Flo-Flo (Float On/Float Off) ships are characterised by their large number of ballast water tanks. These make it possible to lower the ship until the main deck is below the waterline. This allows large floating loads to be loaded. The cargo is lifted out of the water and balanced by pumping out or blowing out the ballast water tanks. To avoid damage to the ballast water tanks from overpressure or underpressure, the internal tank pressures and levels require continuous monitoring.