ABSTRACT
In recent years, the rapid growth of the high-speed catamaran industry has highlighted problems in the way in which full scale vessel resistance is calculated from model tests. Using the traditional approach the total resistance can be broken down into Froude and Reynolds number dependent components. These are then scaled according to their respective scaling laws.
The common practical method of separating the resistance components is by use of a form factor to estimate the total viscous component. In the case of the catamaran, the form factor will include the interaction effects between the demihulls: changes in the boundary layer due to the modified pressure field around the demihulls; and the influence on frictional resistance of the velocity augmentation between the demihulls.
Of major interest, in the field of high-speed catamarans, is the appropriate magnitude of the form factor and its dependence on hull and operational parameters such as length/displacement ratio, breadth/draught ratio, separation/length ratio, and Froude number. Historically, the choice of form factor for slender catamaran forms has often been close to unity. However, recent research, from a number of independent researchers working in this field, has indicated that this may not be the case and that form factors greater than unity may be appropriate for these vessels.
This paper presents the results of work carried out at the University of Southampton (UK) and the Australian Maritime Engineering Co-operative Research Centre which has sought to gain a better understanding of the resistance components of high-speed catamarans and the appropriate form factors to be used for resistance scaling.
Keywords: ship resistance, Froude number, Reynolds number, high-speed catamarans, form factor, interaction effects.