Rolling tank
A rolling tank is a tank in the hull of a ship filled with water , which is supposed to dampen fluctuations around the longitudinal axis (the so-called rolling ).
The roll tank was invented by Hermann Frahm , and after initial tests carried out on the City of New York ship in 1889 , it was first permanently installed in the steamer Laconia in 1912 .
The system is basically a water pendulum , which is adjusted to the natural resonance of the ship. It consists of two tanks attached to the long sides of the ship, which are as high as possible and connected with pipes.
If waves hitting the side stimulate the ship to roll, the phase of the ship's oscillation is shifted by 90 ° against that of the impacting waves in the case of resonance. The rolling ship now lets the ballast water flow back and forth between the two tanks. If the natural frequency of this water pendulum (can be influenced by the amount of water and pipe cross-section) matches the natural frequency of the ship, there is a further phase shift of 90 °. Overall, it follows that the phases of the waves hitting the side and the tank water oscillation are shifted by 180 °. The out-of-phase torques cancel each other out, which results in a significant dampening of the rolling movement of the ship about the longitudinal axis.
Since both the oscillation frequency of the ship's lurching and that of the flow around the lurching tank water depend on the amplitude of the ship's oscillation , the interaction is complex.