I purchased four 5/4 Honduras mahogany planks, each 12′ long, to use for the sheerstrakes. Because the finished sheerstrakes are about 22′ long, I knew I would be making each of them up from two pieces of lumber. I planed the planks to slightly over the sheerstrake’s 1″ maximum thickness before cutting them to the spiled shape. This left a bit extra for rounding and sanding the thickest part of the sheerstrake.
Sheerstrake lumber ready to transport from Highland Hardwoods in Brentwood, NH to Georgetown, ME.
I decided to do most of the shaping of the sheerstrakes by hand. But I did use my circular saw to make long parallel grooves of appropriate depth at about five locations spaced at fixed distances from what would be the sheerstrake’s top edge. This would give me reference lines that would indicate when I was getting close to planing off most of the unwanted material, after which I could start working toward a smooth and consistent final profile.
I start to shape the sheerstrake by making lengthwise cuts at a fixed distance from the top edge, with a depth that left nearly what the final height of the finished sheerstrake will be. I made about 5 cuts at key points on the profile to serve as guides when I planed and scraped the profile to its final shape. In this photo I’ve already planed the bottom portion of the sheerstrake to its final 5/8″ thickness.I’ve removed most of the material that I can reach with my smoothing and backing-out planes, but the profile is still a little rough and there are still some traces of the saw cuts I’d made.
I did all of the final shape refinement using a cabinet scraper that I’d filed to an appropriate shape. Using the scraper was a slow process, but very effective. It’s important to keep the scraper very sharp and to scrape “with the grain.” (I found it necessary to shift directions as the grain in some of my planks changed.) Early on, I fitted my scraper with a small piece of wood that hung down over the top edge of the sheerstrake to act as a fence that would ensure that the molded profile maintained a fixed distance from the sheerstrake’s top edge.
I did the shape refinement with a cabinet scraper (on workbench) that I filed to a shape that would produce the designed molding. Early in this process I fitted a small piece of wood (not shown here) on the end of the scraper to act as a “fence” so that the molded shape would accruately follow the upper edge of the sheerstrake.
As illustrated on the Flatfish construction drawing, the molded profile gets somewhat thinner approaching the transom and stem. That required carefully planing off some more material, and doing some additional hand scraping and sanding. With all the hand work, I was glad I’d decided to make the sheerstrakes out of mahogany rather than oak (an option on the construction plan)!
Forward section of the sheerstrake, fitted and clamped in place.Half of the sheerstrake, molded, sanded smooth, and given an initial coat of varnish. There is a significant curve, but once clamped in place it is a very good fit!
Once the forward section of the sheerstrake was shaped and fitted against the adjoining cedar plank, I made the aft piece using the same method.
The two halves of the sheerstrake would need to be joined together with a scarfed joint. Anticipating this, I left extra material to remove near the scarfed ends when I created the planks’ molded shapes. I laid out the scarfs with an 8:1 slope, rough cut them on the bandsaw, then overlapped and planed them simultaneously with my 07 joiner plane. This method ensures a very close fit of the scarfs.
I left extra material at the ends of the molded planks I’d be joining together, then planed scarfs at an 8:1 slope in preparation for glueing the pieces together.Scarfed ends placed to overlap. Extra material in this area will be planed off once the pieces are glued.
With the two pieces scarfed and ready to glue up, I needed a method to get them properly aligned so that the long continuous piece would fit properly against the adjacent cedar plank. I decided to use the spiling batten to draw the plank’s shape, from 6′ forward of the scarf to 6′ after it, on a board about 12′ long, then clamp the two pieces together and glue them directly on the marked board, aligned with the line I’d drawn on the board. I used epoxy thickened with silica to bond the pieces together.
After careful alignment with the lines on the board underneath, the two halves of the starboard sheerstrake are glued together.
After joining the two halves of what would be Justine’s port sheerstrake, I finished refining the molded shape around the scarfed joint. I also marked a second set of mahogany planks to make the starboard sheerstrake.
I did all of the work on the sheerstrakes working alone, including fastening them. I found that the best way to clamp them in position was to start amidships, and add clamps working forward and aft from there.
I hung the sheerstrakes working alone. I clamped the plank in place amidships and supported the stern end with a line attached to the barn ceiling, then clamped it position amidships, and proceeded to place clamps working toward the stem and stern.
The sheerstrake’s forward end fastens into the top of the stem rabbet, so that end needed to be trimmed into the appropriate shape. Once that was done, with the sheerstrake clamped in position along its entire length, I put a piece of tape across the sheerstrake and its adjacent cedar plank near the amidships clamp, to serve as a reference mark for fore-and-aft positioning of the sheerstrake when I started fastening it in place. In the process of fitting and trimming the sheerstrake, I clamped it in place, marked it, and removed it numerous times. Eventually, it was ready to fasten.
I’d very carefully clamped the sheerstrake into fore-and-aft position so that the forward end would lie properly in the stem rabbet, then placed pieces of tape across the joint with the adjacent cedar plank amidships, where I would begin fastening. Clamps came off, the plank straightened out, but I was certain the plank would be properly positioned when the pieces of tape were aligned. In this photo, I’ve just started driving fasteners, working aft.
All the sheerstrake’s fasteners are counterbored at least 1/4″ or so in order that they can be covered with mahogany “bungs” and concealed. And, as indicated on the construction plan, some of the fasteners are only temporary, as after the hull is turned over they will ultimately be replaced by copper rivets that also hold the sheer clamps in place.
All the sheerstrake fasteners have been driven except those that go into the stem. There was sufficient twist between station 2 and the stem that I concluded it would be best to steam that section before driving the screws to bring it all the way down into the rabbet.
I was reluctant to fasten the sheerstrake into the stem rabbet at this point because it took a lot of force to bring it into position with clamps. I decided it should be steamed before fastening, and I didn’t do that until after the hull was painted and Justine was right-side up and outside the barn. I also waited to caulk the entire sheerstrake joint until after the sheerstrakes were completely fastened.
Planking completed! A major milestone!
I began planking by installing the garboards in August 2010, and finished installing the sheerstrakes in May 2014.
A key design feature of many Herreshoff boats is a bright-finished (varnished) sheerstrake with a molded shape that is both visually pleasing and functional as a rub rail. Making the sheerstrake is the most challenging part of the planking: The molded shape changes along the sheerstrake’s length, and the nonuniform cross section complicates the spiling process.
The Flatfish construction drawing includes a full-size drawing of the sheerstrake shape amidships and the shape it takes as it approaches the stem and transom. Also included are the sheerstrake widths at the stem, station 14, and the transom. I used the width information for the sheerstrake when I lined off all the planks.
Sheerstrake profile and width information is provided in the Flatfish construction drawing. I added a few measurements of my own on the drawing.
When spiling a plank of uniform cross section, one uses a spiling batten of uniform thickness. If you were to use a uniformly thick spiling batten for the sheerstrake, and make the sheerstrake to the spiled shape, it would not fit. Maynard Bray’s book How to Build the Haven 12 1/2 Footer provides a spiling method that allows for the sheerstrake’s nonuniform cross section: use a spiling batten of nonuniform cross section approximating the sheerstrake’s molded shape. Specifically, one makes a batten from two pieces, one thin and wide and the other thicker and narrower and placed where the thicker part of the actual sheerstrake is.
I decided to first place the thin, wide spiling batten in place on the construction molds, then bend the 5/16 x 3/4″ piece into place onto the wide spiling batten. With the two pieces in place on the construction molds, I fastened them together with screws, placed near each of the station molds. Then I proceeded to use my dividers and mark the spiling batten for the sheerstrake width at each station.
I made a special spiling board for determining the shape of the sheerstrake. I added a piece of fir about 5/16 x 3/4″ in cross section, positioned about where the thickest part of the sheerstrake would be, to a wide 1/8″ thick piece of cedar.
Because I bent both pieces of the spiling batten into place before fastening them together, I built in some residual bending stresses. When I removed the batten from the molds, it came off with a significant bend and some twist.
After removing the sheerstrake spiling board, it had a significant curve due to uneven bending stresses in the two pieces.
I proceeded to clamp the spiling batten down flat onto my planking stock, then transfer the marks representing the plank widths at each station. I was not 100% confident this method would work, so I first made a “test” sheerstrake from a piece of cedar. This involved cutting out the spiled shape from a 1″ thick piece of cedar, then planing away enough of the plank to give it a good approximation of the molded sheerstrake’s shape.
I’ve clamped the spiling board down flat onto a piece of cedar, from which I’ll make a test piece of sheerstrake to verify that my spiling method will work.
When the test sheerstrake was clamped in place on the molds it fit extremely well, so I was confident that using my spiling on mahogany planks would give me sheerstrakes that would fit.
I wasn’t sure my spiling would be accurate, so I made my first attempt at a molded plank from a piece of cedar rather than to risk ruining a piece of mahogany. The cedar test plank fit very well, so I proceeded to use my spiling to lay out the mahogany planks.
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.
Not all joints where the butt blocks are placed are visible in this photo, but you can get an idea of how they are distributed about the hull.
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.
My backing-out plane, tilted on its side to show the curvature of the plane’s sole.
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.
A plank that has been backed out. The templating tool gives a sense of the curvature at this particular location on the plank. The plane in the photo is not my backing-out plane.
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.
On occasion, a “third hand” was needed to get a plank into position for fitting, drilling for fasteners, and fastening. A method that worked well aft was to use a hand screw applied to a plank that had extra length, then use a line to apply torque to bring the plank into position against the transom.Uppermost plank after fastening and trimming off most of the excess. Note that I used plywood panels to protect the transom during much of the building process.
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.
Cotton caulking is a bit like yarn, but not twisted. It can be divided to make thinner strands of material.
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).
The quickest method for caulking is to roll it into the seam with a tool like the one on the top. A caulking iron, below, is essential in tight spaces. Mine has a radius of about 1/32″ on the edge.I love Joel White’s mallet design. Mine has a curly sugar maple head and a black locust handle.
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.
I’ve come to the end of a strand of caulking and will lightly twist another piece about 4′ long onto this one, then continue to roll it in. This photo allows you to compare a caulked seam with an uncalled one.A completed section of caulking, including a butt between planks. Plank fasteners have been filled with Bondo and sanded smooth.
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.
Every plank’s shape is determined through the process known as spiling. A long, thin piece of wood, narrower than the plank to be gotten out, is clamped in place on the construction molds. It is positioned between the adjacent plank (or keel, in the case of the garboard) and the pencil lines that mark where the new plank’s other edge will be. I had several pieces of cedar that I’d planed to about 1/8″ thick that I used repeatedly as spiling battens. I sometimes used strips of 1/4″ plywood to make up segments of a spiling batten.
I’ve clamped the spiling batten in place where Justine’s third plank on her port side will lie. The spiling batten is narrower than the resulting plank will be, but it is shaped so that when clamped down, it will follow any curve the plank needs to take. I made my spiling batten up from several shorter pieces, joining them with thin pieces of wood, well fastened with several very short screws. By using several pieces to make the spiling batten, I could make slight “dog legs” at the joints so as to follow the curve the new plank would need to take.
Spiling is a clever technique that involves placing marks on the spiling batten that can be transferred onto the planking stock to give the plank’s true shape. Because the spiling batten is thin, it can be bent and twisted so that it lies in place against the frames, then when the batten is unclamped and laid flat, it can be used to mark the planking stock while it is flat. This assures that when cut out and bent into place on the frames, the new plank will fit quite well.
With the spiling batten clamped in place, a pair of dividers is set at a suitable distance (here about 1″) and maintained at that distance for the remainder of the spiling process. I’ve put one leg on the edge of the adjacent plank, then I’ll mark the position of the other leg on the spiling batten.The dividers are repositioned so that one leg rests on the pencil line (made during lining off, not easy to see in this photo but more visible in the previous one) indicating where the new plank’s edge will be. Then a mark is made on the spiling batten where the divider’s other leg falls.The batten now has two points marked. The upper one, marked “K,” is for the edge of the plank that will be closest to the keel, and the lower one, marked “S,” is the edge closest to the sheerstrake. Note also that I’ve put a line on the batten indicating the location and orientation of the station at which the marks have been made.
I marked the spiling batten with “K” and “S” points at every station. Once that’s done, the spiling batten is unclamped and placed on a suitable piece of planking stock.
The spiling batten has been laid on a suitable piece of planking stock, and is held in place with spring clamps. On this particular spiling, I had made a pattern piece that closely fit the shape of the stem rabbet and attached that to the forward end of the spiling batten while it was still in place on the construction molds.With the spiling batten in position, all of the station lines and “K” and “S” points can be transferred to their appropriate positions on the planking stock.I’ve removed the spiling batten, and clamped a batten along the line of “K” points that define the edge of the plank closest to the keel. Then I used a pencil to mark that line on the stock. I also marked the shape where the plank will lie in the stem rabbet by tracing along the edge of the piece I’d added to the spiling batten. Once the “S” points are similarly connected with a smooth curve, the plank can be cut out.After fine-tuning the plank’s shape, the plank is fastened to the frames and along the stem rabbet.
All this may sound complicated and like a lot of work. But you have to do enough of it that you eventually get pretty good at it.
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.)
Bruce Tweedie delivered my planking stock. 600 board feet was more than enough for Justine’s planking.
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.
I stored my planks upstairs in the barn, sorting them into two piles. One was for planks that were nearly straight, the other was for planks that were curved. Here you see the curved pile.
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.
This plank has quite a few 3/4″ bungs installed. There are still a few knots in the foreground, but these are small, tight knots that can be left undisturbed. I haven’t yet trimmed the bungs flush to the plank surface.
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.
The garboard’s shape has been marked on a suitable piece of planking stock, and it’s been cut out using my circular saw.
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.
Before fastening a plank the mating surfaces on both the frames and the plank are given a coat of red lead paint. It’s the only opportunity to get any paint in those joints.
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.”)
The garboard is fastened to the frames with silicon bronze flat-head wood screws. Two screws secure the plank at each frame. Note the pronounced twist in the garboard once it’s fastened in place.
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.
The port garboard butt block ready to bed and fasten.
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.
The butt block is coated with bedding compound before being set in place. Excess bedding compound gets squeezed out once the six fasteners are driven home.Six fasteners do a good job of drawing the plank ends tightly in place so that the plank adopts a curved shape, even close to the joint. The butt block is wider than the plank so that the next plank can also be bedded to it, furtheer ensuring that the joint will be watertight. When the hull is finally right-side up, the curved edge of the butt block will be able to drain any water that might find its way there.The garboard is in place from Justine’s stem to the transom. The butt block is between the second and third frames from the right.
With the port and starboard garboards in place, “only” 24 planks remain to be gotten out and hung…
Justine’s plans do not give any information about the planking, save for specifying the plank thickness as 5/8″ and providing a full-size drawing of the molded sheerstrake’s cross section. I had to turn to a variety of resources to decide how many planks I would use on each side of the hull, and what the plank widths would be along the entire length of the hull.
One useful resource was Maynard Bray’s book How to Build the Haven 12 1/2 Footer, which describes building a smaller, but very similar version of the Flatfish. The book includes a table of plank widths at several stations, and indicates that the Haven was built with 10 planks on each side of the hull. I did a simple calculation: I measured the total width of the 12 1/2 Footer’s planks amidships, and also the total width of what would be needed for Justine’s planks amidships. Justine’s total width was about 30% larger, so I decided I’d use 13 planks on Justine.
I read several books about general principles for lining off planks. An important factor concerns the need to “back out” (give them a concave shape, which I did using a home-made plane) the inside of planks that fit over frames that are curved. Generally, the higher the curvature of the frame, the narrower the planks should be. Otherwise you would need to begin with overly thick planks in order to provide enough material to end up with a curved plank that was 5/8″ thick over its entire width.
In addition, even if the hull were flat, you would not want to make the planks too wide. Wood absorbs and releases moisture to adjust to its environment. It swells as it absorbs it, and shrinks when it dries out. A wide plank that is firmly fastened down can generate high internal stresses as it swells and contracts, and excessive stresses can cause the plank to crack. Narrower planks with caulked seams that are not too tight leave some “wiggle room” for the planks to take on moisture when the boat goes in the water, and dry out some when the boat is hauled out for the winter. (Plywood planking is much more dimensionally stable, so if a boat is constructed with plywood planks, the planks can be wider.)
So one needs a rule about the maximum width of a plank, and a suggestion I had recommended that planks be no wider than 8 times the plank’s thickness. For Justine, that meant no plank should be more than 5″ wide.
Because the girth of the fitted planking is largest amidships and decreases toward the bow and stern, the planks need to taper in width as they approach the ends of the hull.
With these guidelines, I began to line off the planks on the frames using pieces of string so that the lines would be plainly visible and easily adjusted to take fair curves.
I did my lining off with pieces of string attached to nails I placed in the construction mold at Station 23 and stretched to attachment points at the bow. In between, the positions of the strings were easily adjusted to conform to the guidelines I’d decided on. The planks are narrowest at the most highly curved part of the hull, known as the “turn of the bilge.”
The position of the sheerstrake’s top edge (on which the decking rests) was marked very clearly when building the construction molds: the top edge of the “cross spall” on each mold was placed at the sheer line. So in lining off the planks, you are deciding how to divide the distances between the keel plank (or stem far forward) and the sheer line into 13 segments of unequal width.
Forward, the planks end at the stem or keel plank. To avoid placing nails in these backbone members to secure the strings, I simply used pieces of sticky duct tape. I also used my longest battens (about 23′) as guides for fine-tuning the planking lines as I laid them out.
Even though a carvel-planked hull is smoothly curved, because the plank seams are caulked, the plank seams generally remain visible and become a significant feature of how the boat looks. So not only do the individual lines need to be fair, they need to be visually pleasing as a set of not-quite-parallel lines. Ideally, the entire set of lines needs to be “eye sweet.”
Once I was satisfied with the way the strings looked, I made pencil marks where each string crossed a frame. I removed the strings and used a batten to fine-tune the locations of the marks so that each plank edge would be very fair. I completed the lining off in July 2010. I finally was ready to “get out” some planks and “hang” them!
With Justine’s backbone completed, it’s time to start covering the frames with planks and make a watertight hull.
A lot goes into getting the hull planked. First, you must determine how many planks will go on each side of the hull, and how wide each plank will be. This is called lining off the planks. Once you know where each plank will begin and end, you have to determine the shape of each plank by a process called spiling. Small adjustments to the shape are made with a hand plane to get a close fit with adjacent planks.
Each plank’s shape must conform to the curvature of the frames on which it lies. So each plank needs to be planed on its inside surface accordingly: mostly, this means that the planks need to be concave on their inside surfaces. The process of making the inside surfaces concave is called backing out the planks.
Justine’s planks are as long as 21′. The planks in my pile of planking stock ranged from about 11’–14′. So most of Justine’s planks consist of two pieces of planking stock, joined end-to-end with pieces called butt blocks.
All but the uppermost plank that is closest to the deck, called the sheerstrake, are made from northern white cedar (Thuja occidentals), also known as arborvitae. These planks are 5/8″ thick. Justine’s sheerstrake is made of mahogony, and it is effectively a molding with a cross sectional profile that has a maximum thickness of 1″.
While the inside surface of the planks is generally curved, I left the outside surfaces flat until after the planks were fastened. The immediate result is a faceted exterior hull surface. The entire outside of the hull needs to be made smooth and fair. I did this by starting with a hand plane, then finishing with sandpaper.
Once the entire hull is smooth and fair, the seams between the planks get caulked with cotton to impart watertightness to the hull. Then the hull gets painted.
I’ll cover all these topics in more detail with subsequent posts. In the meantime, here’s a photo showing Justine’s planked hull shortly before turning her over and starting to build out her interior.
After completing the planking and applying paint and varnish, Justine’s beautiful shape (thank you, Nathaniel G. Herreshoff!) is revealed. There is still A LOT of work remaining to complete the inside of her hull.
