What aspect of a boat is primarily determined by the height of the freeboard?

The height of the freeboard, which is the distance from the waterline to the upper edge of the boat's side, is a critical factor in a boat's stability. High freeboard typically provides a boat with greater stability because it reduces the likelihood of water entering the vessel during turbulent conditions or heavy seas. This is particularly important in maintaining an upright position and preventing capsizing. A boat with insufficient freeboard may struggle to remain stable, especially in challenging weather conditions, as waves can easily wash over the sides.

While other aspects like capacity, speed, and control may be influenced by the boat's design and freeboard, they do not directly correlate to freeboard height in the same way stability does. For instance, capacity is more related to the internal volume of the hull; speed is determined by hull shape and propulsion; and control is influenced by factors such as rudder design and weight distribution. Thus, among the choices given, stability is the primary aspect determined by the height of the freeboard.