The hydrodynamic performance of marine craft has long been known to be influenced by water depth. When operating in shallow water at subcritical speeds (typical for displacement vessels), they slow down at constant power. On the contrary, when operating in shallow water at supercritical speeds (typical for planing vessels), vessel speeds increase at constant power. Additionally, surface waves generated by the hull vary radically with vessel speed and water depth.
In recent years, mega yachts are being designed for length Froude numbers (FnL) greater than 0.4, with many operating between 0.5 and 1.0, and some have even higher non-dimensional speeds. As these modern mega yachts being delivered have overall lengths up to and often exceeding 100 meters, shallow water effects are being observed by their captains in relatively deep water. Thus, it is the intent of this paper to refresh, for the mega and high speed yacht community, what defines shallow water, the impact on performance and a general discussion on the responsibilities for hull-generated waves and wake occurring due to shallow water. A power prediction procedure applicable in everyday engineering practice is outlined and an underpinned by a numerical example.
