Dynamics of larger merchant ships during harbour towing operations by using continuous time simulation and CFD techniques

Towing a large ship in harbour during severe weather conditions may be fraught with potential hazards, so that accidents during towing operations are all too common. With regard to the minimization of collision risks, simulation can be used as a powerful tool to plan safer and safer emergency towing arrangements and procedures. This paper deals with the numerical model developed by the authors to represent the berthing and towing/escorting operations referred to a container ship towed by two tugboats. The virtual scenario, assumed for the simulation, regards a towing operation in emergency situation, due to the high speed of the wind and the accidental loss of the main propulsion of the ship. The wind action on the ship has been modelled by CFD method, used in order to compute forces in correspondence to the actual ship shape and loading condition and to represent the influence of harbour breakwaters upon them. The simulation results, achieved over time, can be successfully employed to investigate particular towing issues, as the proper use of the number and power of tugboats. A good towage service provides towing and general assistance (pulling, pushing, escorting) to facilitate the berthing and mooring operations of large ships.