Which part of a boat is known as the upper edge of its sides?

The gunwale is the correct term for the upper edge of a boat's sides. It serves as a structural element that helps to provide strength and rigidity to the hull while also serving as a ledge to walk on or to which other equipment can be attached. Understanding the gunwale is important because it plays a vital role in the overall integrity of the boat's construction and safety features.

The freeboard refers to the distance from the waterline to the upper deck level, which is essential for determining how much of the boat is above the water and its ability to handle waves without taking on water. The port side relates to the left side of the boat when facing forward, which is a directional term used for navigation and communication. The bow refers to the front part of the boat. Each of these terms is vital in boating, but the gunwale specifically identifies the upper edge of the sides, thus making it the accurate answer to the question.