Which two forces primarily determine a vessel's stability?

Which two forces primarily determine a vessel's stability?

• A. Wind and Current
• B. Thrust and Drag
• C. Gravity and Buoyancy
• D. Momentum and Inertia

Answer: (C)

Stability hinges on how weight and buoyant force interact. Gravity pulls downward through the vessel’s center of gravity, while buoyancy pushes upward through the center of buoyancy. When the hull heels, the buoyant force shifts position, creating a turning moment. If the metacenter sits above the center of gravity, this moment is restoring and helps the vessel return upright; if not, the vessel becomes unstable. So the two forces that primarily determine stability are gravity and buoyancy. Other forces like wind, current, thrust, or drag affect motion and loads, but the static stability basics come from how weight and buoyant force line up.

Stability hinges on how weight and buoyant force interact. Gravity pulls downward through the vessel’s center of gravity, while buoyancy pushes upward through the center of buoyancy. When the hull heels, the buoyant force shifts position, creating a turning moment. If the metacenter sits above the center of gravity, this moment is restoring and helps the vessel return upright; if not, the vessel becomes unstable. So the two forces that primarily determine stability are gravity and buoyancy. Other forces like wind, current, thrust, or drag affect motion and loads, but the static stability basics come from how weight and buoyant force line up.