Effect of optimal thruster location on DP operability of an offshore vessel

In the offshore industry, the thruster layout for dynamic positioning (DP) is not optimal to reach the maximum station-keeping capability. It is possible to optimise the position of the thrusters since early design stage applying a genetic algorithm-based optimisation procedure. The enhancements due to an optimal thruster configuration can be reported in the standard capability plot format as commonly done in the offshore industry. However, besides standard capability plots, additional calculations can be performed by explicitly considering the vessel’s geographic operational areas. By adopting this novel approach, it is possible to associate to vessel’s DP capability an operability index which is specific for the considered sea area and is in analogy of that adopted for ship motion criteria. In this way, the improvements of the optimised thruster configuration can be represented in terms of the increment of DP operability index in a selected sea area, instead of the capability plot area increase for standard conditions. The procedure is here applied to a reference Pipe-lay vessel, where the thruster layout has been optimised. The improvements are reported through both conventional capability plot and newly proposed DP operability index for the North Sea area.