Investigation on the Interaction between Ship Propulsion Control System and Manoeuvrability by Time Domain Simulation

Use of electronic control onboard to handle complex and powerful propulsion systems has constantly increased; this, in turn, may influence ship behaviour during manoeuvres. As it is well known during manoeuvre of a twin-propeller vessel, like turning circle or zig-zag manoeuvres, significant unbalances on the shaft lines, in terms of torque and thrust loads, are experienced. As regards the propulsion and the control system design point of view, this aspect has to be taken into account together with the general increase of the shaft torque with the respect to the steady state value. To prevent possible problems, the control system must be properly set, through dedicated control functions, to maintain the shaft torque or the engine torque below the allowed levels, to reach and maintain the wanted rotational shaft lines regime, etc. In present paper, a comprehensive approach to simulate the interaction between the ship propulsion system and manoeuvrability, during transients and off design conditions, is presented. The behaviour of the ship is simulated by means of a numerical model, developed by the authors, which includes the ship dynamics (3 D.O.F. model), the propulsion plant dynamics (i.e. prime movers, shaft lines, propellers, etc.) and the control system dynamics. This model has been calibrated by means of an extensive free running model campaign, simulating the manoeuvres in model scale, carried out with simplified control schemes. At the end of this paper some simulation results are shown in order to better understand the effects of the propulsion control settings on the expected dynamic behaviour of the ship at full scale.