Vessel Stability and Construction Flashcards

Which of the following describes the 'free surface effect' on a small vessel?

Answer: The reduction in stability caused by the movement of liquid in partially filled tanks or compartments.

The free surface effect occurs when a tank or compartment is only partially full, allowing the liquid to slosh back and forth as the vessel rolls. This movement of liquid shifts the vessel's center of gravity towards the direction of the roll, which reduces the righting moment and can dangerously decrease stability.

A small vessel has a high Metacentric Height (GM). What handling characteristic is it most likely to exhibit?

Answer: A quick, stiff, and potentially violent rolling motion.

A large Metacentric Height (GM) indicates high initial stability. This causes the vessel to have a large righting moment when it heels, resulting in a rapid and forceful return to the upright position. This is known as being 'stiff' and can be uncomfortable and place stress on the vessel and its cargo.

You are loading heavy equipment onto your small vessel. To maximize stability and ensure safety, where is the best place to stow this equipment?

Answer: As low and as close to the vessel's centerline as possible.

Placing heavy weights low in the vessel lowers the overall center of gravity (G). A lower center of gravity increases the Metacentric Height (GM), which enhances the vessel's stability. Stowing the weight near the centerline prevents the vessel from listing to one side.

Which structural component is considered the 'backbone' of a vessel, running along the centerline from bow to stern?

Answer: Keel

The keel is the primary longitudinal structural member of a vessel's hull, running along the bottom centerline. It acts as the foundation or 'backbone' to which the frames and shell plating are attached, providing fundamental strength and rigidity to the entire structure.

A vessel is described as being 'trimmed by the stern'. What does this mean?

Answer: The draft at the stern is greater than the draft at the bow.

Trim is the difference between the forward and aft drafts. A vessel 'trimmed by the stern' is floating deeper at the stern than at the bow. This is a common and often desirable condition for many small vessels, as it can improve handling and propulsion efficiency.

During winter operations, a vessel accumulates a significant amount of ice on its superstructure and rigging. Which of the following is the most dangerous consequence?

Answer: The ice raises the vessel's center of gravity and reduces stability.

While all the options are potential hazards, the most dangerous consequence of ice accumulation is the added weight high above the vessel's original center of gravity. This raises the overall center of gravity, which reduces the Metacentric Height (GM) and critically decreases the vessel's stability, increasing the risk of capsizing.