The two digital photos (core1.jpeg and core2.jpeg) show a plug cut from a 1984 Tayana 37's bulkhead. It is the same plug from seen from two sides - the thickest, and the thinnest. The hole was cut to install ducting for an air- conditioner. The ducting was run along the port side of the interior from the aft-cabin to the v-berth. Holes were cut in each of the bulkheads and pieces of cabinetry under the salon's lower bookshelf and under the counter tops in the head and shower. The piece in the photos was cut using a 6" hole saw from the port-side bulkhead separating the head from the salon. The top of the 6" hole was about 3" below the bottom of the head counter and about 3" in from the inside of the hull itself. The thickest portion was, of course closest to the hull - most of that thickness being tabbing. This thick edge measures about 1 5/8" thick. Most of the glass- layup tabbing is on the forward side of the bulkhead. About 1/2" of the piece is the plywood portion of the bulkhead and, as can be seen, has glass on both sides. The thinest side is 7/8". I was stunned at the thickness of the tabbing and can only imagine how thick it is at the intersection with the hull. Steve Wolfer s/v Island Girl 1984 T37 #420