Suction of ships (vessels) is a phenomenon of mutual attraction of ships when they move at short distances from each other (for example, in narrow spaces), which takes place in the practice of both sea and river navigation. It can manifest itself both when ships pass each other on opposite courses, and when one overtakes another on a parallel course. The reason for the occurrence of suction is said to be the pressure difference and the appearance of hydrodynamic forces between two closely located hulls of moving watercraft.