Usually the waterline dimensions L WL and B WL are used for monohulls or for a single hull of a multihull.

Catamaran hull length to beam ratio. Typically the LWLBWL ratio will vary from 101 for a good cruising. EU Size factor ZWD 006 LWL ZWD 072. 8 would increase wave making and should be avoided.

WL length of the hull at waterline in ft. It is derived by simply dividing the waterline length of the hull by the waterline beam of the hull. 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.

Larger LB indicates a slimmer hull. 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. I am designing a 30ft coastal cruising catamaran in Jakarta Indonesia and would like to know the ideal beam width for each hull that is suitable for simple and comfortable accommodation.

BeamLength ratio 58 Static stability about 55 knots. Based on Terho Halmes suggestions the lengthbeam ratio of each hull should be between 9 and 12 for a comfortable cruiser. This can be achived on a single hull - no need for a second one.

The wetted lengths at keel LK for test data are calculated from the reported mean wetted length-to-beam ratio λ using the equation L K λ b b π tan β tan τ given by Morabito 2011. Most modern trimarans are a bit higher than that. Typically cruising catamarans will have a beam to length ratio of roughly 50 meaning a 45 long cat will be about 22 wide.

Beam ratio of less than 3 and that thinner is generally better in terms of efficiency and seakeeping. Beam WL beam of the hull at the waterline in feet. Powering While the lengthbeam ratio of catamaran LBRC is between 22 and 32 a catamaran can be certified to A category if SF 40 000 and to B category if SF 15 000.