Using a mature Reynolds Averaged Navier-Stokes (RANS)-solver for ship stern flows as a starting point, the authors consider some possibilities to enhance efficiency and robustness without sacrificing accuracy. Among them are alternative domain decompositions and vectorizable preconditioning techniques. It is shown that a good balance between flexibility, robustness and efficiency can be obtained and that it is justified to neglect diffusion in the main stream direction and some of the convective terms.