A numerical analysis on the drainage capacity of a ropax vessel in the garage deck, in still water and in waves

The ropax vessels are designed to provide the transfer of vehicles, cargo, and passengers and to ensure maximum comfort and safety. The absence of a transversal subdivision for all vessel length poses serious threats to ship safety in case of flooding of the garage deck. When the floodwater is not properly and efficiently drained overboard it can have detrimental consequences both on ship stability, due to large free surface effects and, on loads on deck structures due to the pressure of the accumulated water. In this paper, we propose and apply a fast numerical method for the study of the drainage capacity in the garage deck of a ropax vessel assuming a passive drainage system i.e. comprising only scuppers, whereas the investigated flooding scenario depends on fire fighting operations. The effectiveness of the drainage system is simulated accounting for ship dynamics in calm water and in waves, by adopting a hybrid non-linear numerical model. Flooded water is modelled by lumped mass method; the couplings between ship and floodwater dynamics is achieved by the apparent gravity technique. Two scupper configurations are considered, by modifying scupper dimensions and positions on board. Several numerical simulations are carried out assuming also partially inefficient scuppers. The analysis of the obtained results can provide a general support for the design of passive drainage systems. Based on the outcomes of the case study, this research discloses an improvement in the drainage system when more scuppers are allocated at the stern zone.