Posted By admin on February 2, 2015
Coronet is being planked from the bottom upwards. We are using white oak both for its strength and it’s ability to bend when steamed. There isn’t a lot of twist at the bow of the boat,
but the stern is another story entirely.
There is a tremendous amount of twist where the hull transitions from vertical at the keel to nearly horizontal.
One way to cope with this transition is to use thinner (in height) planks, called stealers, in the area of the sharpest curve.
Without the stealers, you need a very thick piece of wood to bridge the same gap that could be bridged by two thinner pieces of wood.
In this illustration the dark lines show the thickness needed to span a curve, with the dotted lines showing the final consistent thickness of the plank. The pink lines show the thickness needed for two stealers to bridge the same distance. You can see that there is much less wasted wood with the two plank solution.
Each plank is cut so that there is a solid wood-to-wood connection between them along the mating inner faces.
The angle of the mating faces changes along the length of the plank as the shape of the hull changes. If the boat were shaped like a square box, you could make the edges of all of the planks square (i.e., 90 degrees) and they would fit together perfectly. Since the planks are going onto a curved surface, you have to bevel the edges so that they mate properly. Here’s an illustration.
On the left side you see planks that are fitting up against a curved frame where the mating edges are left square. You can see that only the outer edges touch, leaving a gap on the inside. On the right is an illustration of the same planks, with the top plank’s bottom edge beveled to properly mate with the lower plank. Only the innermost one third of the mating surfaces needs to actually touch. The outer two thirds are opened up to form a caulking bevel.
You can find a nice video of the plank cutting process here.
Here’s a close-up of the caulking bevel.
It’s good practice to set up your work area with all of the tools that you’ll need close at hand and well-organized.
While trunnells are the primary fasteners for the planks, the ends are first locked into place using a pair of bronze hanging spikes. Once the plank is clamped into position, the shipwrights drill two holes into the ends of the plank.
The drill creates a round hole, but the hanging spike is square in cross-section. To avoid splitting the end of the plank, the team first drives a specially formed spike into the hole to square up its sides.
This is driven in just far enough to change the round hole in the plank to a square hole, and then removed.
After this, the bronze hanging spike can be driven in fully.
The hanging spike is driven in below the surface of the plank, and will be bunged over later. A backing out punch is used like a large nail set to help drive the spike in completely.
The ends of each of the lower planks butt up against one another. This vertical seam is called, unsurprisingly, a butt joint.
In order to avoid butt joints in the topside planking, these planks will be scarfed together to form one long, continuous plank. Here Eric is working on the jig that will be used to make those tapered scarf joints.