Question 61

The Correct Answer is A. **A) GM (Metacentric Height)** is the correct indicator because it represents the vertical distance between the center of gravity (G) and the transverse metacenter (M). For a ship to possess **initial stability** (stability at small angles of heel), the metacenter (M) must be above the center of gravity (G). A positive GM value indicates a stable condition, as it confirms that the righting arm will be positive at small angles of heel, ensuring the ship returns to an upright position. Therefore, GM is the standard quantitative measure of initial stability. **B) GZ (Righting Arm or Statical Stability Lever)** is incorrect because GZ is the measure of the ship's stability at a specific **angle of heel ($\theta$)**. While stability depends on GZ being positive, GM is the specific indicator of *initial* stability (at $\theta \approx 0$). **C) KM (Height of the Metacenter above the Keel)** is incorrect because KM defines the location of the metacenter (M) relative to the keel (K). While KM is a component used in calculating GM (GM = KM - KG), it is a measure of the ship's geometry (form stability) and does not, by itself, indicate stability unless the location of G (KG) is also known. **D) KG (Height of the Center of Gravity above the Keel)** is incorrect because KG defines the location of the ship's center of gravity (G). High KG values reduce stability, and low KG values increase it, but KG alone is not the indicator; the relationship between KG and KM (which yields GM) determines stability.