Permeable Volume – The Forgotten “Galaxy” in Ship Design

Ships are designed on the basis of three basic objectives pertaining to ship performance, functionally and safety, all dictated by external shape, internal layout, deadweight, payload, permeable volume and their distributions. All, with the exception of one are calculated to extremely small tolerances and are subjected to rules and regulations that have been evolving for thousands of years.  The exception, which is of the same magnitude as weight and buoyancy is the permeable volume, namely the internal free space in the ship hull and superstructure (available for flooding). Over the years, some generalised approximations have been adopted for principal ship spaces without differentiating between ship types, leading to gross approximations when calculating, in particular, ship damage stability and survivability. In the latter case, the amount and distribution of residual permeable volume (together with buoyancy and weight), dictate whether a ship may sink or capsize (buoyancy/stability). Yet, all is calculated to extreme accuracy whilst permeable volume and its distribution is calculated with naïve approximation. To demonstrate the impact of such approximations a passenger ship is considered in the paper, offering unique insight on the key influence of permeability on ship safety when considered as an option to reducing and controlling flooding risk.