Deep water entry of high speed ferry bows

High speed multi-hull ferries can experience strong vertical motions near the bow when encountering heavy seas and risk bow damage due to deep entry into encountered waves. The risk of water passing over the top of the bow has been virtually eliminated in the INCAT Tasmania Wave Piercer design which incorporates a centrebow with a keel on or above the waterline. However, confinement of displaced water in the connecting archways to port and starboard of the centre bow leads to large hydrodynamic loads on the bow structure. The time dependant water entry problem for a high speed wave piercer vessel is extremely complicated owing to the relatively complicated form of the bow areas of the hulls. Determination of the hydrodynamic loads which can occur has therefore been based primarily on experimental testing at full scale and at model scale, but CFD methods are also being investigated. As the bow enters an encountered wave, water is at first displaced by the centre bow and ejected over the top of the forward ends of the demi-huills. However as the water entry event develops the rising water surface can ultimately fill the arch cross section and at that stage the hydrodynamic loads can become extremely large. Maximum loads in excess of the total displacement of the vessel (that is in excess of 2500 tonnes at full scale typically) have been observed and have durations of about 0.4 seconds at full scale.