What is referred to as the upper edge of the vessel's side?

The upper edge of a vessel's side is specifically referred to as the gunwale. This term originates from the Old Norse word "gunnail," which means the "top of the side." The gunwale serves as a structural component that provides support for the vessel's sides and helps to prevent waves from entering the boat. It often provides a relevant area for securing lines, mounting equipment, or ensuring safety for those onboard.

The other terms refer to different parts of the vessel: the port side refers to the left side of the boat when facing forward; the transom is the flat part at the back of the boat; and the deck is the horizontal surface that covers the interior space of the boat. Understanding the terminology and structure of a vessel is crucial for safe navigation and operation.