Some Experiments on Anti-rolling Tank for Tankers

Abstract

This paper deals with comparative tests on the performance of an anti-rolling tank of the modified "Flume" type when a large oil-tanker is equipped with it. The purpose of the tests is to get food design data of the tank. The stabilizing action of the tank is derived from remarkable dissipation of energy. The dissipation is caused by the nozzle effect of holes in the longitudinal bulkhead, when the liquid in the tank oscillates through the bulkhead holes according to rolling. When this rype of anti-rolling tank is installed on a tanker, one or two cargo tanks of the tanker are utilized for the purpose. For the tests an anti-rolling tank model with two bulkheads was used and many kinds of bulkheads were prepared for change. The tank model was tested on a "Navipendulum", a rolling simulator and its angle was recorded over an assigned frequency range. As the results of the tests, two cases are successful for roll damping: one is a bulkhead with many small holes, and the other is a bulkhead with a vertical weir. Their frequency response curves show that the roll magnification factor becomes nearly constant and it is around 2.5. Some other cases are thought relatively good. Their response curves show that the magnification factor is relatively low and its peak value is about 3.0, while in the unstabilized condition it shows a much greater value at resonance. It is concluded that the ratio: area of opening in the bulkhead/area of the bulkhead is 0.20〜0.24 for effective damping. The liquid level is also an important parameter and its most effective height is 80 per cent of the tank depth from the viewpoint of roll damping and economy.