What happens if the trimming moment becomes greater than the max longitudinal righting moment?

• A. The ship will plunge
• B. The ship will capsize immediately
• C. The ship will accelerate without limit
• D. The ship will remain perfectly upright

Answer: (A)

When a vessel’s longitudinal stability is considered, the trimming moment tries to rotate the ship about the center of flotation, while the hull can provide a restoring, or righting, moment up to a maximum value. If the external trimming moment exceeds that maximum longitudinal righting moment, the restoring capability is overwhelmed. There is no equilibrium point to counter the trim, so the vessel will rotate in the direction of the trim and the bow will dig down into the water—effectively a plunge. This describes a loss of longitudinal stability in that direction, which is dangerous and can lead to more severe instability if not corrected.