What is the point at which the weight of the boat acts vertically downwards?

The center of gravity is the correct answer because it represents the point where the total weight of the boat is considered to act vertically downward. This point is crucial in understanding how the boat will behave in the water, as it affects stability and balance. When a boat is subjected to various forces, such as waves or wind, the center of gravity helps determine how the vessel will respond—whether it will remain upright, tilt, or even capsize.

The center of gravity can shift depending on the distribution of weight within the boat, such as the placement of crew, cargo, and fuel. By knowing this point, boat operators can make informed decisions to maintain stability and ensure safe operation on the water.

The other options, while related to boat dynamics, do not specifically refer to the point where the boat's weight acts downward. The waterline indicates the point where the hull meets the water, the hull refers to the physical structure of the boat, and the buoyancy center relates to the point where buoyant force acts, which can differ from the center of gravity. Understanding the importance of the center of gravity is key to effective boat handling and safety at sea.