Backbone

Forging the Keel Bolts

Silicon bronze is an alloy of copper with about 3% silicon. It has excellent saltwater corrosion resistance, high strength and toughness, and develops an appealing green patina after exposure to the elements. Silicon bronze parts can be fabricated by casting (melting the bronze and pouring it into a mold) or by forging (hammering, bending, etc.) the material into the desired shape. When polished, silicon bronze looks quite a bit like gold.

I made quite a lot of my own silicon bronze hardware. The majority of the parts I made were investment cast (the “lost-wax” casting process). I hot-forged a few parts that have simple shapes, including the keel bolts.

Prior to my retirement in 2013, I was Professor of Physical Metallurgy in the Department of Materials Science and Engineering at MIT. One of my accomplishments there was to re-introduce blacksmithing to MIT in 1984. So I had access to MIT’s forge as well as my department’s foundry and machine shops. I also learned a lot from of some of my colleagues, and thereby acquired a pretty good idea what I should be doing. Still, there was a lot of “learning by doing.” This post will focus on how I made my keel bolts. I’ll describe how I cast some parts in a later post.

Silicon bronze rod with its diameter matching the bolt size is used as stock. In the photo below, the somewhat rusted dog-bone shaped item to the right is a heading tool. There are square holes of two different sizes (5/16″ and 3/8″ in this case) at the ends.

For this carriage bolt I used a piece of 5/16″ diameter bronze rod about 15″ long. The heading tool is to the right of the ruler. It’s forged to shape from a piece of mild steel, then holes are hot-punched at each end, using a tapered square punch. The punched holes taper a bit, leaving the square hole a bit larger on the bottom side of the heading tool. The taper makes it easier to insert and remove the bronze rod during the forging operations.

I used a coal-fired forge to heat the very end of the bronze rod to a medium red color. A fan delivers air up through the bottom of the fire and allows it to get very hot (indeed, hot enough to melt steel).

A forge is designed to produce a high temperature and to heat the piece rapidly. Air force up through the fire from the bottom makes for a high combustion temperature, and the moving hot combustion gasses transfer heat to the piece very effectively.

With the end of the rod heated, it is removed from the fire and struck along the rod’s axis with a hammer so as to upset or “mushroom” the end of the rod. This increases the diameter at the end of the rod, to the extent that this part will not pass through the square hole in the heading tool.

The first heat is used to “upset” the end of the rod: you hammer on its end, along the rod axis. This “mushrooms” or upsets the last 1/2″ or so of the rod, giving extra material from which the head of the bolt will be made.

The rod is dropped down through the heading tool leaving the upset end extending a few inches beyond the top of the heading tool, then the upset end is reheated in the forge.

After upsetting the end of the rod, I put the rod through the heading tool before heating a second time. This allows me to move quickly to the anvil and start forming the bolt head, without a delay from having to fiddle with getting the hot piece into the heading tool. I don’t heat the heading tool significantly while the piece is in the fire, but it does heat up some once you start forging hot bronze down into it!

The cold end of the rod is inserted into an oversize hole in the anvil (the “pritchel hole”) and the heading tool is allowed to rest on the face of the anvil. Then the heated, upset end of the rod is struck forcefully with the hammer several times. This serves to both drive some hot metal down through the square hole in the heading tool, and to begin to flatten out the head of the bolt.

The heading tool is at the left on the anvil, and the rod being upset passes through the anvil’s pritchel hole and hangs down toward the shop floor.

It takes me a few heats to finish forging the head of the bolt.

After the first heading operation, the bolt head is starting to take shape and the square “flats” under the head are beginning to form.

When all goes well, after a few heats the bolt head has a slight crown, it’s centered on the bolt shaft, and there’s a nice square at the top of the bolt’s shank, just under the bolt’s head.

It usually takes me at least two heats to fully form the bolt head over the heading tool.

After the forging is completed, the rod can be hammered out of the heading tool from the back side and cut off to give the required length of the bolt. I always did some filing of the square part of the shaft to clean it up and give it nice sharp corners. I usually cut the bolt’s threads using a lathe because it’s quick and I was fortunate to have access to one. I also cut some by hand, using a die of the appropriate size.

A completed 5/16″ x 8″ carriage bolt. When the bolt is installed and snugged down, the square at the top of the shaft gets drawn down into a round hole (in wood or lead) and this locks the shaft of the bolt so it won’t turn as the bolt’s nut is tightened.

Most of the carriage bolts I made were 5/16″ or 3/8″ diameter and fasten through Justine’s keel plank and floors. Eight 1/2″ bolts hold on her lead ballast keel. A few 5/16″ bolts simply fasten the stem and keel plank together.

Keel Plank

With the centerboard trunk, frames, stem, and transom in place, it’s time to work on Justine’s keel plank and thereby complete her backbone.

Scot and I found a suitable white oak plank for the keel at New England Naval Timbers, on the same trip that we got stock for the stem and frames. We picked over an extensive stickered pile of planks that had air dried for a couple of years to find one that was suitably long (over 16′) and straight, not overly wide, and not overly thick. It gave us quite a workout because there were many planks larger than I needed that had to be shuffled around during our search.

The keel plank is white oak, about 9″ wide, 2 1/2″ thick, and over 16′ long. It had been stickered and air dried at New England Naval Timbers. Before unloading it, I gave it a coat of linseed oil and painted the ends with red lead to slow the rate of drying. Scot helped me move it from the trailer to a shady spot up by my barn. It was so heavy I was close to my strength limit just carrying one end.

When in place on the hull, the keel plank is curved enough that it needs to be steamed and quickly clamped in place. Because it is over 16′ long, and my steam box is only about 10′, each end needed to be steamed in separate operations. As noted in earlier posts, the keel plank is bolted to the floors at stations 5–22, and amidships the bolts also pass through the centerboard bedlogs. A slot must be cut in the keel plank so the centerboard will pass through it as it’s lowered and raised. The ends of the centerboard trunk posts fit through the ends of the slot in the keel plank and serve to lock it into alignment both fore and aft and side-to-side.

All ready for the keel plank, with centerboard trunk in place.

Cutting the keel plank to shape

The easiest way to cut and fit a large part like the keel plank is to make a plywood template for it. I used pieces of 1/4″ plywood for the template and began by cutting the holes for the projecting ends of the centerboard trunk posts and clamping it into its curved shape fore and aft. Then I marked the positions of each station on the underside of the template, and from my lofting I took off the dimensions for the widths of the keel plank at each station. By clamping the template stock in place on the backbone, then marking the positions of the stations on the template, I knew that the curvature of the keel plank would be properly accounted for in my template layout.

I’ve made a template for the keel plank, using pieces of 1/4″ luan plywood. I had lofted the keel plank, so I used the lofting to mark the template for width at each station. The keel plank will extend from the transom to the stem, and it has a significant arc. Note how the centerboard trunk posts stick up through the ends of a slot in the template.

I had stored the keel plank stock outdoors, slightly off the ground and under a tarp. It remained there from August 2008 to October 2009 before I was ready to cut into it. So I figure it had at least three years of air drying before I started to use it.

Keel plank template on white oak plank. I’m going to make the first cuts oversize as I’ve still got a lot of material to remove and I don’t know if the plank will distort when the excess is trimmed away.

One can’t predict what internal stresses might be present in a piece of lumber. A plank that is straight might take a significant bend if parts of it are cut away. So it’s safest to make the first cuts so that there is some excess material because then you have a second chance to correct for any bend. I left an extra inch or so along the sides, and did not take any off the ends on these first cuts.

Here’s the oversize blank for my keel plank. It also needs to be reduced in thickness from about 2 1/2″ to 1 3/8″.

At 2 1/2″ thickness, the plank I purchased was nearly twice the 1 3/8″ thickness of the finished keel plank. So I removed the excess by taking many passes through my thickness planer. This is an opportunity to plane off parts of the plank that may have imperfections that are close to one surface or the other. And to a limited extent you can correct any tendency for the plank to bow or twist by using a power plane to bring one plank surface close to flat, then begin taking passes off the other side with the thickness planer.

Running the keel plank through my thickness planer. The planer shavings really piled up.

At this point the plank is the proper thickness, but overly wide and long. After placing the plywood template near the center of the plank I marked out the positions of the centerboard trunk posts and drew lines to mark the extent of the centerboard slot I needed to cut. The most expeditious way to cut the slot is with a circular saw, but I was leery of making the plunge cuts this would require. With a few tips from Scot (plunge very slowly, don’t risk turning the saw and jamming the blade in the kerf), I was confident I could make the cuts safely. Because the saw blade is circular, these blind cuts need to be finished with a hand (rip) saw at the ends. After these cuts were finished, I bored some large holes near the ends of the slot to release the long waste piece in the middle, and I squared up the ends using a large chisel. Finally, I lined up my template with the slot in the plank, and marked the plank for my final cuts of the keel plank’s profile.

I transferred the positions of the centerboard trunk posts from the template to the keel plank and used my circular saw to make careful plunge cuts so I could form the slot for the centerboard to pass through the keel plank. I bored holes to release the material from between the saw cuts, then cleaned everything up with chisels, a rasp, and sandpaper.

Prior to attaching the keel plank, its sides need to be beveled. This is detailed in the lines plan, lofting, and construction plan. In subsequent pictures you will see that the beveling has been done.

Adding the keel plank to the backbone

The keel plank was too stiff to fit to the rest of the backbone without steaming it to make it more compliant. I began by steaming the aft end and clamping it down to set its curved shape.

After steaming the aft end of the keel plank, we clamped it in place around the centerboard trunk, and used an overhead “shore” to get the required bend back toward the transom. I left it in place for a couple of days to cool and set its new shape.

The overhead “shore” is a 2 x 4 that has been cut to an appropriate length so it can be inserted between the barn ceiling (jammed against a joist) and the end of the keel plank. A shingle serves as a wedge to force the keel plank down in place on the transom and transom knee.

Once the after end of the keel plank had been permanently bent, I steamed the forward end. Here you see the curved aft end; the forward end is in the steam box.

After sufficient steaming, the forward half of the keel plank is removed from the steam box and clamped in position at the centerboard trunk while it’s still hot. I used an overhead shore (removed before this photo was taken) to force it quickly into position against the stem, then replaced the shore with the clamps you see here.

The keel plank is fastened to the backbone with 29 silicon bronze carriage bolts of various sizes and lengths. I had pre-drilled all of the floors for the bolts before riveting the floors to the frames. So I was able to drill upward through the pre-drilled holes in each floor, and drill a perfectly aligned hole in the keel plank. (Some extra-long drill bits were required!) Then all that remained was to drill counterbores on the outside surface of the keel plank to accommodate the bolt heads and the bungs that would cover them. (I’ll explain how I made the keel bolts in a future post.)

The keel bolts are all silicon bronze carriage bolts. There are 29 in total. At this stage of construction, 8 bolts are installed temporarily and these are simply suitable lengths of 3/8″ steel threaded rod. These ultimately will be replaced with the eight 1/2″ carriage bolts that hold on Justine’s 1200+ pound ballast keel.

The keel plank has been drilled for its fasteners. The carriage bolts are inserted into the keel plank and pass through the pre-drilled holes in the floors. The holes in the keel plank are counterbored so that the bolt heads can be covered over with wooden bungs. Washers, lock washers, and nuts secure the bolts on the upper side of the floors (upper when the boat is in the water).

After drilling all the keel bolt holes, I removed the keel plank and coated its top side with red lead, except forthe surfaces that will be fastened flush to the stem, bedlogs, transom knee, and transom. Those surfaces will be coated with adhesive bedding compound before fastening to ensure permanent water-tightness. (The adhesive bedding compound adheres better to bare wood than it does to painted surfaces.)

We’ve just put adhesive bedding compound on the bedlog/keel plank mating surfaces, and positioned the keel plank in place. Scot is helping me install the bronze keel bolts as well as some temporary threaded rod. Note the relatively wide bevel on the keel plank forward of the centerboard slot.

The keel plank/stem joint is bedded and ready to bolt down.

After fastening the stem/keel plank joint, there is some extra wood to be pared away. And the stem rabbet needs to be extended back and partway into the side of the keel plank.

Stem/keel plank joint after fairing. The side faces of the stem have been bevelled back to the rabbet line, and the stem rabbet has been extended aft to where it begins to die out along the keel plank. The counterbores for the keel bolt heads have been bunged.

Transom

The Flatfish plan specifies either white oak or mahogany for the transom. I chose mahogany because of its classic look. The transom thickness is 1 1/8″, so I needed to purchase 5/4″ thickness planks from which I could mill and then glue up boards to produce a blank that was roughly 4′ x 5′ in size. I got my planks from Highland Hardwoods in Brentwood, NH.

There are a variety of woods commonly known as mahogany. Two general categories are “Honduras” and “African.” Honduras mahogany is also known as “genuine mahogany;” the so-called African mahoganies are actually different species. Both actually look quite similar, and Justine incorporates both types. To my eye, the main difference is that Hondouras has a more even color, and African tends to have more pronounced lighter and darker bands parallel to the “grain” of the wood. In spite of its “more even” color, Honduras mahogany can have very distinctive grain patterns, as seen below.

My transom planks were about 7″ wide at most, so the transom needed to be made up of 7 planks, glued edge-to-edge. Large glued-up members like this are more likely to resist splitting and warping if the joints are reinforced by embedding metal rods called “drifts” as the boards are being glued up. I used 10 pieces of 5/16″ bronze rod, about 8″ long, driven into predrilled holes that crossed the joints and spanned the planks on both sides of the joints. The holes need to be drilled very carefully so they don’t wander away from the center of the planks, and the drifts need to be placed with forethought so that they will not interfere with any fasteners that go into the transom later in the construction. The planks were glued up using West System epoxy.

The transom blank glued up and being smoothed with my 07 joiner plane.

I smoothed the glued-up transom using a hand plane, followed up by hand sanding. After sanding I applied a coat of shellac to seal the wood and give it some protection from stains.

For finish sanding of the transom I made what I call a “sanding plane” consisting of a piece of 3/4″ plywood to which I attached home-made handles fashioned after those that might be found on a hand plane. The plywood piece was sized to fit a whole sheet of sandpaper. I used two-sided tape to affix the sandpaper to the plywood.

Transom blank after sanding and sealing.

A piece of the backbone known as the transom knee is bolted through both the transom and the keel plank to span and thus reinforce that joint. My transom knee was made from a piece of white oak.

Nearly all of the fasteners that join the backbone members are silicon bronze carriage bolts, ranging from 1/4″ to 1/2″ in diameter. Carriage bolts have a smooth rounded head, and the upper part of the shank, just under the head, has a square cross section. The other end is threaded, and secured with a washer, lock washer, and nut. As the nut is tightened, the square part gets drawn down into the fastener’s (round) hole, preventing the head from turning. In this way the bolt can be fully tightened from one end, without needing a tool to hold the other end. The head of the bolt can be buried below the surface of the wood, and if the bolt becomes loose, it can be retightened simply by tightening the nut.

Carriage bolts are used to fasten the transom knee to the transom. Bolt holes through the transom are counterbored so that the bolts can be concealed under bungs (wooden plugs) on the transom surface. I used a square as a guide while drilling the holes, and a depth gauge to ensure that the counterbores were drilled to an appropriate depth.

The transom knee is bolted onto the inside face of the transom, and will serve to strengthen the joint between the keel plank and the transom. All sides of the transom knee have been give a coat of red lead.

I wanted to carve my boat’s name in the transom and realized that I should do that before securing the transom to the construction molds. This would allow me to do the carving with the transom horizontal, and at a convenient working height.

Justine is named after Justine Liff, who we met while she was Boston’s Parks Commissioner. We quickly became friends with Justine and her family. Sadly, we only knew her for a short time before she became very ill with cancer and died. My wife Annie, an Episcopal priest, presided at her funeral at Boston’s Franklin Park. During the funeral, Boston’s Mayor Tom Menino told the assembled crowd that Justine’s assistant said that she didn’t have to blow-dry her hair, she could just follow Justine around for 15 minutes and the breeze that was created would suffice. This was a good omen for Justine the boat!

Once Justine is in the water, the transom will be tilted at about 45 degrees to any viewer. I factored this into my layout by stretching my letters by about 40% in the vertical direction. After picking out a font and laying out the stretched letters on a slight arc to complement the shape of the transom, I made a prototype carving on a piece of basswood.

I purchased a small set of traditional carving tools for the project. I used a carver’s mallet for most of my carving.

My prototype carving in position on the transom.

After carving my prototype, I made very small adjustments to the letter spacing, then proceeded to transfer the layout directly on the transom. I did the transfer by blackening the reverse of my layout drawing with a soft pencil, then laying it on the transom and tracing over the letters. This gave outlines of each letter on the wood that I could carve from.

I’ve just traced over the letters on the paper layout, transferring them to the transom, and flipped back the layout sheet. The transferred lines are just barely visible in this photo.

Carving workspace. I was able to carve quite comfortably while seated.

I started by carving the straight letters, gradually working up to J, U, and S.

Finished carving. Much later in the construction process, the transom was varnished and gold leaf was applied to the incised surfaces.

The transom/knee assembly in place on the construction molds. I have refined the shape of the transom and roughed out the winding bevels on the edge of the transom. (This photo was taken before “Justine” was carved in the transom.)

Detail showing how the transom knee fits onto construction molds 22 and 23.

With the frames, stem, and transom in place, only the keel plank remains for the backbone to be complete.

Stem

Justine’s stem has a significant curve, and the construction plan shows it as a single piece. In order to have sufficient strength, the grain of the plank from which the stem is cut must align with the stem’s curved shape. So I was in search of a plank cut from a log with a significant bend. In boatbuilding parlance, this is known as a “grown shape.”

Some tree species have lots of branches that are naturally curved. Live oak is a good example. Massive frames for ships like Old Ironsides were cut to shape from live oak branches rather than be shaped by steam bending.

In New England nowadays the most prevalent species from which to seek grown shapes is black locust. I knew that New England Naval Timbers had a good supply of black locust, so I made a plywood pattern of the stem shape and took it with me in my quest for a suitable plank. Scot accompanied me on the trip and we spent the better part of a day inspecting stacks of planks from which I could make not only the stem, but also the frames and keel plank.

We started the search for the stem plank by picking over a very large pile of black locust planks. There were all sorts of shapes, consistent with the naturally curved growth habit of this species. Because of the odd assortment of shapes, the planks could not be neatly stacked. So we spent a good bit of time and energy digging through a sizable pile of very heavy planks. Each one that looked like it might work, failed to conform to the pattern.

Fortunately on the day of our visit, a fresh supply of black locust logs had arrived and was in the process of being cut into planks. Duke Besozzi, New England Naval Timbers’ proprietor, took a look at the pattern, and the pile of logs, and identified one he thought might work and put it through the mill. Voila! I had the plank I needed.

Black locust plank with stem pattern overlaid. The direction of the grain in the curved part of the plank closely matches the shape of the stem.

I made the first cut with my circular saw, cutting slowly so the saw would not bind in the curved cut. The plank was about 2 1/2″ thick, and the capacity of my saw was only 2″, so the cut did not go completely through the plank.

Using a tip from Scot, I drilled a series of holes at about 3″ intervals, down through the kerf of my first saw cut and out the far side of the plank. When the plank was flipped over, I had a nice line of holes to guide a second cut that would meet up with the first one and free the two pieces.

First rough cut of the stem blank is completed. The stem will come from the crescent-shaped piece.

My first cuts were deliberately oversize. I ran the stem blank through the planer and reduced the thickness to 2″, then let the blank age in the barn for several months before proceeding In this way, any distortions during drying could be corrected when the stem was planed to its final 1 3/4″ thickness and cut to its designed profile. The ends of the blank were given a coat of red lead to retard rapid drying and prevent checking (formation of longitudinal cracks that might start from the ends).

The stem cut to its final profile and thickness in place on the construction molds. The bevels on the floors at stations 2–5 match the changing inclination of the stem. A batten is temporarily fastened along the position where planking will be. Plank ends will land in a groove that is cut in the stem, known as the stem rabbet.

The stem rabbet is a “V” shaped channel that provides a landing place for the forward ends of the planking. The position of the rabbet is indicated on the lofting. I cut most of the rabbet with chisels. The wood block seen resting in the rabbet is in position where a plank will terminate and be fastened to the stem. The two facets of the rabbet are cut to meet at a right angle, and the forward most facet is 5/8″ wide, matching the planking thickness.

Floors

The term “floor” when used in describing a wooden boat does not refer to what you might walk on—that would be the cockpit sole or cabin sole (or in Justine’s case, the cuddy sole). Rather, a floor is a key component of the boat’s backbone that serves to tie the boat’s frames into the keel.

Justine has a floor and two frames at each station where there’s a construction mold. Except amidships, in the way of the centerboard trunk, each floor spans the frames where they are almost touching at their connection to the keel (which is high up on the construction molds while the boat is being built).

The floors are all triangular but their sizes vary considerably from station to station. Far forward, the hull has a steep “V” shape, while amidships the angle is much shallower. In addition, the depths of the floors vary considerably. Many of the floors support the cuddy sole or the cockpit sole, and three of them support bulkheads. All of these details are given on the plans.

Justine’s floors are all made from live oak planks. They vary in thickness from 7/8″ to 1 3/8″.

The floor at station 12 is one of the largest, and its top edge is rabbeted to receive the bulkhead between the cockpit and the cuddy. The floor at station 2 is the smallest, and here it’s sitting on top of station 12’s floor.

Fitting a floor

The next series of photos shows how I made a fitted the floor at station 3.

Construction mold 3 ready for fitting its floor. Temporary cleats allow the frames to be tightly clamped against the mold, and a cleat has been added at the correct height for what will be the top edge of the floor. I used a block plane to make a “flat” near the top of each frame so that the frames would fit snugly against the floor.

A blank for the floor is clamped in place on the mold and marked for trimming to size. The cut will be bevelled to match the angle of the frames.

Making the bevelled cut on the band saw.

Each frame is attached to the floor at station 3 with three copper rivets. The beveled cuts on the floor were left slightly oversize so they could be planed to match the frame bevels once the floor was riveted in place.

Riveting

Quite a few of the fastenings in Justine are rivets made from copper nails. The plans indicate where rivets should be used, and what size nail to use. Rivets are used in locations that are not likely to ever need tightening or replacement. The tools I used for riveting are shown below.

A hole that closely fits the copper nail is drilled through the frame and floor. The nail is driven from the frame side, then a copper burr is set over the nail’s point and driven down against the floor using the burr setter.

The pointed end of the nail is cut off using diagonal cutters. The cut preserves a length of nail beyond the burr so the rivet can be headed over the burr. A length of about 1.5 times the nail diameter is left for forming the rivet head.

The part of the nail that protrudes beyond the burr is struck repeatedly with a ball-peen hammer and this flattens and rounds over the end of the nail, forming the rivet head.

The bucking iron is placed firmly against the nail’s head, then rapid light taps with the ball-peen hammer are used to “upset” the nail and form a rivet head that fits tightly against the burr and overlaps it.

Limbers

My father-in-law Sandy once questioned my desire to build wooden boats by telling me: “Wooden boats leak.” That didn’t deter me. Rain water also can get into a boat (even one made of fiberglass!). To deal with the inevitable accumulation of water, the hull must allow for draining any water that accumulates to the lowest point of the hull, where it can be pumped out as necessary.

Because of their placement in contact with the keel plank, floors are barriers to fore-and-aft flow of water in the hull. “Limbers” are passageways that allow water to move past each floor and thereby collect at the lowest point in the hull, in Justine’s case between stations 12 and 13, beneath the forward end of the cockpit sole.

Floor at station 12. A 1″ hole has been bored to allow water to move aft to the low point of the hull. There are two keel bolts at this station, positioned symmetrically about the limber. The frames at each station are trimmed to match the bevel at the base of the floor, as seen here.

Midship floors

The centerboard trunk intersects the floors from station 13 to station 17, so the floors are altered to accommodate it. Keel bolts will pass through the keel plank, bedlogs, and floors at these stations, and limbers are placed outboard of the bedlogs.

From stations 13-17 the floors need to accommodate the centerboard trunk. At station 13 only the forward tip of the trunk intersects the floor and the floor extends from port to starboard. The trunk is much deeper at stations 14-17, so at each of these stations there is a starboard floor and a port floor. Limbers will be cut in floors and frames adjacent to the centerboard trunk bedlogs. (The floor at station 14 is aft of the construction mold, a detail shown in the plans.)

I made and installed Justine’s floors between August and November 2009.

With the frames and floors in place we’re ready to make Justine’s stem and transom and add them to the backbone structure.

Frames

Justine has a pair of frames (one port, one starboard) at each station where there is a construction mold. This makes a total of 44 frames, two at each station from stations 2–23. The frames are cut from white oak planks and milled to 7/8″ square cross section. They are steamed, quickly bent to shape on the corresponding construction mold, clamped in place, and allowed to cool and harden for at least a day or two.

I bought most of my white oak from New England Naval Timbers in Cornwall, CT. The planks are “live edge,” that is they are complete cross sections of logs and often have bark on the edges of the planks. (Sometimes the bark is loose and falls off when the planks are first cut.) White oak can have a significant layer of sapwood under the bark, and it is relatively unsound for boat timbers. So the sapwood needs to be cut away. (It makes good kindling.) The planks I bought had been stacked and “stickered” with wood spacers, then air dried for at least one year.

If a piece of wood is bent sufficiently, it will break—even if it is steamed. Breaks tend to follow the “grain” of the wood. So frames need to be cut parallel to the grain of the plank in order to minimize places where the grain crosses the frame. Ideally the frames are gotten out of quarter-sawn planks with very straight grain, but it’s hard to find such planks and they are expensive. So I ended up cutting somewhat curved shapes for my frame blanks, following the grain of each plank.

A 4/4 white oak plank from which I’ll cut some frame blanks. Here I’ve cut off the lighter sap wood because it is weaker and lacks decay resistance when wet.

After removing the sapwood, I ran the plank through my thickness planer to bring it down to 7/8″. I then marked and cut strips about 1″ wide that followed the grain of the plank. I made these cuts with an 8″ circular saw.

I’ve rough-cut pieces from the plank, following the grain of the wood as much as possible. The pieces are run through the thickness planer to smooth the cut surfaces and bring them down to the desired 7/8″ square cross section.

I sorted my frame stock to match particular pieces to particular station molds. In places where the frame would need to take a sharp bend, I used stock with very straight grain where the bend would be. I tried to use all the stock with more questionable grain for the relatively straight frames on the forward construction molds.

Construction molds 2–11 with their frames cut to size and ready to go in the steam box.

My steam box takes about an hour to really get going. Inside the long box are some cross pieces that serve as racks to separate pieces being steamed. I usually steamed about 8 frames at a time. They were all marked with their mold number, but it was still important to know which frame you were about to grab from the box.

The common rule of thumb for time in the steam box is one hour for each inch of cross section of the piece. So I steamed my 7/8″ frames for at least one hour.

My steam box is made from pine planks about 10′ long. Pictured are two propane tanks, a boiler (repurposed somewhat rusty outboard motor fuel tank) sits atop a burner from a deep-fat turkey fryer, and a Weber grill that is not part of the steaming setup. A length of black plastic pipe delivers steam from the boiler to the middle of the steam box. A hinged door at the end closest to the barn is where pieces are loaded and unloaded from the box.

It is primarily the heat, and not the steam per se, that makes the wood pliable. So it is critical to work quickly once the frame comes out of the steam box. If the frame cools much before being fully bent, you risk it breaking. And, the thinner the piece, the more quickly it cools.

I’ve just removed a hot frame from the steam box and already closed its door. Gloves and a long-sleeve shirt protect me from getting burned.

I fashioned U-shaped straps from steel sheet and screwed them low down on each “leg” of the construction molds. These served to secure the end of the frame very quickly before starting the bend. Extra room was left to drive in a wooden wedge to firmly hold the end of the frame in place. Where the construction molds have a winding bevel, the hot frame needs to be twisted so that it will lie flat on the bevel. Extra hands are needed to clamp the frame in place on the mold.

The construction mold is temporarily attached to the barn floor, and the hot frame is dropped into a sheet-metal strap down near the floor and secured with a wooden wedge. Then the frame is coaxed into conformance with the construction mold. A helper (Scot in my case) assists by securing the frame to the mold with several clamps.

Sliding-bar clamps are used to hold the frame in place on the mold while the frames cool.

I made “dogs” from steel spikes. They have a shallow “U” shape and the pointed end is driven into a pre-drilled hole in the construction mold, leaving space for driving a wooden wedge to force a tight fit between the frame and mold. I occasionally used a dog or two to clamp a hot frame, but more often used sliding-bar clamps. Once cooled sufficiently, bar clamps were replaced by dogs and wedges. This freed up clamps to use for clamping newly-steamed frames.

With a total of 44 frames to steam and bend, you begin to acquire experience to the point that things go relatively smoothly. Even so, getting each one bent and clamped without breaking is a small triumph. I think I broke about five of them and had to cut and steam-bend replacements.

Molds 15–23 with their frames secured in place with home-made metal dogs and wooden wedges.

The backbone of a traditional wooden boat consists of the keel, stem, transom, frames (“ribs”), and floors. All these parts need to be in place on the construction molds before the hull’s planks are “gotten out” (cut to shape) and fastened. The backbone must be suitably strong and stiff so that the boat can withstand large forces imposed by wind and water. The butt of Justine’s mast connects to the backbone at the mast step, and a significant fraction of the forces produced by the mainsail and jib are transmitted to the hull via the backbone.

Components of the backbone should also be resistant to decay from moisture. Traditional wood species that are found in New England with the requisite properties are white oak (Quercus alba) and black locust (Robinia pseudoacacia), and I used both in Justine’s construction. I was extremely fortunate to obtain a supply of live oak (Quercus virginiana, not indigenous to New England) via my neighbor Scot Smith. The source was quite amazing: it had been excavated from an abandoned holding pond at Charlestown Naval Shipyard in Massachusetts! Some of this store of wood even ended up being used in the restoration of Mystic Seaport’s whaling ship the Charles W. Morgan. By the time I got my planks they had been re-sawn to 4/4 and 8/4 (1″ and 2″, respectively) planks and had about 2 years to air dry.

Building Justine’s backbone took me about 2 1/2 years, starting in January 2008 when I milled and glued up the mahogany planks for her transom and ending in July 2010 when the keel plank was bolted to the stem, floors, centerboard, and transom knee. Covering all this will take quite a few posts. In this one, I’ll simply show a few pictures that identify the major backbone components as some readers may not be familiar with the terminology.

The stem is the forward-most member of the hull. Justine’s stem consists of a single piece of black locust. Cleats on the barn floor hold the stem head in position, and construction molds 2–5 are beveled to support it.

Justine’s frames consist of 7/8″ square pieces of white oak. Heating in a steam box makes them pliable. After steaming, they are quickly clamped in place on the molds and allowed to cool. The clamps are subsequently replaced with metal “dogs” until the hull planking is in place.

Justine’s floors are made of live oak. They are triangular in shape and serve to connect pairs of frames at each station. Bolts through the floors tie the frames and keel plank (and/or stem forward, as seen here) together. Three copper rivets secure each frame to its corresponding floor. Here you see the frames with their floors at stations 2–5. Also seen are “dogs” and wooden wedges that hold the frames against their molds prior to planking the hull.

The transom is the after-most member of Justine’s backbone. Justine’s transom is positioned at about 45 degrees to horizontal. I carved her name in the transom while it was still horizontal and at a comfortable working height.

Justine’s keel plank is cut from a 16-foot piece of 8/4 (2″ thick) white oak. It is bolted to the stem forward, the transom and transom knee aft, and the floors and centerboard bedlogs in between.

In future posts, I’ll describe each element of the backbone construction in greater detail.