CNC Construction on the Rise

COURTESY CLC

The multiple bits on a modern computer numerical control (CNC) router can be changed automatically by the machine based on the task and material of the job at hand.

Back in 1996 I built my first boat (okay, my only boat), a slippery 14 (4.3m) skiff designed by multihull guru Nigel Irens. But while Irens had conceived the hull, it was his then collaborator—the young Ed Burnett who would go on to design his own line of modern classics before he died in 2015—who laboriously converted his lines into a set of drawings that could be cut by a computer numerical control (CNC) cutter. The result was seven sheets of plywood with dozens of sooty-edged components, which together with some hand-cut solid-timber parts and various bits of hardware, we marketed as the Western Skiff kit through Classic Boat magazine, which I was editor of at that time.

It was exciting to be building a new boat by one of the world’s top designers in a relatively new medium—CNC had been around for years but was only just spilling into the mainstream. We figured we might be on the cusp of something new in boatbuilding that would foster a resurgence in kit boats. What we didn’t anticipate was how keenly it would be taken up by professional boatbuilders, resulting in nothing less than a revolution in the industry.

CNC at CLC

COURTESY CLC

At Chesapeake Light Craft (CLC) in Annapolis, Maryland, CNC routers have been essential to cutting plywood boat kits for home construction since the 1990s. The AXYZ Automation Machine circa 1997 was rugged and reliable but had to be programmed in MS-DOS.

One of the first to see the potential of CNC cutting for amateur construction was John C. Harris of Maryland-based Chesapeake Light Craft (CLC). In 1993 he made his own kit cutter by bolting a Porter Cable router to the underside of a wooden table and using patterns to cut the parts out of okoume plywood. It worked reasonably well, even if one employee did lose a chunk of thumb to the router bit. Harris bought his first CNC cutter in 1997. It was a disaster, and after just a week he sent it back to the manufacturer. His second cutter came from Canada and ran “like a Swiss watch” for nine years.

Harris remembers some peculiarities of those early cutters, including router bits that had to be replaced daily, a vacuum table that needed plastic nails to make it effective, and an MS-DOS–based program that allowed titles of up to only eight characters, requiring “some linguistic inventiveness” to accommodate the several thousand distinct file names he required. It soon became clear to him that the CNC process was as much (or more) about the software as the hardware.

“Massaging CAD files for cutting on CNC machines was then, and is still, more art than science, much to the frustration of CAD/CAM engineers and salesmen who would like you to think otherwise,” Harris wrote in his blog. “While the popular notion of boat design in CAD is that everything is somehow automated, the reality is that nearly every inch of what you see here was teased into compliance by highly skilled humans.”

COURTESY CLC

CLC’s latest CNC machine, a 2014-vintage C.R. Onsrud, is capable of precision 3D machining.

He gives as an example the hundreds of uniformly spaced holes drilled into the mating edges of stitch-and-glue panels for each kit—a useful feature now automatically drilled by the cutter—but to get to that point each hole had to be manually drawn into the CAD files, adding hundreds of hours of extra work.

Harris upgraded his CNC cutter in 2006 and then again in 2009, this time for a machine with a tool changer that could automatically select different bits, and two tables, so one could be used for cutting while the other was being unloaded and prepared for the next operation. It also ran a different operating program, which required 3,000 existing files to be converted at a cost of around 10,000 man-hours, something Harris describes as about “as romantic as sticking a fork in your eye.”

COURTESY HEWES & CO

Hewes & Co. (Blue Hill, Maine) cuts small kit boats and large mold and bulkhead parts.

By 2014, it was time to upgrade again, this time to a Onsrud Pro Series costing $240,000, including software and other appendages (his original cutter had cost $32,000 in 1997). By now, the technology had moved beyond simply cutting planks and scarf joints to cutting intricately shaped parts “with tolerance measured in thousands of an inch, as well as hundreds of stitch holes, mortises, rabbets, bevels, and puzzle joints.” That level of finicky detail requires extra time, however, and Harris has had to institute shifts and overtime to keep the machine running 10 hours a day, sometimes six days a week, to keep up with demand.

“We’ve figured out clever CNC-cut joinery that spares the builders from needing skills with sharp edge-tools,” says Harris. “For example, when the Skerry design came out in 2002, the builders still had to use a rabbet plane to cut six gains in the upper strakes at the bow and stern—no different than the gains you’d have been cutting in a lapstrake boat in about 1950. It’s tricky, and looked bad if they fumbled it. These days, the CNC machine cuts the gains. Not only that, but we came up with clever interlocking geometry that’s quick to cut and looks great. The results are the overlapping strakes, which become planar in the last few inches. It’s perfect. That’s the result of a lot of CAD/CAM design struggle and evolution over decades.” (For more on CLC, see Steven Callahan’s profile of the company, “Easy Pieces” in Professional BoatBuilder No. 152, page 24.)

CNC Job Shop at Hewes & Company

COURTESY HEWES & CO

The router automatically nests mold parts to minimize plywood waste.

Another successful kit manufacturer on the U.S. East Coast is Gardner Pickering at Hewes & Co. (Blue Hill, Maine). Unlike Harris, Pickering doesn’t design the boats himself but cuts models provided by other designers, to whom he pays a royalty. His catalog of designers includes Iain Oughtred, François Vivier, Andrew Wolstenholme, and Doug Hylan. He suggests the sheer accuracy of CNC cutting sets a high bar for designers and kit makers alike.

“If you’re working from a blueprint, you have to spile the planks yourself, but there’s enough variation when you’re doing it by hand to make that work,” he says. “People who buy a CNC kit expect a higher level of perfection. They expect that plank to land to the millimeter where it says on the drawing. We usually have to make subtle changes to convert line drawings to be cut by CNC—slight changes to the planks, the molds, the stems, the transoms.”

Pickering gives an insight into the practical difficulties of CNC cutting when he describes how every sheet of plywood is a slightly different thickness and must be checked at each corner with a micrometer as soon as it arrives to ensure consistency. In the kit-building world, a sheet of 18mm ply that is actually 18.1mm (0.7126) or 17.9mm (0.7047) thick can make a huge difference to a scarf joint. Similarly, different countries have different size sheets of ply: Bruynzeel is 2.5m (8.2 ) long, whereas meranti is 2 (51mm) shorter than that because it’s imperial, whereas Australian ply is 2.4m (7.87 ) long. It’s enough to stop you sleeping at night.

Vivier: CNC Kits in France

COURTESY FRANÇOIS VIVIER

François Vivier specializes in CNC-cut kits for traditionally styled boats like this 14’6″ (4.4m) Ilur.

Meanwhile, on the other side of the Atlantic in France, naval architect François Vivier has been spearheading the CNC revolution with his own range of small-boat designs. When he first started designing small traditional vessels back in the early 1980s, Vivier was still working in the research and development department of France’s largest shipyard, Chantier de l’Atlantique (St. Nazaire).

“CNC cutting had been used for a very long time to build tankers and passenger ships, so I was completely familiar with the principle,” he says. “CNC cutting for a small dinghy is very similar to cutting for a big vessel—you just cut plywood instead of steel.”

Vivier produced his first CAD design in 1997. The project was for a traditional working boat from the Île-Tudy, on the west coast of France, which was to be built by the local community as part of the Bateaux des Côtes project masterminded by the French magazine Chasse Marée. To simplify the process for the mostly amateur construction team, Vivier produced full-size frame templates printed on Mylar by a local print company, necessitating his first set of CAD drawings. It was a turning point, and ever since all his designs have been produced in CAD.

Soon after, Vivier teamed up with aspiring boatbuilder Pierre-Yves de la Riviere. The pair’s first collaboration was the prototype of the 22 (6.7m) Stir Ven, an early “raid” design with a heavy steel centerboard and big rig, which de la Riviere built for himself in 1998. The second Stir Ven was built for Vivier and was CNC-cut (the first Vivier boat to be produced this way), although it was essentially a traditional construction.

COURTESY FRANÇOIS VIVIER

CNC-cut plywood panels for a Méaban model are inventoried at builder Grand Largue, in France.

His real marriage of CNC and CAD took place in 2003 with the introduction of the Minahouet design, which took the concept a stage further by integrating an “eggcrate” construction, whereby the internal structure of the boat, including bulkheads, frames, and most internal furniture, slot together to form a grid on which the planking is laid, minimizing the need for temporary molds. The process offers huge savings in time and materials, which appeals to amateurs and professional builders, too. Under the brand name Grand Largue, de la Riviere is now the biggest builder of Vivier boats in France.

It’s a constantly evolving process. Vivier recently digitized his plans for the 146 (14.4m) Ilur—designed in 1985 and still his most popular model—and optimized them for CNC production. That included replacing the laminated frames with plywood bulkheads and the timber keel and stem with sandwiched plywood parts. The result, according to de la Riviere, was a 20% reduction in build time.

COURTESY FRANÇOIS VIVIER

The stiff “eggcrate” construction of CNC-cut interlocking transverse and longitudinal frames and bulkheads is visible in this Méaban built by Thierry Fouchier.

“We are using more and more plywood parts,” Vivier says. “If you can build the stem by gluing three layers of ply, instead of making a mold, laminating the wood, and cutting the bevels, that’s a huge savings in time. This is especially useful in France, where good boatbuilding timber is very hard to find. If we want good timber, we usually have to use Douglas-fir imported from the U.S.”

While it’s a technological advance, there’s a degree to which committing a design to CNC technology seems to freeze a design in time. For instance, Vivier’s Stir Ven and Minahouet designs were drawn using a software that is now outdated, so the only way to alter those designs would be to completely redraw them in Rhino, the program Vivier now uses.

Altering details of the carefully thought-through complexity of an interlocking eggcrate grid structure can be a major headache. It took Vivier nearly four days just to enlarge the cockpit of his Pen-Hir model for an American client. He’s understandably reluctant to revisit other designs.

CNC for Production Builders

The technology has its downsides, as de la Riviere has discovered. Often the skilled craftsmen he recruits to work at Grand Largue find the repetitive nature of the work boring and leave after building just two or three boats. “Most of the time they are making epoxy fillets or sanding and painting, which is not very interesting,” says Vivier. “There are very few tasks which are true carpentry work.”

It’s a problem other yards have tried to tackle by deliberately leaving some interesting woodwork for the shipwrights to practice their trade, even though it might be more efficient to CNC cut.

Production FRP boatbuilders, such as Hinckley Yachts in the U.S. and Bénéteau in France, were early adopters of CNC cutters for plywood components that could be quickly assembled to produce the internal joinery. What’s more, they could afford to invest in the expensive machinery to make it all happen. The process also proved surprisingly well-suited for building semi-production wooden boats, even supplanting the use of fiberglass in some cases.

Swallow Yachts in Wales had been building a successful line of small fiberglass boats for years, ranging from the BayRaider 20 expedition boat to the BayCruiser 23 pocket cruiser. In 2018 owner/designer Matt Newland pushed the design envelope with the Coast 250, a micro-cruiser that could plane under power and yet still performed well under sail. It seems the world wasn’t ready for such a revolutionary concept, however, and the boat flopped without even recouping its tooling costs. It has now been relaunched as the BayCruiser 26 (25 9/ 7.84m) with more traditional styling and may yet make a profit.

When it came to launching his next design, Newland was leery of going straight into GRP production with all the associated tooling costs. The Whisper 300 was the first motorboat built by Swallow Yachts and already carried an element of risk. But the yard had built several boats in wood—mainly the BayRaider 20, sold at a premium in plywood-epoxy and which Newland was interested to discover came out 20% lighter than its resin-and-glass counterparts. With increasing market awareness of environmental impacts, it seemed the right time to make the switch. A plywood-epoxy boat would not only have better end-of-life disposability, but it would also be lighter and therefore require a smaller engine, less fuel, and a smaller fuel tank, making it even lighter: in short, a virtuous circle of efficiency.

Newland was persuaded to build the new boat in plywood-epoxy. It helped that, thanks in part to a grant secured from the E.U. before Brexit, the yard had acquired its own CNC router to cut parts for the GRP boats. Building a CNC-cut-plywood boat would help amortize that investment. Newland was already familiar with the software, having spent the past two decades drawing boats in CAD (including a stint with superyacht designer Tony Castro), but building a semi-production boat from CNC parts required a different mindset to building one-off prototypes, where some degree of inefficiency was to be expected. It was a challenge Newland, a degreed engineer, took up with enthusiasm.

“To build efficiently in wood you need to think how the guys are going to sand that surface and finish it, because that’s where all the cost is with wood,” he says. “You try to keep things plain and simple over a lot of the surfaces. It’s always about the worker with a sander who’s got to finish every single fillet and every single piece of wood.

Nic Compton | Professional BoatBuilder Magazine

The Whisper 300 model was the first powerboat from Swallow Yachts in Wales. The goal was to simplify the build by CNC-cutting every piece of wood in the 30.6′ (9.32m) plywood-epoxy semi-production cruiser.

“The point of the Whisper was to CNC-cut every single bit of wood that went into it. The aim was to take a part off the CNC machine, maybe give it a little tickle with sandpaper to clear off any burrs, but then [it] can be fitted where it’s supposed to go, with no need for a drill, saw, chisel, or anything. It just fits—whether it’s the backrest, the seat top, the bulkhead side—whatever it is, it should fit together with no need to tweak anything. We didn’t get there with boat No. 1, but we are getting there now.”

With four boats built to the design, the cutting list has been streamlined so there are only six items cut from solid timber, including the gunwales and inwales, each nearly 30 (9.1m) long, and some shelving battens, which are easier to cut on the bench saw.

The savings for commercial builders aren’t just in time but in materials, too: The more parts you can squeeze onto each sheet of ply, the greater the savings, and the tighter the glue joints, the less epoxy you’ll need. Spirit Yachts (U.K.) reckons it has reduced wood waste by 20% by switching to CNC, with resulting benefits to the environment. Nigel Irens, who has invested heavily to optimize his latest powerboat, the 26 (7.9m) Clara (see PBB No. 200, page 8), for CAD-CNC construction, was surprised at how much epoxy he saved, thanks to improved accuracy throughout the build.

The Whisper experiment has clearly been a success, and even though Newland has had to up the price from £128,000 to £169,000 (ex VAT) ($156,160 to $206,180 U.S.) to make a profit, he now has a backlog of orders. He’s already contemplating a bigger sailboat design, the BayCruiser 32, which will be built in wood, though significantly he still intends to build the newly launched BayCruiser 21 in fiberglass. From hard-won experience, he reckons production plywood-epoxy construction is economical only for boats longer than about 30 (9.14m).

“I’m really excited and energized by the potential for this method of construction,” he says. “It’s obviously not traditional boat construction. It’s not knee-deep in cedar shavings and get your adze out, but the trouble with that sort of construction is who’s going to pay for it? I think the potential of this method is really quite big.”

Large Custom Builds

COURTESY BROOKLIN BOAT YARD

A combination of CNC-cut temporary molds and permanent bulkheads on this semi-custom Wheeler 55 powerboat eliminates the time, space, and workforce demands of traditional lofting for such a large vessel.

The CNC revolution hasn’t just transformed the work practices of kit manufacturers and production boat builders; it’s also very much a factor in another booming market segment: big custom-built wooden sailboats. Maine yards such as Brooklin Boat Yard (BBY), Rockport Marine, and Artisan Boatworks are all seemingly swamped with work, building bigger and bigger boats—95 long in the case of the latest project at Rockport Marine. All three yards extensively employ CNC-cut parts.

“We started using CNC 10 years ago to cut temporary hull molds and bulkheads,” says Will Sturdy, designer at BBY. “Now we cut as much as possible on CNC to save time.”

Sturdy estimates that using CNC-cut parts saves around 10%–15% in hull construction time. This doesn’t come free of course. It requires a lot more detailed work in CAD to achieve the necessary level of detail. But Sturdy reckons for every 40 hours at the computer, the yard saves 400 hours on the shop floor. And he points out that most of the work the CNC cutter has taken over is low-skilled chores such as “chasing a line with a jigsaw,” which no one misses.

One of the first applications of CNC cutting at the yard was in 2015 on the 74 (22.6m) sloop Foggy, designed by German Frers with styling by the celebrity postmodernist architect Frank Gehry. With multiple layers of materials in the hull—plywood, carbon fiber, foam, larch, and red cedar—not to mention 500 glass portlights inlaid in patterns into the hull and deck, it’s hard to imagine how the boat could have been built without extensive use of CAD design and CNC cutting.

But CNC has its limitations on bigger projects, such as laying a deck. Although BBY does sometimes use CAD to plot the layout of plywood deck panels and cut them in CNC, often it’s quicker and more accurate to do it by hand.

COURTESY BROOKLIN BOAT YARD

CNC-cut molds also simplify construction and ensure accuracy in the shape of the Wheeler’s radiused transom.

“With CNC, you get locked into the precision of the whole process,” Sturdy says. “Every step has some tolerance—sometimes it’s 0.05mm, sometimes it’s 0.5mm—but add all those up, and with our standards of joinery, if you’re seeing a visible glue joint, that’s too much. You can’t hit that level of precision on multiple pieces without some degree of hand-fitting at the end. At some point it’s just simpler to put the sheets on the boat and cut the edges to fit than it is to map everything out.”

Unexpectedly, perhaps, heeding the practice of Pierre-Yves de la Riviere in France, Sturdy says some of the detailed tasks, such as complex interior moldings, which could be CNC-cut, are deliberately left to be cut by hand at BBY so shipwrights can practice their skills and maintain the yard’s reputation for bespoke craftsmanship—and also, perhaps, to hang on to its skilled workforce.

Although perhaps best known for the range of kit boats he cuts at Hewes & Co., Pickering says his bread and butter is supplying CNC-cut parts to commercial boatyards in his corner of New England. He has seen that work increase massively in recent years, from simply providing hull molds and bulkheads to, in some cases, supplying whole interiors.

“Sometimes I cut more sheets for Brooklin Boat Yard in a week than I cut kits in a year,” he says. At that volume, why don’t all his customers simply install their own CNC cutters? Pickering is quick to point out that his best customer still uses, at most, only 10% of his cutter’s capacity, meaning that if the yard bought its own cutter, it would sit idle 90% of the time. Then management would have to start thinking of ways of keeping the machine busy, rather than focusing on what it’s best at: building boats. Even Swallow Yachts, which is geared toward CNC boatbuilding, manages to keep its cutter running only 50% of the time.

COURTESY BROOKLIN BOAT YARD

When it comes to sheathing the bottom of a boat the size of the Wheeler, it’s easier to fit sheets of plywood to the frames and trim the edges than to have all those panels CNC-cut and fit to perfection from design files.

The work comes to Pickering in different stages of progress: from 3D models of deck structures, which he has to “squish” (an actual command in Rhino) into 2D and arrange onto sheets of ply, complete with puzzle joints; to cut-ready files where all the parts are nested into separate sheets and he simply has to “mow the lawn” and check that everything fits. “The real advantage with CNC-cut molds is that if it’s done right, there’s no fairing needed,” he says. “It all just fits together.”

Pickering’s work isn’t confined to plywood. He also worked with R&R Duffy LLC to supply the molds for its 35 (10.7m) fishing boat, which Richard Duffy and Spencer Lincoln came out of retirement to build in 2021. Pickering’s main problem is finding skilled operators to run his CNC cutters; he says he’d buy another machine tomorrow if he could find someone to run it. On the other hand, Matt Newland at Swallow Yachts reckons it takes only a day to teach someone to use the cutter, plus another three to four days to teach them the relevant parts of the Rhino CAD program.

Conclusion

Things have certainly come a long way since we launched the Western Skiff kit back in 1996. Far from consigning wooden boats to history, CNC cutting has helped generate a surprising revival. Combined with CAD design, it has evolved into an efficient and economical method of building custom and even semi-production boats at a professional level. For many, it is quite simply a marriage made in heaven.

Irens: “I had a moment of realization that in terms of reducing build time and creating absolute reproductivity, we were only looking at the tip of the iceberg. People like Paul Smith [his local CAD programmer and CNC cutter] could take this whole thing another huge step forward. It made me realize what opportunities might be opening up and that I had to get in that mindset again, because these are quantum leaps forward.”

About the Author: Nic Compton is a freelance writer/photographer based in Devon, U.K. He lived on boats in the Mediterranean until the age of 15 and worked as a boatbuilder for many years before swapping his chisel for a pen and his router for a computer. He sails a Rhode Island–built Freedom 33, currently based in Greece.