The correct answer is D) stringer plate. The stringer plate, labeled as "A" in the illustration, is a continuous longitudinal structural member that runs along the side of the hull, just below the sheer strake. The stringer plate provides additional strength and support to the hull structure, helping to distribute the stresses and loads. The other options are incorrect because: A) deck longitudinal refers to a structural member running lengthwise on the deck, not the side of the hull. B) the sheer strake is the topmost strake of the hull, above the stringer plate. C) the deck strake refers to the planking or plating that makes up the deck, not the side of the hull.