Coupling numerical solvers can improve efficiency and accuracy. This thesis aims to couple the spectral Shallow Water Equations (SWE) solver SWEET to the 3D finite volume solver OpenFOAM. The coupling is examined using the versatile preCICE coupling library. Particularly, the challenges of 2D-3D coupling solvers using different simulation schemes and the challenges arising from the SWEET's specific requirements because of its spectral domain are examined. It becomes apparent that the restrictions imposed by this only allow for a limited number of coupling scenarios. A simple one-way atmosphere-ocean coupling scenario is shortly examined. The analysis then focuses on a more complex two-way ocean-ocean coupling scenario. OpenFOAM is used to improve simulation accuracy in a part of the SWEET domain, adding capabilities for obstacles and complex flows, including flows that violate the assumption of hydrostatic vertical pressure gradients. This scenario is useful because, due to its spectral domain, SWEET cannot use adaptive mesh refinement or a domain with geometry due to discretization. The results achieved by the coupled system are evaluated qualitatively and compared to simulations by a single model where possible.