Author(s)

R. S. Mercier & F. A. Huijs

Abstract

There is very little information available in the public domain on steady current forces on tanker-based Floating Production, Storage and Offloading systems (FPSOs). The general lack of available data and unresolved issues related to scale effects in model tests bring into question whether the level of uncertainty in modelling of current forces on FPSOs is sufficiently well understood, which has implications for the design of FPSO station-keeping systems. This paper presents the results of a test program to measure current forces on a tanker-based FPSO at various current speeds and relative current headings. While the results are in general agreement with the design curves published by OCIMF, there are some important differences associated with the effect of bilge keels and the effect of lift forces generated by vortex shedding from the bow and stern. Keywords: current forces, tankers, FPSOs, scale model tests, bilge keels. 1 Introduction Steady forces exerted by ocean currents on deep draft, column-based structures such as tension leg platforms or spars are relatively straight forward to estimate using textbook information on bluff body drag. In the case of tanker-based Floating Production, Storage and Offloading Systems (FPSOs), there is very little public domain information on drag and lift forces in steady currents that can be used for routine design calculations. Remery and Van Oortmerssen [1] presented a method to predict current forces on moored tankers based on several model tests conducted at the Netherlands Ship Model Basin (currently MARIN). Since the authors felt the small longitudinal forces were not measured with sufficient accuracy, they proposed that the ITTC-1957 frictional resistance formula be used to predict the longitudinal force. For the transverse force and yaw moment coefficients they

Keywords

current forces, tankers, FPSOs, scale model tests, bilge keels.