Wave Reduction by S-Catamaran at Supercritical Speeds

The S-catamaran is a catamaran with twin hulls that are slightly curved in an S-form and arranged at a mean yaw angle but mirror symmetric to their common longitudinal centerplane. Theoretical studies (Chen & Sharma 1997, Chen 1997) show that by proper choice of the sectional area curve, separation, curvature, and yaw the waves generated by the component hulls cancel each other at a supercritical design speed, and consequently the wave wake and wave resistance can be substantially reduced. Theoretically, an almost complete elimination of the waves would be conceivable for an S-catamaran. To verify this theory, a model experiment with an S-catamaran was recently carried out in the VBD. The S-catamaran (Chen & Sharma 1997) was designed to have the same length and displacement as the VBD model series M601, which was developed and tested much earlier in the VBD by Heuser (1973). Despite certain deviations from the ideal form for practical reasons, the wave resistance of the new curved-yawed-hull catamaran with and without skeg was numerically found to be less than that of an equivalent straight-unyawed-hull catamaran by 50% and 30%, respectively. Now, the new design, albeit without skeg, has been validated by a model experiment. In comparison with a reference catamaran of the series M601, up to 28% wave-resistance reduction was achieved in the experiment, although not in the originally designed configuration but at a reduced yaw angle found by trial and error.

An Optimization Study for the Bow Form of High-Speed Displacement Catamarans

ABSTRACT Interest in high-speed marine transportation has acquired a wide variety of hydrodynamic research activities on catamarans, including shape optimization for minimum total resistance. This study attempts to utilize the mathematical programming in optimizing the bow form of twin hulls for minimum total resistance as well as in analyzing the optimization by physical model tests. The total resistance is assumed to be composed of wave-making and frictional components, which are formulated using Michell's thin-ship theory and ITTC-1957 friction line, respectively. The optimized hull form is analyzed by means of a computational flow solver before going through the experimental analysis. The study demonstrates the capabilities of the optimization procedure, presented for catamarans, in reducing the total resistance, as well as its limitations to be used as a design tool in a relatively high-speed zone.

A Strip Method for Lateral Drift Force of a Semisubmersible

This paper presents the results of an application of a strip technique for the prediction of the lateral drift forces on a semisubmersible platform floating in oblique regular waves. The method employs Maruo’s formula and source distribution technique, without taking account of the hydrodynamic interaction between the twin hulls and columns of the semisubmersible. Overall the strip technique shows a more favorable correlation with the experimental data than the three-dimensional theory. It is, however, premature to conclude that the technique has been fully validated.