Which TWO of the following cause a small positive GM at the start of a voyage to become dangerous during the passage?
Select the TWO correct answers.
A) Consumption of bunkers in a low tank
B) Consumption of bunkers in a high tank
C) Distribution of weights due to bad stowage
D) Partially filled tanks giving free surface effect
Answer (2)
The two correct answers that can make a small positive GM dangerous during a voyage are the consumption of bunkers in a low tank and the free surface effect from partially filled tanks. Both factors can lead to a decrease in stability, increasing the risks associated with navigating the vessel. Proper management of weight distribution and tank levels is crucial for maintaining ship safety during a voyage.
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When considering ship stability, GM, or metacentric height, is a critical factor that determines how a ship returns to its original position after being tilted. A small positive GM at the start of a voyage means that the ship is somewhat stable but could become dangerously unstable under certain conditions. The two factors that can cause this stability to become dangerous during passage are:
(B) Consumption of bunkers in a high tank:
High tanks refer to tanks that are situated higher up in the ship. When fuel or other materials are consumed from these high tanks, the center of gravity of the ship lowers. This can lead to a higher center of buoyancy overtaking the center of gravity, causing a negative metacentric height, and thus making the ship top-heavy and unstable.
(D) Partially filled tanks giving free surface effect:
The free surface effect occurs when a liquid moves within a partially filled tank, such as water ballast or fuel tank. This movement changes the distribution of weight within the ship, lowering the metacentric height due to the shifting center of gravity. The effect is more pronounced in wide, shallow tanks and can lead to a significant decrease in the stability of the ship if not managed properly.
By understanding these factors, ship operators can take preventative measures, such as managing fuel consumption and ballast levels effectively, to maintain stability throughout a voyage.
