Abstract: A tank (10) of a ship (1) is provided with an inflow port (6) and an outflow port (7) opening through a bottom of the ship (13). The inflow and outflow ports are spaced apart from each other in a headway direction of the hull. The ports are equipped with closure means (9), which closes the ports so as to ensure hull buoyancy by means of air in the tank. The ports allow seawater outside the ship to flow into the tank through the inflow port and the seawater in the tank to flow out of the ship through the outflow port, with use of headway motion of the ship. A partition (2) provides a weir extending in a widthwise direction of the hull in the tank, and divides a region in the tank into an inflow area (3) and an outflow area (4). The tank, partition, inflow port, outflow port and closure means constitute a ship buoyancy control system.

Abstract: A tank (10) of a ship (1) is provided with an inflow port (6) and an outflow port (7) opening through a bottom of the ship (13). The inflow and outflow ports are spaced apart from each other in a headway direction of the hull. The ports are equipped with closure means (9), which closes the ports so as to ensure hull buoyancy by means of air in the tank. The ports allow seawater outside the ship to flow into the tank through the inflow port and the seawater in the tank to flow out of the ship through the outflow port, with use of headway motion of the ship. A partition (2) provides a weir extending in a widthwise direction of the hull in the tank, and divides a region in the tank into an inflow area (3) and an outflow area (4). The tank, partition, inflow port, outflow port and closure means constitute a ship buoyancy control system.