Aft Sections ( 5 - 8 ) - The aft cross sections are flat on top, with the gunwales and deckridge at the same height. To insure accuracy, first place small sections of aluminum tubes in the 3/4" gunwale cutouts. Next, place a ruler on top of the tubes and draw a line between them. This line will determine the top of the deckridge tube for each cross section. Drill the deckridge cutout hole based on this line.