A Simplified Method to Predict the Added Resistance of a SWATH Ship in Waves

A simplified method called phase transfer is used to calculate the added resistance of a SWATH ship advancing in regular waves. Using the method, the total added resistance of the twin-hull body can be obtained by calculating the corresponding hydrodynamic forces of a single body only. There is no need to calculate the force on each body twice, and the hydrodynamic interactions are not included. The strip theory is still used and the nonlinear force prediction is based on the theory for a monohull ship advancing in waves. Two additional assumptions are also made: (1) the hull body is a "weak scatterer" and (2) the second-order potential is small and can be neglected. Practically, the present method is suitable for predicting the corresponding hydrodynamic properties of a SWATH ship with high speed because the hydrodynamic interactions are not significant. The results obtained in the paper mostly agree with the experimental data and show that the present idea is reasonable. It is also found that the inclusion of the interaction between two hulls may lead to some unreasonable negative added resistance in bow waves. Therefore, the method developed here can be considered as a simpler tool to analyze the added resistance for SWATH ships advancing in waves, especially for higher speed.