What is a slack tank on a ship?

The free surface effect is a mechanism which can cause a watercraft to become unstable and capsize. When referring to the free surface effect, the condition of a tank that is not full is described as a “slack tank”, while a full tank is “pressed up”.

What causes a free surface effect?

Free surface effects are not only caused by partially-filled tanks. They can, for example, also be caused by accumulated water on deck. To enable the water to run off quickly, a vessel should have adequate freeing ports.

How do you reduce FSE?

Free Surface Effect can be decreased , to a certain magnitude, by inducing pocketing. Pocketing happens when the surface of the liquid comes in contact with the top or bottom of the tank thereby reducing the breadth of the free surface area.

What is the effect of slack tank on the movement of the ship when it is rolling?

When any tank or a compartment is partially filled, the motion of the liquid (due to the ship’s rolling and pitching motions) would reduce the stability of the ship.

What is pocketing in free surface effect?

Free Surface Effect can be reduced, to some extent, by creating pocketing. Pocketing occurs when the surface of the liquid contacts the top or bottom of the tank, reducing the breadth (B) of the free surface area. The Free Surface correction will therefore indicate less overall stability than actually exists.

What is the meaning of slack tank?

marine. Any tank that is not totally empty or pressed full.

What would happen if the metacentric height is negative?

If the metacentric height of a ship is small, the righting arms that develop will be small. Even with negative metacentric height, ships with certain forms can still find a position of stable equilibrium at an angle of heel called angle of loll. The angle of loll should be corrected only by lowering the gravity center.

What is the free surface effect of a slack tanks?

When a tank is partially filled, the liquid’s centre of gravity position will change as the ship is inclined. Liquid in partially filled tank always decreases the initial metacentric height GM, righting lever GZ, and angle of vanishing stability.

What will happen to your ship if you have free surface effect?

The free-surface effect can endanger the ship or even lead to a negative metacentric height. When ballasting the vessel, only one transverse pair or a single centerline ballast tank should be filled up.

When the ship moves and incline due to slack tank What will happen to the center of gravity?

Is the difference between FWD Draught and aft Draught?

The draft forward (bow) is measured in the perpendicular of the bow. The trim of a ship is the difference between the forward and aft draft. When the aft draft is greater the vessel is deemed to have a positive trim, and it has a negative trim when the forward draft is the greater.

What does the phrase slack tank of the ship mean?

: ‘The slack tanks of the ship’. My doubt is: “slack tank”. Slack in this case means not completely full. When a ship is in motion, the liquid in a slack tank sloshes around which can cause stability problems as the weight of the liquid is constantly shifting.

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