more hydro dynamically optimized hulls this theoretical hull speed rarely applies.

Lengthbeam ratio of the catamaran LBRC is defined as follows. Usually the waterline dimensions LWL and BWL are used for monohulls or for a single hull of a multihull. Good catamaran cruisers have values from 8-12 racers from 12 to significantly higher.

If we set LBRC 22 the longitudinal and transversal stability will come very near to the same value. We still need to determine the beam of one hull B H1 Figure 4. B H1 must be bigger than B WL of the hull.