Based on "Principles of Naval Architecture", what happens to the metacentric height (GM) of a ship when weight is added to the top of the ship?

Question

Marina Mariana · Accepted Answer

The metacentric height (GM) is a critical parameter in naval architecture that determines a ship's stability. It is the distance between the center of gravity (G) and the metacenter (M). The metacenter is a point where the buoyant force acts when the ship is given a small angular displacement.


Initial Stability and Metacentric Height:

Initial stability of a ship is determined by the metacentric height. A larger GM indicates better initial stability.
The center of gravity (G) is the point where the weight of the ship acts vertically downwards.
The metacenter (M) is a point where the line of action of buoyancy (upthrust) intersects the centerline of the ship when tilted.



Effect of Adding Weight on Top:

When weight is added to the top of the ship, the center of gravity (G) moves upwards.
This upward movement of G reduces the distance between G and M, thereby decreasing the metacentric height (GM).



Consequences of Reduced GM:

A decrease in GM means that the ship becomes less stable.
In extreme cases, if GM becomes negative, the ship can capsize, as it indicates that the center of gravity is above the metacenter.



In conclusion, adding weight to the top of a ship causes the center of gravity to rise, which decreases the metacentric height (GM), leading to reduced stability. Therefore, the correct answer is B) GM decreases, reducing stability.

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