What is the definition of a "seaplane" according to the rules?

The definition of a "seaplane" according to the COLREGs is "an aircraft designed to maneuver on water." This is correct because seaplanes are specifically built to take off from and land on water, in addition to being able to fly in the air like regular aircraft. The design elements of a seaplane, such as floats or hulls, enable it to operate safely on water surfaces, which distinguishes it from other types of aircraft that are solely intended for flight without consideration for water operation.

In contrast, an option that describes an aircraft designed for flights only does not capture the dual functionality of a seaplane. A definition stating that a vessel operates only above water lacks the critical aspect of water maneuverability that defines a seaplane. Furthermore, a watercraft used for fishing purposes does not pertain to aviation or the specific structure and purpose of a seaplane, which emphasizes its role in both flying and navigating over water. Hence, the correct characterization highlights the unique attributes of seaplanes that align with their operational capabilities.