A practical approach to determine the structural design loads of turret moored FPSO (Floating Production Storage and Offloading) tankers is suggested in this paper. The linearized restoring forces acting on the ship hull by the mooring system are calculated according to the catenary theory. The effect of the restoring forces is included in the equations of motions of the ship in the form of linear stiffness coefficients. The hydrodynamic coefficients are calculated by the three-dimensional potential flow theory. The equations of motions are solved in frequency domain, and the motions and wave loads responses can be obtained. Then the short-term and long-term analyses are carried out for the wave loads of this kind of ship. With a 250m turret moored FPSO tanker as an example, according to the given environmental sea states data, headings, exceeding probability for the FPSO tanker, the structural design loads are calculated and compared with those obtained from rules for traditional tankers with the same dimensions. By the present approach, it is possible to perform a practical and efficient calculation of structural design loads of actual turret moored FPSO tankers.

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