The hydrodynamics of the WIG (Wing-In-Ground) effect craft

Due to its close proximity to the surface of water, Wing-In-Ground (WIG) crafts have much benefits from the increased aerodynamic efficiency which easily translates into fuel saving. This is besides the much higher speed possible of up to O(100) nautical miles per hour for the WIG craft which is at least twice the speed of the fastest water-surface speed boat of less than 50 nautical miles per hour. However, a WIG craft needs to be able to overcome significant hydrodynamic drag to take-off from water. The objective of this work is to investigate the hydrodynamics of a WIG craft through towed-tank test experiment as well as computational fluid dynamics simulation. From the model test, the resistance, sinkage, running trim angle and wetted area are obtained throughout the take-off speed range. Region associated with the highest resistance called hump drag is identified as well as the possibility of secondary hump and slight oscillation are discussed. Despite the complex FSI (Fluid-Structure Interaction) between the hull and water, the good comparison between experiment and simulation shows that the present state-of-the art numerical simulation is a powerful tool for WIG craft designers. An important finding is the critical presence of the stepped hull in overcoming the mentioned humped drag.