The "stitching" is from the temporary wires used to hold the edges of thin sheets of plywood together until they are "glued." The plywood is sheathed in fiberglass for strength. This is a quick way to make a rugged, lightweight small boat.
I was talking to John Harris at Chesapeake Light Craft last fall. As the conversation wandered around various boats and projects we were working on, it became apparent that we each had some issues that we might be able help each other with.