It is known that a submarine during her motion in rough seas near sea surface, or in surfacing as well, as in heaving in a surface position may become unstable in rolling/pitching modes. This event may occur due several reasons:

-   the known “suction” force acting by waves ;

-  seawater into the upper permeable section of the outer hull cannot flow out immediately once the submarine is surfacing;

-   the submarine center of gravity is higher than in design surface position due to same water into the upper permeable section.

The submarine heave (up and down) oscillations in a surfaced position may lead to a roll instability, also known as parametric resonance

These factors influence on a submarine behavior being under/on sea surface and can lead to periodic emergence of the submarine instability and great rolling amplitudes that can get very high without inputting much energy.

Computer time domain simulation is done for the submarine moving near or crossing a sea surface surfacing for examination of the mentioned propositions. In the computer time domain simulation the following phenomena has been taken into account:

-  changes in water plane area during surfacing/submerging, when a metacentric height value reduces consequently

-  influence of residual water in permeable parts of a submarine hull and ballast tanks

-   second order wave forces and moments acting in vertical plane (suction forces)

The requirements (based on the results of the examination of the computer simulation) on a submarine hull (upper part) design and upon the best submarine position in surfacing or floating in a surfaced position (i.e., on the optimal submarine ballasting) are developed.