Justine has 12 cedar planks on each side of the hull. Planks are hung sequentially from the garboard to the sheerstrake. Justine’s sheerstrake is effectively a large mahogany molding and making it is an involved process that I’ll treat in a separate post. The previous post described how I spiled the planks and illustrated fitting and fastening the garboards.
In theory, hulls are symmetrical about the boat’s centerline. Justine was my first attempt at building a carvel planked boat, and I was pleasantly surprised to find only relatively minor departures from symmetry between port and starboard halves of the hull.
In planking, symmetry is your friend. You can line off only one side of the hull, and do the spiling on that side, get out a plank for that side, and make a mirror image of the plank and fit it to the opposite side of the hull. I noticed only small imperfections in the fit of the mirror image planks, and I corrected them with judicious use of a hand plane. By fitting a complete course of planking, port and starboard, before starting the next course, you are less likely to build in distortions to the hull’s shape.
Next I’ll describe a few things that arise as the planking proceeds.
Staggering butt blocks
All 12 courses of Justine’s cedar planking have butt blocks. Although butt blocks are designed to be very strong and secure, they aren’t as secure as continuous, uninterrupted planks. So it’s important to stagger the butt blocks so that you don’t have a sizable area where the hull is somewhat weakened. There is a rule of thumb in carvel planking that one can follow to suitably scatter the butt blocks: (1) In adjacent planks, there should be at least two frame spaces between butt blocks; and (2) there should be at least two planks separating butt blocks that occupy the same frame space.
Backing out a plank
In most places on the hull, Justine’s frames are curved. The planks lie more or less perpendicular to the frames, and the inside surface of each plank must fit snuggly against the frames. So most of the planks need to be hollowed out slightly, or backed out, so that they will fit well on the inside of the hull where the frames are.
Backing out is done with a hand plane that has a curved iron and a curved sole. I made my own backing-out plane for this purpose using some live oak off-cuts from when I cut out my floors.
I used a standard templating tool to record the convex shape of the frame, and then used that as a guide to how much backing out was needed at each station.
After using the backing-out plane, I lightly sanded the inside surface of the planks but I wasn’t really fussy about eliminating all the planing marks.
One additional note about backing out: the resulting backed-out plank needs to be 5/8″ thick over its complete width after the outside surface is faired, so if a plank needs to be backed out, it must start out thicker than the nominal 5/8″ thickness of the planking. I kept all my planking stock rough sawn until I’d selected a particular piece to use in a particular location on the hull. Once I knew where the piece would be used, I decided how much to plane off. After reducing the thickness, I marked it with the spiled shape. After cutting out the plank’s shape, I did the backing out.
Plank edge bevels
Justine’s plank seams will be caulked with cotton to help make them watertight. Suitable space for the caulking must be left between the plank edges and at butt joints, in the form of a caulking bevel.
I did my best to get adjacent courses of planking to butt against each other, edge-to-edge, as I fit and prepared them for fastening. Then I planed a small caulking bevel along the edge of the new plank I was about to hang, on the edge where it would abut the previously fitted plank. The caulking bevel extended from the outside of the plank to about 2/3 the distance to the inside of the plank (about 7/16″ in this case), and so that there would be a gap of about 1/16″ at the outside of the planking. Before fastening the plank, I put a coat of red lead on both edges of the plank.
Use of leverage
I did most of the planking working by myself. Occasionally I had to come up with alternatives to having another set of hands. A good example was fitting and fastening the last cedar plank at Justine’s transom, where the plank requires a significant twist as it goes aft.
My “third hand” took the form of a wooden hand screw fastened to the plank, then using a line to the barn ceiling to apply sufficient torque to the plank to bring it into contact with the transom. A rolling hitch (which I learned as a “taught-line hitch” in Boy Scouts) came in handy to properly adjust the tension in the line.
Fairing the planks
At this point Justine’s hull has 12 cedar planks on each side. They have been backed out on the inside, but so far the outside of each plank is still flat. Thus, from the outside, the planking is facetted and only approximates a smoothly curved, fair shape.
Fairing the hull is not simple. It needs to be approached slowly and deliberately if you are doing it for the first time. I started with an 03 smoothing plane that was very sharp and set for a very fine cut. I mostly planed diagonally, across several planks. You have to be careful to plane with the grain of the planks, and frequently the grain changes direction so you have to be careful. Places where you have drilled out knots are also difficult because the direction of the grain can change abruptly. It’s impossible not to have a bit of pieces of wood chipping out.
Battens are useful for finding high spots that need planing off, so are you hands: simply stroking a hand along the planking is a good way to detect irregularities. When the hull is fair, at any point on its surface you should be able to lay a batten, in any orientation, and it should lie right on the hull with no gaps.
I finished fairing using a long piece of thin plywood to which I’d affixed handles on the top surface and sandpaper to the bottom. Scot calls this tool an “agony board.” I didn’t use this so much to fair the hull, as to simply remove planing marks once I’d come close to fair-ness with my plane.
As you are fairing the hull, inevitably you reduce the plank thickness to the point where you are about to plane into one of the silicon bronze fasteners. So you have to back out the fastener, counterbore a little deeper, and reinstall the fastener.
Once you’ve done your best fairing the hull, you need to fill any chipped out grain, as well as over all the fasteners—and there in excess of 1000 silicon bronze flat-head screws that secure the cedar planks! I used “Bondo” over the fasteners as I thought it would be easier to dig out than epoxy and microbaloons, if the planks ever need to be refastened. This occupied several day’s work, filling, sanding, and perhaps refilling and sanding. Fortunately my son Micah helped me with this phase of the project.
Caulking
Cotton caulking comes tolled up, somewhat like a skein of yarn. Unlike yarn, it is not twisted but it is formed into a long strand about 1/2″ in diameter. A strand can be divided if less material is needed to fill the seam which was always the case for Justine.
I’d never caulked a seam before building Justine. Two excellent articles on the subject have appeared in WoodenBoat magazine, and I followed the advice of author Harry Bryan very closely. The first, “Caulking Small Boats: Part I. Tools for the Job.” WoodenBoat, Vol. 201, p. 33 , taught me that the best tool by far to use for caulking is a roller that is easily made. I also forged my own caulking iron and made a caulking mallet following a design by Joel White (a drawing appears in Harry Bryan’s article).
I also closely followed Harry Bryan’s advice in his followup article “Caulking Small Boats: Part II. Putting the Tools to Work.” WoodenBoat, Vol. 202, p. 25. It took several seams to get the hang of it, but after that it moved along nicely.
Once all the seams are caulked, they are payed. This involves applying thinned paint to the caulking to help waterproof its exterior surface, rather than to saturate it entirely. That way, if water does get in, the raw cotton will swell and seal the seam. Again, I followed the information in Harry Bryan’s articles to pay the seams.
The final step to finishing the plank seams is to apply seam compound over the payed caulking. This produces a surface over the caulking that is flush with the plank surfaces and also helps waterproof the seams. I’ve been warned that once Justine goes in the water, the planks will swell, and some of the seam compound will be forced out and need to be smoothed off when repainting the hull.