Quantitative evaluation of the mass-flow effect of seawater with inhomogeneous density upon the vertical cylinders (supports of submersible and semi submersible drilling platforms) has been performed considering water flows, induced superficial and internal waves. Calculated results are compared with experimental data obtained previously in the basin with stratiphied water. The modal structure and amplitude-phase parameters of internal waves generated by a vertical cylinder crossing the free surface and the surface pycnocline are studied as functions of the cylinder velocity and submergence depth relative to a density jump.