Chris Cameron PhotographyKOTIMANA, a Dark Harbor 17 1⁄2, was built at the Northwest School of Wooden Boatbuilding in Port Hadlock, Washington, for New Zealand sailor Kere Kemp, who studied boatbuilding at the school.
“Her lines sang to me,” Kere Kemp says of his dream to one day own a Dark Harbor 17 1⁄2, the iconic daysailer designed by American naval architect B.B. Crowninshield in 1908. “I loved the classic, old-school lines, the full keel, the hard turn of the bilge, the gaff rig…. She’s a relatively small boat but a true classic.”
Kemp is not alone in admiring those lines. Members of the current fleet can be found stretching their sails and turning heads not only on both coasts of the United States but also from Europe to the South Pacific. This article describes how we built Kemp’s Dark Harbor 17 1⁄2, KOTIMANA, with a crew of 16 students at the Northwest School of Wooden Boatbuilding in Port Hadlock, Washington, where I am the lead instructor. Kemp knew the school well, having studied traditional wooden boat building with us and graduating with the class of 2016. “I knew the quality of the build would be superb,” Kemp says, “and that the design, lofting, and build would be a genuine challenge and a genuine hit with the students during the two years it would take to build.”
Starting with lofting in January 2017, I led the first phase of construction with a crew of 10 students (six others joined later). Each had absorbed the lessons of an intense three-month introductory course called Beginning Projects. This included a month of joinery and hand-tool practice, a month of drafting and lofting, and three weeks building a flat-bottomed skiff. Their transition from the “flattie” to the complex shapes of the Dark Harbor was a challenge—and my challenge was to keep all the students busy on a 25′ boatbuilding project.
In the first week alone, we lofted the hull lines, built the strongback, laminated deckbeams, and shaped the transom. In other words, from Day 1 the project launched off in every direction.
We built the hull and deck simultaneously, on two separate jigs. We derived mold shapes for both jigs from the lofting.
The molds for the hull were set up for upside-down construction, as shown in photo 1, which simplifies the work of planking. We built the molds of 3⁄4″-thick pine, with edges beveled to the hull shape. Molds forward of amidships were installed with their aft faces lining up with their corresponding station lines; for those aft of amidships, the forward faces lined up with the station lines.
A second set of molds, consisting of partial molds referenced to the load waterline, were set right-side up on the floor to provide the best access for building the deck structure after we moved the lofting board out of the way, as shown in photo 1A. These molds were straight-sided, since the only part of the molds receiving hull parts touched on the sheer clamp and the beam shelves. We cut them to receive the steam-bent sheer clamps at angles derived from the lofting. We also cut a notch in each mold to index the beam shelf.
The mold-making process gave the students loads of experience translating the lofting from two dimensions into three and helped set the project’s fast and efficient pace. It also helped the students develop an eye for accuracy and detail, laying the foundation for craftsmanship.
This approach was evident even in the simplest of details. We sprung the sides of the strongback for the hull, for example, to match the plan-view curvature of the hull, and we set them 6″ inboard from the sides to minimize obstructions during construction, as visible in photo 1.
As one pair of students fine-tuned the strongback, another pair lofted the hull lines. We used the lofting to make construction molds for the hull, using Mylar sheets to transfer the shapes to the mold stock, as shown. (For more on lofting, see WoodenBoat Nos. 110–111 and my article on lofting transoms in WoodenBoat No. 257.) As each mold was completed, it was installed in its correct alignment on the strongback.
The Mylar sheet, which is traced from the lofting, is draped over the piece so that the lines can be directly transferred to the mold stock, using push-pins as shown. (For more on this, see “The Prothero Method” in WoodenBoat No. 249.) For the greatest accuracy, we transfer all the lines needed to make the molds onto a single Mylar sheet to ensure that they all reference the same centerline and waterlines.
Meanwhile, other students made patterns and pieces for the keel—which are shown here—as well as those for the stem and transom. As these were completed, they were installed over the molds and fastened with silicon-bronze bolts. The sprung plank keel for the Dark Harbor was shaped out of Honduras mahogany. In the original construction, the garboard planks fitted directly to the keel timber.
At the recommendation of other Dark Harbor builders, we chose to add a keel apron, or inner keel, also of mahogany. This helped beef up the backbone assembly and increase support for the garboards’ inboard edges and fastenings. The two pieces were bedded together, sprung over the molds, and eventually through-bolted to the floor timbers. Ultimately, this structure also improved support for the fin keel and ballast.
In this photo, the students are marking mold locations onto the keel apron. (The keel timber is visible to the left of it.) These locations were derived by springing a batten into place over the molds at the centerline then marking the mold locations directly to the batten. Then, laying the batten flat on the keel apron stock (and earlier for the keel) gives the true, “expanded,” station spacing along the length of the pieces. (The other long pieces shown at the left are the rough stock for the sheer clamps.)
Planning ahead to simplify the installation of Honduras mahogany floor timbers and white oak frames, the students used stepped molds, which are uncommon.
Typically, boatbuilders in the Pacific Northwest make molds by beginning with a sectional shape from the lofted lines plan, which is to the outside of the hull, and then deducting from this shape the thickness of the planking, the thickness of the frames, and the thickness of longitudinal ribbands over which the frames are steam-bent. The deductions assure that the outside of the finished hull will exactly match the designer’s lines.
Our stepped molds deducted for those thicknesses (including the ribbands) everywhere except in way of the floor timbers, where we deducted only the thickness of the planking. This makes a transition—a “step”—in the curve of each mold’s outside edge. The steps on each side of each mold correspond with the outer ends of its corresponding floor timber, as determined from lofted construction details. Floor timbers are notoriously complex to make, so the stepped molds allowed much better access, making very straightforward work of patterning, shaping, and installing each of the boat’s floor timbers—32 of them in the case of the Dark Harbor 17 1⁄2.
After the molds had been erected and the keel assembly sprung into place, we added three Douglas-fir ribbands on each side between the keel and the outer ends of the floor timbers, as shown by the steps in the molds. Because the mold locations were chosen to stay clear of floor timbers and frames, we had room to later through-bolt the frame heels to the floors while access was easy.
The bevel for the top edge of each floor timber was picked up from the lofting, as was the bevel for the edge mating to the keel. Patterns for the “wings” of the floor timbers were taken directly from the keel and ribbands. Pattern stock was temporarily secured to the keel using small wooden brackets. With the patterns set plumb, all bevels for the floor timbers could then be measured using a bevel gauge.
Access was such that a half dozen students could pattern and shape the Honduras mahogany floor timbers simultaneously. A final detail was to cut limber holes in the floor timbers before their final installation. Here, the temporary fastenings through the keel into the floors are visible; they were later replaced with silicon-bronze bolts through the keel, apron, and floor timbers.
As half the students worked to pattern and install the floor timbers, another crew built the molds and set up the jig for the construction of the deck. Given that each of these molds would only have to support the deck from the sheer clamp up, their lower edges were cut to match the load waterline, making them much simpler and faster to build than the hull molds. The load waterline was chosen as the cutoff point so that the deck structure could be built at a convenient working height. The heavy pieces inside the building jig are stringers fastened to the cross spalls to stiffen the jig and keep it in proper alignment.
With the deck molds completed, a team got to work patterning and shaping the western larch sheer clamps and beam shelves, measuring directly from the deck molds. Larch bends beautifully, making it an ideal wood for this purpose. The sheer clamps were installed first, and temporary plywood braces at each mold, visible in the photo, added support, especially aft, where the twist was severe. These braces cleared the way for spiling the beam shelves, which were through-bolted vertically to the sheer clamps.
Crowninshield’s original design called for a single on-edge sheer clamp per side. We added to this a horizontal beam shelf above the sheer clamp (see “The Prothero Method,” WB No. 249). This not only added structural stiffness to the deck but also allowed for more efficient installation of the deckbeams, as shown below. Considering that the deck would eventually have to be joined with the hull, a false stem and a false transom matching the dimensions of the actual ones were included to give accurate measurements for bevels and length. As the sheer clamps and beam shelves were fitted to the false stem and transom, the deck and hull reached simultaneous milestones: the deck was ready for deckbeams and the hull was ready for frames.
With all the floor timbers installed and final adjustments made to the hull setup, the remaining ribbands—plus one heavy western larch bilge stringer per side, visible here at the turn of the bilge—were installed. The position of the bilge stringers, which are permanent, was determined from the lofting. Also, note that the final silicon-bronze bolts for the keel, apron, and floor timbers have been installed here.
After fine-tuning the backbone assembly, the students next installed the frames. Over the course of two-and-a-half hours, 10 students steam-bent and installed more than 70 white oak frames. Their method was efficient: the 7⁄8″ × 7⁄8″ frames were bent in pairs—one on each side, to be installed simultaneously. The frame heels were first inserted under the three ribbands used to pattern the floor timbers, as visible in the photo to the left, then bent over the rest of the ribbands.
The frames were initially clamped in place; after they cooled, the clamps were removed and replaced with plastic zip ties. We had some frame breakage, especially in the tight radius of the hull’s turn of the bilge aft. But the students persevered, the broken frames were discarded and replaced, and the entire job went beautifully. One final detail was to cut the frame heels 3⁄4″ short of the keel apron to create limbers for water drainage.
After framing, the students lined off the hull for the 3⁄4″-thick western red cedar planking. Planking the hull upside down is much easier than right-side up, and eight students began to spile and shape their planks simultaneously, two from the garboard up after removing the three innermost ribbands on each side, and two from the sheer down, on both sides.
We used wedges set against blocks clamped to the frames to edge-set the planks tightly together. Two curved bar clamps, visible here, were used where we had access to to get the plank fits tight. These are common pipe clamps, but we “recurve” them each time to shapes that match the hull.
The plank fastenings were 1″ × No. 10 silicon-bronze screws, counterbored and bunged.
With the planking well underway, the deck crew began laying out and installing Honduras mahogany deckbeams. These had been laminated over “traps,” or bending jigs, and varnished before installation. The deckbeams were bolted to the beam shelves using 1⁄4″ silicon-bronze carriage bolts. In way of the partial spur beams, temporarily sprung stringers held them in alignment with the deck camber until they were fastened to the beam shelves; permanent carlins were installed later.
The entire assembly was sanded and varnished in preparation for meeting the hull. At the same time, the nearly planked hull was also faired and primed in preparation for its rollover.
Lachlan Carlson, who came to the school right out of high school, drove the final sheerstrake fastening, completing the unification of the hull and deck structure. The sheerstrakes and first upper strakes had been left off, to be hung only after the frames were bolted to the sheer clamps.
A fast learner, Carlson had also worked on some of the most complex pieces of the Dark Harbor 17 1⁄2, including the stem and the curved, raked transom (see WoodenBoat No. 257) and served with a crew from the Northwest School of Wooden Boatbuilding that completed a Haven 12 1⁄2 at the Wooden Boat Centre in Franklin, Tasmania, ahead of the Australian Wooden Boat Festival in Hobart (see WoodenBoat No. 268). He has since gone on to join the crew restoring the John Steinbeck–associated fish boat WESTERN FLYER at the Port Townsend Shipwrights Co-op (see WoodenBoat No. 267).
We intentionally kept the deck-beams from touching the frame heads—something we had decided while lofting. One of the main advantages of using the combination of sheer clamp and beam shelf is that no fastening is needed through the frame head and deck-beam ends, as is common in other types of construction. If a fastening were added there, either the frame or the deck-beam or both would likely crack over time, since the scantlings are so small on a boat such as this one and the end grain is so close.
It would be a vulnerable connection from Day One. With the deck structure in place after five months of work, 10 students who had had little or no previous boatbuilding experience had built both a new hull and a new deck, separately, and then united them.
Sean Koomen is the chief instructor at the Northwest School of Wooden Boatbuilding. He can be reached at sean@nwswb.edu.
In Part 2 of this series, we’ll focus on laying out and installing the teak deck, steam-bending the cabin and cockpit sides, shaping spars, installing hardware, and sailing the boat.