Permeable volume – the forgotten "galaxy" in ship design

Ships are designed based on 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, except for one, are calculated to extremely small tolerances and are subjected to rules and regulations that have been evolving for thousands of years. The exception is "permeable volume", (the internal free space in the ship hull and superstructure available for flooding), which is of the same magnitude as weight and buoyancy. Over the years, some generalised approximations have been adopted for principal ship spaces without differentiating between ship types, leading to gross approximations when calculating ship damage stability. In the latter case, the amount and distribution of residual permeable volume (together with buoyancy and weight), dictate whether a ship may sink because of inadequate buoyancy or capsize due to loss of stability. Yet, whilst all pertinent parameters are calculated to extreme accuracy, permeable volume and its distribution is calculated with naïve approximation. To demonstrate the impact of such approximations several passenger ships are considered in the paper, covering the whole range of ships in operation, and a sensitivity analysis is undertaking addressing the main ship spaces and their contribution to permeable volume, offering unique insight on the key influence of permeability on ship damage stability. Building on this, the impact of permeability as a key design option to affect life-cycle stability management is elaborated and demonstrated, leading to conclusions and recommendations.