What is sloshing?

In this article, I propose to understand the concept of sloshing.

Within a range of tank filling levels, the natural pitching and rolling movement of the ship at sea, and the liquid free-surface effect, can cause the liquid to move within the tank. It is possible for considerable liquid movement to take place, creating high impact pressure on the tank surface. This effect is called “sloshing” and can cause structural damage.

Sloshing is a problem which effects membrane constructed tanks. Independent containment systems such as the spherical Moss design and the IHI prismatic designs are not subject to the same sloshing impacts. Partial loading at any tank filling level is inherent in the design of Moss design tanks, giving them distinct advantages over membrane containment systems, when handling spot trades and offshore loading/unloading.

Sloshing impact occurs when there is a sudden change in the wetted surface due to liquid motion in the tank. In a partially filled compartment, a wider area on the tank wall is vulnerable to the sloshing impact of the cargo.

Therefore, if the structure of the tank may be influenced by “sloshing”, there must be “Tank filling limits” for each tank on board. The lower and upper limits of the admitted tank filling. If the level of the liquid in tanks is lower than “Tank filling limits”, then structural damages may appear in case of bad weather. Cargo Officer must know those limits!

Normally this limit is as follows: Higher than a level corresponding to normally 70% of the height of the tank, but filling <98 %.

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