Chris Cameron PhotographyAn oval coaming that transitions into the cabin sides, combined with sprung teak deck planking, lends an air of elegance to the Dark Harbor 17 1⁄2 KOTIMANA. She was built at the Northwest School of Wooden Boatbuilding in Port Hadlock, Washington.
The first phase of the Dark Harbor 17 1⁄2 project at the Northwest School of Wooden Boatbuilding involved building KOTIMANA’s hull and deck on two separate construction jigs. This took about four months and was recounted in Part 1 of this series. After the hull and deck structure were successfully fastened together and the final four strakes of planking were hung, the students got to work preparing to build the deck, coaming, cabin, interior, and spars and also to install her rigging and hardware.
The original 1908 plans for the Dark Harbor 17 1⁄2, designed by B.B. Crowninshield, called for the deck to be built of tongue-and-groove white pine sheathed in canvas, which in those days was typically bedded in white lead paste. KOTIMANA’s owner, however, requested a deck of teak planking glued over a subdeck of 3⁄8″ okoume marine plywood. This method of construction not only provided better strength than the original but also gave the boat the incredible beauty that a sprung teak deck adds to any classic yacht.
Before installing the plywood subdeck, we added blocking to support the port and starboard panels where they would butt together at the deck centerline, as visible in photo 1. We also installed blocking in way of the foredeck hatch, chainplates, mast partners, and deck-mounted hardware.
In order to efficiently install the plywood to the deck structure, plywood panels were fi rst epoxied together to extend the full length of the boat’s deck from stem to stern, using 8:1 feathered scarf joints. We made one long panel for each side, to be butted at the centerline. Before the panels were permanently attached to the deckbeams, their undersides (seen in photo 2) were sealed with epoxy, primed, and painted, with the exception of areas to be glued down with epoxy.
We used epoxy to glue the subdeck panels to the deck blocking along the centerline and elsewhere. For the remainder of the subdeck, we used 3M 5200 adhesive sealant reinforced with No. 10 silicon-bronze screws driven into the deckbeams. The panels were initially cut a bit oversize so that after the adhesives cured they could be trimmed accurately to fit the hull.
The methods used in building the deck were repeated for the cockpit sole to make it equally strong and watertight. A unique aspect of the Dark Harbor 17 1⁄2’s sole, however, is that Crowninshield gave it a reverse camber in order to drain water toward the centerline and then forward. The ends of the cockpit sole’s deck-beams are approximately parallel with (but higher than) the waterline, but because their lengths increase going forward, their depths at the centerline increase, which creates a downward slope. Over its length of just over 7′, the sole slopes downward almost 2″, which causes any water to run forward to a drain just aft of the bulkhead, leading via a hose to a through-hull fitting below the waterline.
As soon as the 3⁄8″ plywood was installed over the cockpit-sole beams, cleats were installed along its perimeter edges to receive the footwell’s 3⁄8″-thick plywood sides and aft end; the forward end received a similar cleat for the 1⁄2″-thick plywood cabin bulkhead. Eventually, the cockpit sole, like the deck, was sheathed in teak planking set in epoxy, and all of the vertical surfaces were sheathed in a layer of 1⁄4″-thick Alaska yellow cedar staving glued to the plywood substrate.
Before we could turn our attention to the design and layout of the deck planks, we first had to decide on the construction method to use for the round-front cabin trunk and the cockpit coaming. The elliptical coaming in this boat is built as an extension of the similarly shaped trunk cabin, making the cabin and coaming a single assembly.
There are multiple ways to build this structure: One option would be to deck the boat first, then place the cabin and cockpit coaming assembly directly on top of the deck; however, it’s tough to maintain deck seams that disappear under other structures. Another way is to build a grub, or sill, to receive the cabin and coaming assembly. This is common on large boats, but it would add unnecessary weight to a small daysailer such as the Dark Harbor 17 1⁄2. Instead, we chose to install the cabin and coaming assembly over the plywood decking, then place our teak planking around the completed structure.
The cabin sides and coaming consist of pieces that needed to be steam-bent and scarfed together to form essentially one continuous oval of white oak that matched the deck opening and extended onto the afterdeck.
To ease access and clamping while bending the oak, we created a plywood pattern of the cabin and coaming footprint, showing the existing opening in the deck. This allowed us to take the work to the shop floor. For the best success with steam-bending, we used “green,” or unseasoned, white oak, so we wanted to get this part of the project underway as early as possible to give the oak plenty of time to cool, dry, and stabilize before its final installation.
Using the full-sized plywood pattern, we made a jig by installing brackets to support the oak during steam-bending. The bends at the forward and after ends are extreme, and they are a signature feature of the Dark Harbor 17 1⁄2s. Crowninshield drew plans for an alternative layout, with a straight athwartships section of coaming at the aft end of the cockpit instead of the distinctive oval, and this variation has been used in both original and modern Dark Harbor 17 1⁄2s. We, however, favored the beauty of the oval shape. The plans called for the cabin sides and coaming to be plumb, so the bending jig’s brackets could simply be made at 90-degree angles.
It is generally much easier to steam-bend wood around the outside of a curve than to the inside. Keeping this in mind, we planned the bends so that the placement of the brackets on the plywood footprint pattern matched the inside face of the cabin and coaming. By bending around the outside of the brackets, we were able to gradually increase the bend while fully supporting the freshly steamed oak with a generous number of clamps, with pads protecting the wood. By doing so, the oak had the best possible chance to bend without breaking.
The plans called for using two pieces of white oak, but our limited access to white oak in the Pacific Northwest forced us to use four pieces instead. To join the pieces, we used splined butt joints glued with G-flex epoxy. Each piece was initially milled to a thickness of 3⁄4″ and cut overly wide and long to allow for final fitting after the wood cooled. The students put two pieces at a time in the steambox for about 35 minutes, then bent them onto the jig in opposing pairs—starboard aft and port forward, then later starboard forward and port aft. We did this to allow plenty of room for the extra length to be supported by clamps. After all four pieces were successfully bent, the entire assembly was moved to a small loft space where it could cool and stabilize, with the brackets and clamps left in place, to prevent any deformation as it dried. Over the course of almost fi ve months, the oak shrank almost 3⁄4″ in width.
After seasoning, the oak pieces of the coaming and trunk cabin could be fitted to the deck. First, the two forward pieces were fitted together so that their splined and glued joint would correspond to the deck centerline. Then, the after two pieces were joined in the same manner. The remaining two butt joints awaited the final installation, and the top edges of all four pieces were left tall so that the final profiles could be cut after the oak was permanently glued and screw-fastened to the deck through the carlins and deckbeams.
One of the main challenges with any oval- or round-front cabin is making the deckbeams for its roof. The beams cannot be made to a single camber; instead, each one must be lofted individually to a camber that accommodates the rounded slope of the centerline of the cabintop, as shown in profile.
As we shaped and installed the cabintop beams, we temporarily sprung a centerline stringer to their undersides, as shown. This not only helped maintain the shapes of the beams while the first layer of the roof was being installed but also allowed for slight adjustments to create a smooth, fair surface. Where the beam ends met the cabinsides, half-dovetail joints locked the beams into a beam shelf that had been installed along the inside upper rim of the cabin sides.
Also note that in photo 9 the corner posts and bulkhead at the aft end of the cabin, as mentioned in photo 4, have been installed. We again chose a plywood substrate for strength and stability and later sheathed it with glued-in-place vertical staving.
After lightly fairing the cabin roof beams and routing a shallow channel in some of them to provide a wire chase for the overhead cabin light, we varnished the whole underlying structure, including the beams, the beam shelf, and the cabin sides, before planking the roof. Instead of using one layer of tongue-and-groove planking as with the original boats, we used two layers. The first, intended to preserve the aesthetics of traditional planking, consisted of 3⁄8″-thick tongue-and-groove Alaska yellow cedar glued in place with 3M 5200 and fastened with No. 8 silicon-bronze screws. After fairing, we installed a second layer, using epoxy to glue down 1⁄4″ marine plywood; this was later sheathed with 6-oz fiberglass cloth set in epoxy.
We made the plywood layer in two pieces butted together athwartships along one of the beams with the edged spiled to allow for the compound bend of the forward piece. The combination of planked and plywood-epoxy layers added considerable strength to the roof and made it watertight.
With the completion of the cabintop, the students were beginning to see the light at the end of the tunnel: the painted planking over varnished cabin structure, as shown in photo 10b, was their first glimpse at finish details of KOTIMANA’s interior.
Finishing the cabin and cockpit coaming gave the students fixed dimensions to work from while establishing the deck layout. As any boatbuilder will affirm, a good, clean-looking deck all comes down to planning the deck’s margin boards around the cabin and cockpit, kingplanks on the centerline, and covering boards along the sheer on each side.
Margin boards can be installed before or after the decking, but here at the NWSWB we encourage our builders to do the latter because the process makes the deck installation much easier. Deck planks can be installed a bit long for final trimming later, and by doing so you’re more likely to end up with fair and symmetrical margin boards and—especially—kingplanks.
This is a sprung deck, meaning that the planks parallel the sheerline as opposed to being parallel to the centerline. To build it, we first milled the teak planking stock to a thickness of 5⁄16″, which allowed for final sanding and fairing to a finished thickness of 1⁄4″. We settled on plank widths of 1 3⁄8″, after considering factors such as stability, availability of stock, and what width would spring to the shape without snapping.
Before doing anything else, we marked a fresh centerline on the 3⁄8″-thick plywood subdeck. Then we laid out the covering boards, using a width equal to twice that of the finished deck planks, or 2 3⁄4″, as shown in the accompanying drawing. Other considerations for deter-mining the width of the covering boards include the placement of stanchion bases, chainplates, toerails, and other fittings that may interfere with the covering-board seam. Making the covering boards wide enough to keep this seam accessible improves future access for maintenance and repair.
Our next task was to lay out kingplanks on the deck and also on the cockpit sole. Tapered kingplanks are common on most sprung decks. At our school, we typically taper them 1″ for every 10′ of length. In the end, trust your eye as to what looks best.
We try not to make the kingplanks too wide, since relatively narrow pieces of wood are more stable than wide ones. The width must also be proportional to the boat—the bigger the boat, the wider the kingplanks may be. For the Dark Harbor 17 1⁄2, we settled on a 5″ width at the cabin’s forward end, tapering forward to 4″ at the stem.
We used the same proportions for the after-deck, where the kingplank is much shorter. There, we started at the aft edge of the cockpit, planning the two pieces of the kingplank to taper toward the stern to give the elegant illusion that it was one piece, continuous under the cockpit coaming. Ultimately, these dimensions were used to mark kingplank reference lines offset to each side of the centerline, and we used these lines to plan the joints where the deck planks nibbed into the kingplanks.
Nibs are yet another important detail. The purpose of any nib is to eliminate delicate feather edges that would be hard to fasten and caulk and would likely split eventually. We try to scale our deck plank nib widths to between 5⁄8″ and 7⁄8″—again, all determined by the scale of the actual deck planks and relative proportions. For the Dark Harbor 17 1⁄2’s deck, a 3⁄4″ width seemed to be a good balance between.
After establishing the boundaries of the margin boards, covering boards, and kingplanks, we were finally ready to start installing the teak planking. Since we intended to lay the deck from the sheer inward, we glued down the covering boards first. This gave us a long, fair curve on each side to which we could spring the rest of decking.
As each strake crossed a kingplank reference line, we laid out a 3⁄4″ nib. First, starting from the point where the plank’s outer curve crossed the reference line, we drew a line 3⁄4″ long, perpendicular to the deck seam. From the inboard end of that new line, we marked another line extending to where the inboard edge of the strake crossed the margin reference line to complete the nib layout. This method worked for all the margins on the boat, whether forward or aft. After cutting just proud of the lines for later trimming, the plank was then ready for installation.
Nib layout is more complicated where the deck planks were to meet the curved margins at the coaming and cabin. Here, the angle between the decking and margins was in many cases so small that we simply created butt joints, as visible in photo 12. In cases where the angle was 45 degrees or more, we created nibs using the same method used for the kingplanks. One by one, the planks were dry-fitted. Because at this stage the margin boards themselves had not yet been installed, the deck planks could be left long and trimmed later.
Knowing the final thickness of the decking was just 1⁄4″, we chose to use temporary fastenings to hold them in place while the epoxy, which we used to glue them down, cured. Rather than risk damaging the fragile plank edges, and also to avoid obstructing access to the seams for cleaning out uncured epoxy, we chose to carefully drive temporary screws straight through the center of the planks that went through the subdeck and into the deckbeams. We waxed the screws for easy removal and used fender washers (as visible in the cockpit in the photo) to hold the planks down firmly. Later, we counterbored the resulting holes and bunged them.
When installing multiple deck planks simultaneously, we use 5⁄32″-thick spacers of ultra-high-molecular-weight (UHMW) plastic to assure that the seams are even. This material machines well, and epoxy doesn’t stick to it, making it ideal for this application. Before gluing, the teak planks were scrubbed with acetone to remove surface oils, thereby maximizing the epoxy bond between the teak and plywood subdeck.
We were also careful to remove any excess epoxy from the seams before it had a chance to cure. This is tedious work, no doubt, but it is much easier than removing hardened epoxy.
With all the deck planking installed, our next step before installing the margin boards and kingplanks was to trim the nibs to their final dimensions, using sharp chisels. This ensures that the nibs are symmetrical from port to starboard, and it also helps create good-looking seams—especially for the kingplanks. This step is critical. Once the seams are payed with caulking compound, any discrepancies in nib locations or seam widths become more pronounced.
After trimming and adjusting the nibs throughout the deck, we made 1⁄8″-thick plywood templates the margin boards. After the teak pieces were cut and dry-fitted, they were installed using the same methods as the deck planks. The kingplanks, in particular, were left a bit thicker than their adjacent planks to accommodate the deck’s camber during final fairing.
With all the teak deck planking adhered to the sub-deck and after a final fairing, the seams were ready for paying. We typically use Teak Decking Systems (TDS) caulking, which is a modified silicone that is very elastic and has tenacious bonding characteristics. When using this product, we don’t mask off the seams. TDS shrinks quite a bit while it cures, so instead we like to overfill the seams (using much more than you’d think!) to account for shrinkage. Excess TDS caulking can be trimmed with a sharp chisel once it cures, and then the entire deck can be sanded. The result is pure beauty and one of my favorite parts of boatbuilding.
KOTIMANA’s interior remained true to the original simple layout, with the exception of additional lockers aft near the bulkhead to house the controls, chargers, and other electrical components of the boat’s Torqeedo 4.0 electric sail drive propulsion system. The sail drive was installed off-center, with throttle controls leading to the cockpit.
Although it isn’t strictly necessary, the added propulsion will give KOTIMANA an often-needed boost in getting out of, or returning to, her marina slip in her new home in Auckland Harbor, New Zealand.
Long lengths of Sitka spruce—which Edensaw Woods in Port Townsend can often provide in 3″ thicknesses in lengths up to 40’—enabled us to use solid staves of spruce to make the spars, avoiding scarf joints. After setting up a long, perfectly fl at spar bench, the students began shaping all four spars at once—the mast, boom, gaff, and jib club.
The mainmast was constructed using a hollow box section that left room for wiring for the masthead lights. We installed a piece of plastic conduit to keep the void from filling with adhesive and later fished wires through it. After tapering individual mast staves and gluing the entire assembly together, the students shaped the square mast blank from four-sided to eight-sided, the stage shown in photo 16.
Next, they worked it to 16-sided and finally 32-sided before finally sanding the mast round. The boom, gaff, and jib club—which were all made of solid pieces—were shaped the same way. After sanding, the spars were sealed with a coat of varnish to keep them stable, and after the hardware was dry-fitted and final adjustments made, they each received 15 coats of varnish.
Port Townsend Foundry made custom bronze hardware and standing rigging for KOTIMANA. The beauty of this is not just in the bronze, but in the fact that all the hardware could be designed collaboratively. Hardware could be made specifically to the spars, and fittings could be created to help simplify handling or to reinforce strength where needed. The custom bronze spreader tips and brackets shown here are a great example.
The sails were made by Sean and Inger Rankins of Northwest Sails and Canvas in Port Hadlock. They also made all the custom leatherwork for the rigging, as shown in photo 17b.
After nearly 18 months of construction, with the participation of 16 students, the Dark Harbor 17 1⁄2 KOTIMANA was ready to launch (as seen in photo 18a) just before the 2018 Port Townsend Wooden Boat Festival, where she was exhibited. A couple of weeks later, after sea trials, the boat was packed into a 40′ climate-controlled shipping container, along with all of her equipment, destined for New Zealand. KOTIMANA now sails the waters of Auckland under the steady hands of her owner, and school alumnus, Kere Kemp (as seen in photo 18b).
Dark Harbor 17 1⁄2, is a 25′ 10″ LOA knockabout sloop designed by B.B. Crowninshield in 1908.
Sean Koomen is the chief instructor at the Northwest School of Wooden Boatbuilding. He can be reached at sean@nwswb.edu.