The waves generated by ships and boats (often referred to as wake wash, wave wake or simply wash) have been known to result in the erosion of riverbanks, damage to maritime structures, or be hazardous to other users of the waterway. The vast majority of research in this field to date has focused on the characteristics of these waves when the vessel is travelling at constant forward speed. Recent work by the authors has identified significant transient effects that occur while a vessel accelerates up to the desired operational speed, where both the height and period of the maximum wave generated are significantly greater than those generated at the corresponding steady-state speed. This notable increase in wave energy can be important, particularly where vessels are required to accelerate on a regular basis when operating in sheltered waterways with limited water depth. Common examples are commuter ferries that make regular passages between passenger terminals and hence pass through the transcritical speed zone to operate at supercritical speeds (in terms of depth Froude number).
In this paper, a study into these transient effects through physical scale-model experimentation is expanded to include different hull forms, including a typical “low wash” catamaran river ferry and a prismatic monohull. Results indicate that the increase in height of the maximum wave can exceed 80% and the period of this wave increase by more than 30% as a result of the acceleration phase compared to the steady-state speed. This poses the question whether these transient effects should form part of the assessment process when considering whether a vessel meets criteria imposed to regulate wash impacts.
The same model scale data is also used to advise the model test community the required distance for a ship model to achieve a steady-state following the acceleration phase during model scale tests in facilities such as towing tanks or basins.