Admin Table of Contents
What is the effect in stability of the tank is slack?
Liquid in partially filled tank always decreases the initial metacentric height GM, righting lever GZ, and angle of vanishing stability. A partially filled tank is know as a “slack tank”. The reduction of stability caused by the liquids in slack tanks is known as free-surface effect.
What is slack tank?
marine. Any tank that is not totally empty or pressed full.
Why angle of loll is dangerous?
Although a vessel at angle of loll does display features of stable equilibrium, this is a dangerous situation and rapid remedial action is required to prevent the vessel from capsizing. It is often caused by the influence of a large free surface or the loss of stability due to damaged compartments.
Is the turning effect that tends to capsize the ship?
As the ship is inclined, negative Righting Arms (called upsetting arms) are created which tend to capsize the ship. When a ship is inclined through all angles of heel, and the righting arm for each angle is measured, the statical stability curve is produced.
What is the effect of the stability if the GM is large?
If GM is large, the ship has large righting arms and will have stiff, fast rolls….CRITICAL STABILITY.
| Critical Thumbrule | Actions to be Taken |
|---|---|
| Negative GM | FLB, Eliminate FSE/FCE, Shift Weight Down, Add Weight Low, Remove Weight High (Symmetrically) |
What is the situation that affect vessel stability?
Stability is determined by the force of buoyancy provided by the underwater parts of a vessel, coupled with the combined weight of its hull, equipment, fuel, stores and load. These forces can also be adversely affected by the prevailing weather conditions and sea-state.
What is free communication effect?
Free Communication Effect occurs when the ship’s hull is ruptured, allowing sea water to flow in and out as the ship rolls. This continuous weight addition and removal causes a horizontal shift in the center of gravity, which then equates to another virtual rise in the center gravity.
What is negative stability of a ship?
If the centre of gravity (G) of a vessel is above the metacentre (M) the vessel is said to have a negative GM or a negative initial stability. A vessel in this state has a loll, i.e. it floats at an angle from the upright to one side or the other and there is a danger that it may capsize.
What is the purpose of angle of loll?
The angle of Loll is that angle of heel at which a ship with negative GM will come to rest. It is an extremely dangerous situation and in extreme cases, a vessel may even capsize. A vessel with Negative Initial GM will tend to capsize.
What is free surface effect in slack tanks?
The reduction of stability caused by the liquids in slack tanks is known as free-surface effect. This adverse effect on the stability is referred to as a “loss in GM” or as a “virtual rise in vertical centre of gravity KG” and is calculated as follows: Loss in GM due to free surface effects (in metres) = Free surface moment (tones metres)
What is a slack tank and a full tank?
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”. Vessels are designed so that weight doesn’t easily shift with the motion of the vessel. Things are secured, or can be secured, in some fashion.
Do slack tanks overstate your obq?
· If you have a slack tank (s) before discharging but empty after then your discharge figures will be overstated. · If you have a slack tank before and after discharging it is a lottery and you could have even larger variances. · Follow our guidelines and you will reduce your risk substantially. Slack tanks prior to receiving overstates your OBQ.
How to tell if a cot tank is slack?
IT SHOWS SOME VERY GOOD ANIMATION SHOWING HOW HIGH THE SLACK TANKS ‘SLOSH’ AROUND. WHEN THE CARGO TANK MEASUREMENT POINTS ARE EITHER AFT OR STARBOARD THE SITUATION IS MADE EVEN WORSE. When a vessels COT is slack and the vessel is moving the COT structure can also move.