The paper considers multi-sensor communications between low profile boats, such as unmanned surface vehicles (USVs), in a rough sea environment. We derive the expression of spatial correlation coefficients between two antennas, which is important in designing the configuration of multi-sensor systems. It is assumed that the line-of-sight (LOS) is obstructed by high waves, and the channel distortions by diffraction as well as local scattering are take into account.