Justine’s first plank to be “hung” is the one nearest the keel, and planking proceeds working toward the sheerstrake. Because Justine is being built upside-down at this stage, the planking proceeds from top to bottom on the construction molds.
The plank closest to the keel is called the garboard. The frames in this part of the hull are hardly curved at all, so the garboard does not need to be “backed out” on what will be its inside surface. There will be a significant amount of twist in the garboard, but this can be achieved with clamps before the garboard is fastened.
Justine’s planking is northern white cedar, harvested in Maine. My supplier was Bruce Tweedie at Tweedie Lumber in Thorndike, Maine. I purchased about 600 board feet of live-edge planks, rough-sawn to approximately 1″ thick. (One board foot is a volume of lumber that is 1 square foot in area and 1″ thick.)
My planking stock took a variety of shapes, reflecting the shapes of the logs from which they were cut. If the log was from the base of the tree, its end was significantly flared. Only a relatively small fraction of the boards was straight; most were gently curved, which was fine as most of the planks had gently curved shapes. A few of the planks even had reverse curves, giving them an “S” shape. Most of the planks were between 10′ and 13′ in length.
It’s the rare cedar plank that is free of knots. The knots in my planks rarely reached more than 3/4″ in diameter, but many of them were loose and after planing the boards to the required thickness, I used a forstner drill bit to drill them out, drilling about halfway through the board from one side, then filling the resulting blind holes with cedar bungs that I glued in with a mixture of epoxy and microballoons. (The microballoons are tiny hollow latex spheres that serve to thicken the epoxy and also make it much easier to sand.) After one side was bunged, I flipped the board over and drilled and bunged the knots on that side. Once the epoxy had dried, I cut the bungs flush with the plank surface using a sharp chisel and block plane.
The process of determining the shape of a plank before it is cut out is called spiling. I’ll describe spiling in a later post. With the plank’s shape determined, you can go to the pile of planking stock and select a piece that can be used without a lot of waste.
A plank cut to the shape given by the spiling will be a close fit, but still need some trimming to result in a tight seam with the adjacent plank (or with the keel and stem, in the case of the garboard). It’s an iterative process of clamping the plank in place, marking the places where material needs to be removed, unclamping the plank, planing off the excess, and repeating as necessary. Once you’re satisfied with the fit, the plank is close to being ready to fasten.
Justine’s planks are 5/8″ thick, and the frames to which they are fastened are 7/8″ square in cross section, giving a total of 1 1/2″ of material in which to drive a fastener. I chose to use #9 x 1 1/4″ silicon bronze screws for nearly all of the plank fasteners. The screws need a pilot hole for their entire depth; a clearance hole for the screw’s shank in the plank itself, and a counterbore at the surface so that when tightened the head of the screw will lie slightly below the plank surface. (Once the hull is planked and smoothed, the screw heads will be covered over with a filler material. I used “Bondo.”)
Because none of my planking stock was longer than 14′, every one of Justine’s planks needed to be made up of two pieces to cover the distance from stem to stern. So to complete the garboard, a second piece of planking needed to be fitted that would extend back to the transom. The two pieces are butted against each other where they come into contact.
To reinforce the butt joint, it is backed up by a separate piece called a butt block. I made all my butt blocks from pieces of live oak. The butt blocks are 7/8″ thick and they extend about 4″ on either side of the butt joint. They also overlap the adjacent course(s) of planking. Once shaped, the butt block is clamped in place and holes are drilled for fastening it in place.
Before fastening a butt block, the mating surfaces are given a coat of red lead, and a coat of a putty-like material called bedding compound is applied that will help seal the joint yet remain pliable.
With the port and starboard garboards in place, “only” 24 planks remain to be gotten out and hung…