Ship-ship hydrodynamic interactions are studied using URANS computations for Hope and Bobo in replenishment condition in calm water and waves and in overtaking maneuver in waves. The experiments were performed by MARIN and include a wide range of speed, heading, spacing, and configuration. The simulation matrix is selected to validate URANS capability and study the complex physics involved. Most of the simulations are completed and some are to be run as future work. The physics are explained using the extensive global and local flow information produced by current simulation. The calm water results are validated with EFD, average error being 21%D, and the interaction effects are investigated through comparison with single-ship computations. For replenishment in waves, the MARIN data was previously used to evaluate different simulation tools based on a range of methods from dynamic simulators to time domain panel method solvers. The average error values are 10%DR for current URANS, 15%DR for Rankine panel method, 32%DR for Green's function method, and 38%DR for dynamic simulators. The interaction effects on 0th and 1st harmonics are quantified and different effects compared. Sheltering is found to have most significant effect for oblique waves, 105% for the current conditions. The effects of spacing are found more significant for head waves than for 120 deg waves where sheltering effects are present, being 43% and 23%, respectively. An overtaking simulation in regular head waves is carried out where Hope (larger ship) overtakes Bobo with speed ratio of 1.6. The interaction effects are present from the beginning of the simulation when Hope is in the wake of Bobo, and are most significant during overtaking. The important effects include decreased motions and increased Y, K, and N as the ships pass by each other, being more significant for Bobo (the smaller vessel).
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