Assessment of Station Keeping Capability for Dynamically Positioned Offshore Supply Vessel

Abstract Dynamic positioning capability (DPCap) assessment is essential during the preliminary investigation of the positioning ability of a newly designed dynamic positioning system (DPS). Operational safety is always the first consideration in the design and operation of a new DPS. To be able to plan a safe and efficient operation, it is important to know the maximum environmental conditions that the DP vessel can withstand. The main objective of this article is to present a developed tool capable of conducting the DPCap analysis for offshore supply vessels based on the DNVGL methodology. The article describes the background studies, methodology, and mechanism associated with the formulation and development of the tool. The optimization of the design variables for the station-keeping criteria targets the highest capability at the lowest possible energy expenditure. Finally, the results are presented in the form of standard capability polar plots to show the application of the computational assessment procedure. The accuracy and reliability of the DPCap tool are validated by comparing with the results of the commercial one for the same case study ship at multiple simulation cases. Introduction Many offshore operations require the vessel to be kept in a position to face environmental loads from wind, waves and current. This can be achieved using Dynamic Positioning System (DPS) by using thrusters (Sørensen 2011). Station keeping ability is used in different types of vessels with varying operational requirements. Cruise vessels and mega yachts use it in the form of virtual anchoring to avoid the environmental impact of anchoring in the sensitive estuaries they often ply. The importance of DPS is growing because of the increase in the number of offshore construction sites requiring DPS for their operations (Mehrzadi et al. 2020). Over the last four decades, dynamic positioning (DP) in deep water has been used in the marine sector, oil and gas industries, and military services in many tasks such as drilling, oil and gas floating production platform, cable, and pipe laying, docking and towing, firefighting, supply, search and rescue, surveying, and mobile offshore bases (MOB). Each of these operations benefits from a DP system’s ability to include precise position-keeping, freedom from the restrictions of mooring spread systems, the ability to move quickly from one site to another, and track-keeping capabilities (Elkafas et al. 2021; Mahfouz 2007).