Analysis of thruster effectivity for dynamic positioning and low speed manoeuvring

Dynamic positioning, tracking and low-speed manoeuvring have for a long time defied attempts to properly analyse and predict the performance. This is undoubtedly due to the complexity ofthis dynamic problem where not only hydrodynamic aspects are important but where also control aspects form an integral part of the system. Traditionally the field of DP or low-speed manoeuvring was analysed by splitting the problem into smaller parts more amenable to analysis. These parts are for example environmental forces (waves, wind and current), control systems and propulsive forces. Each aspect was considered separately and no full coverage of the problem was undertaken. With the development of time-domain simulation programs more integral analyses were undertaken which, despite their complexity, yielded valuable results pertaining to the design and operability assessment. Despite this major step forward, many white areas remain in the description of the various components relevant for this topic. One of these components is the force that can be generated by propellers, rudders and thrusters during the low-speed manoeuvers inherent to DP, tracking and harbour manoeuvers. The large number of parameters involved in this particular problem do not allow an experimental and systematic coverage ofthe various phenomena. Instead recourse must be taken to a combination of experiments and calculations which together eventually will yield a prediction tool that can be used to further improve the analysis of low-speed manoeuvers. With CFD codes finding their way in practical applications, such a combined analysis is gradually becoming feasible. Experiments are then used to validate and complement computations. The present work is the first such approach to the particular problem of thruster effectivity during DP, tracking and low-speed manoeuvers.