Fitting the Mahogany Layer on the Palm Beach 22

Our final layer of planking will run longitudinally to look like traditional carvel planking in this build.  That’s where the longitudinal mahogany planks are laid edge to edge and screwed to the underlying frames.  When it’s complete, you end up with a very smooth, fair hull with seams so tight you can’t even feel the transition from one plank to the adjacent one.  Well, that’s the ideal, anyway.  These boats worked because the seams tightened up after the boat was in the water a few days–tight enough to keep most of the water out.  And while it’s helpful to remember we’re building a boat and not a Steinway piano, with a little know-how and patience, we can get reasonably close to that ideal.  We’re going deep into the weeds in the next couple of posts so bear with me.

Now that the first three layers of planking have been applied and faired, it’s time for a few decisions.  We need to decide where to start with the final layer, and how many strakes we need to cover the various parts of the boat (i.e. topsides, bottom, and transom).  Nelson Zimmer gave us some hints about the latter when he detailed the seam battens on his drawings.  Typically planks on this type of boat are about 4 1/2 – 6 inches wide and somewhere around 3/4″ thick.  Our final layer is only 3/16″ thick, but the same principles apply.

So we have some measuring to do.  You’ll notice in this picture that there are vertical lines at intervals along the hull.  I take girth measurements of the bottom and side of the boat at each station and record these measurements in a table.  Then divide these lengths evenly and this gives you the ideal plank width at each station.  I’ve decided on six strakes to cover the topsides from chine to sheer.

Where to start is dictated by how we want the seam overlaps to work at the chine and transom.  We’ll start on the topsides so we can trim the final plank flush before overlapping the bottom plank at the chine.  The bottom plank is  then trimmed flush to the outside of the topside plank.  Likewise, the bottom overlaps the transom and the transom overlaps the sides.  So the order will be topsides, transom, then bottom.

Start by drawing the sheer line along the sides of the hull using a jump stick riding along the top of the sheer clamp (which of course is the bottom edge since the hull is upside down).  The edge of our first strake will lie along that sheer line.  Actually, we want to overlap it by 1/4″ – 1/2″ so we can trim it even with the top of the clamp when we flip the boat.  Now our dilemma is how to transfer that line and its beautiful, fair curve to a flat plank that will lie perfectly against the hull in the shape we want.  That’s a tall order.  Once you have successfully laid out this line on your plank blank, you may be surprised at how much of a curve you need.

Well the answer is an old boatbuilding skill called spiling.  Take a flexible, but stiff enough piece of lumber — I use cheap, 3/16″ plywood from my local lumberyard.   Lay it along the hull and rough out the curve and cut it to that curve.  Now lay it back on the boat, starting in the middle of your run and tacking or clamping it along the hull about an inch or two up from the sheer line.  Make sure to let it relax naturally against the hull, being very careful not to introduce any edge-set.  If you force it, you’ll notice a hump will pop up a few feet from you.  It’s got to lie perfectly flat along the hull for its entire length.  This may take a few trips back and forth to the saw to trim it up a bit.  Now clamp it well and using a compass, or a block, trace a line parallel to the sheer on your spiling plank.  Also transfer all of your station lines to it.  Remove the spiling plank from the boat.  Put it on your plank blank, and trace along the line using your compass to transfer the sheer line to your plank.  Carefully mark all your station lines as well.  Cut outside this line, leaving a 1/2″ margin.  Lay the plank against the hull and see how you did.  When you’re satisfied, lay out the widths from your table at each station line and using a batten, mark a fair line for the top edge of the plank.  Carefully cut along the top edge and dress to the line with a hand plane.  Make sure the top edge is perfectly fair, with no humps or hollows before you attach it to the boat or you’ll drive yourself mad trying to fit the next plank to an unfair edge.

Depending on the length of your planking stock, with a 22′ boat, and the curves forward, you’ll need two or three lengths to get from stem to transom.  If you’ve made it this far, trimming nice tight butt joints in your planks will be child’s play.  Trim the first plank in a straight line with a good sharp saw.  Overlap it on the following plank and scribe the line.  Then cut it and dress it up with your hand plane.

With the first strake fit and clamped in place, drill some locator holes that you can screw through when you’re gluing so you can get that plank back in the exact location you’ve struggled so hard to make it fit in.  The rest is rolling on the glue and creating an unholy mess before you get everything situated just right and feel comfortable walking away for the night.

But just before you do, clean that top edge as clean as a whistle so you won’t spend the entire next day carving away dried squeeze out glue.  You’ll need that nice clean edge when you start fitting the next strake.  Cheers!

If you have more than a casual interest in spiling, you can find many good sources to consult.  I recommend How to Build a Wooden Boat by Bud McIntosh.