The hydrodynamic loads are based on the, within offshore technology, well-known Morrison’s equation. The wave kinematics are not calculated within the HAWC2 code, but provided externally through a defined DLL (Dynamic Link Library) interface, where the present open source DLL includes the water kinematics. The water kinematics includes currents, linear airy waves, irregular airy waves, deterministic irregular waves, stream function wave and can also read pre-generated water kinematic files. Another option is the possibility of coupling the HAWC2 code to a special external system that reads the output generated directly by the wave analysis software, WAMIT. This is especially useful for floating structures where the Morrison’s equation is no longer valid. For large diameter structures, wave diffraction can also be accounted for by the implementation of the McCamy & Fuchs theory.