Objectives  The ship turning motion can reflect the steerability of the ship during navigation and is closely related to the ship navigation safety.

  Methods  In this paper, the direct numerical simulation of the free turning motion of the standard ship model ONRT in waves is carried out by using CFD solver naoe-FOAM-SJTU based on overset grid technology. The dynamic overset grid technology is used to solve the complex motions of the ship, propeller and rudder systems, and calculate the medium propeller speed corresponding to the self-propulsion point of model in still water. The free turning motion of 35° is realized here.

  Results  Through the global solution of the fully viscous flow field, 6 DoF motions of the ship in the waves and hydrodynamic load changes of the propeller and rudder are given. The parameters of the ship turning motion in waves are presented and compared with the available test results. Wave effects on the free turning motion are discussed through detailed flow visualizations. The ship's motion trajectory and the parameters of the turning motion obtained by numerical prediction are in good agreement with the test values, which fully proves the applicability and reliability of naoe-FOAM-SJTU solver in the numerical prediction of the ship's free turning motion under the hull-propeller-rudder interaction of the ship.

  Conclusions  Through numerical simulation of the turning motion, it provides an effectively preliminary assessment for the steerability of the ship.