Dynamic Positioning: Early Design, Capability and Offsets—A Novel Approach

Abstract

Many vessels use a Dynamic Positioning (DP) system that automatically controls vessel position and heading with its own propulsion system. The limiting environment in which a vessel can maintain heading and position under DP operation is typically shown in a capability plot. Capability is usually evaluated assuming constant environmental forces — the static DP approach. In this paper we discuss the methodology of how such a capability assessment can be made early in the vessel design stage. The insights obtained in the heading and position variability over time, and the effects of the environmental forces varying with time can be assessed through model tests and time domain simulations: the dynamic DP approach. This implies that the DP system characteristics are modeled. In a numerical approach, the time variable wind load and low-frequency drift forces are included in the assessment. This paper presents a novel approach on how static DP capability calculations can be corrected to account for the time variable wind and wave drift forces. This leads to a DP capability plot that provides a more realistic insight in the actual DP capability of the vessel in the dynamic environment.