Van der Werff’s Curved Wood

van der WerffImka Westerhuis

Business partners Roelof van der Werff (left, with cap) and Henk Bergsma (center) help carr a preshaped hull panel into the ancient boatbuilding shed at Scheepstimmerwerf De Hoop in Workum, Netherlands.

We choose to be pioneers of new sustainable yacht construction,” Roelof van der Werff says. “We use bamboo and radiata pine wood. We have hull sections of this wood bent into three-dimensional shapes. With this procedure, we create panels that together form a hull. Yacht builders should start using the renewable materials that grow all around us.”

Inside a 1780-vintage boatbuilding shed, surrounded by Dutch shipbuilding history, Van der Werff is returning to a material that once dominated the industry. He’s building a line of motor launches and a sailing catamaran from wood. His shop in the Scheepstimmerwerf De Hoop in Workum employs modern technology to bend the wood into curved panels for his modern yacht designs.

Van der Werff comes from a long shipbuilding lineage. His grandfather was one of the regional legends building sailing barges called Tjalken in the northern Dutch province of Friesland. “Wooden boat building as state-of-the-art craftmanship has vanished with my grandfather retiring,” the grandson reflects. “It remains as heritage for those [clients] who appreciate wooden boats so much that they are willing to pay for all the craftmanship and upkeep—the extra maintenance a wooden boat usually requires.” But Van der Werff also sees a practical future. “Innovation in wooden boatbuilding is needed. The marine industry is using materials that cause a lot of pollution during production, and in the case of composite boats, these materials can often not be recycled and end up as landfill,” he says. “We aim to develop ways of production with renewable materials that change yachting towards sustainability.”

Van der Werff’s Bamboo Cat

In their yard next to a shipbuilding museum, Van der Werff and his partner, Henk Bergsma, build wooden motor launches called Werffboats and a design called the Bamboo Ark. It’s a sailing catamaran whose identical hulls—connected with detachable beams—when taken apart can be used as canoes for access to shallow waters.

During my visit they were working on the first 12m-long (39 ) catamaran for Geoversity, an environmental protection project based in Panama. Committed to biocultural renewal, the organization found Van der Werff and Bergsma while researching sustainable yacht construction methods. Its intention is to use the catamaran (or single hulls) to explore the waters running through its campus in the Mamoni Valley Preserve.

The hull structure is made with preshaped bamboo composite panels that the builders also want to introduce as a yacht-building material. In the old shed I found a set of wood molds for assembling the preshaped 3D hull sections. “This is the second time in wooden boat building history that pre-formed sections of the hull will be produced elsewhere than on the frames,” Van der Werff says. “The first time was when we built Petronella, our demonstrator motoryacht. It will also be the second time these preshaped sections will be from wood formed into compound curves. Where Petronella was constructed with Accoya wood strips, the catamaran will be built from bamboo strips.”

van de WerffImka Westerhuis

The conventionally assembled deadwood and molds for one hull of the 12m-long (39′) Bamboo Ark catamaran stand between Bergsma and Van der Werff.

van der Werff fitting a panbelImka Westerhuis

Molded-wood hull panels of the 24′ (7.3m) motor launch Petronella are placed on the mold and transverse frames.

The Cure for Curves

The experiment of creating a boat hull with preshaped panels of 3D- curved wood started with Van der Werff reading an article about the two-way bending methods of the specialized Dutch composites molding company Curve Works. He asked if the company would like to use its adjustable molding table to create curved, domed wood panels for boatbuilders. The answer was yes.

The technology developed by Curve Works enables forming curves, blisters, and other wavelike shapes in composites, plastics, and wood to exact dimensions. The tailored shapes are formed from panels laid out and cured on a malleable table surface supported by multiple actuators that extend or retract to form the desired shape. A designer’s digital drawings specifying the set curvature of each part of a structure are loaded into the Curve Works table software, which uses the information to control the table’s vertical rods (actuators) to create a mold surface of the designed shape.

“We have patented our method of curving wood,” says Curve Works founder and chief technology officer François Geuskens. “We use our adaptable mold to define the exact shape as designed by an architect, furniture builder, or in this case, a yacht builder. We do not use ready-made plywood, because that would break, especially if we were to bend it in two directions. We have wood veneer that we lay over the table—or adaptable mold as we prefer to call it. [Several] layers of veneer are glued together. We use glue that has sufficient pot life to be brushed over the consecutive layers so we can assemble all of the veneers to the required thickness.”

Loading is done while the mold is relatively flat. He explains, “The newly created plywood is vacuum-bagged over the mold. When all the veneer and glue is stacked, the adaptable mold changes shape into the curvature as set by the digital design. The glue, still runny, acts as a lube between the sheets of veneer that will slide along each other to form the curved shape. When the glue has reached its curing time, the plywood will be curved as the mold is. After removing the vacuum bag, it keeps the exact shape.”

Full-width sheets of veneer can accommodate only moderate two-directional curves. “A sheet of veneer is much like a sheet of paper,” Geuskens explains. “You can’t bend a sheet of paper around a ball. If you want a smooth curving form in two directions, it needs to be cut. Creating more extreme forms, we build plywood using strips of veneer.”

The product of this Curve Works–patented procedure is identified as Curved Plywood.

van der WerffHans Buitelaar

At Curve Works, Van der Werff and company technicians stand by as strips of Accoya-brand acetylated pine (treated for durability) and epoxy resin are vacuum-bagged on the adjustable mold.

Strips and Rhombus Shapes

To achieve the strength required for a yacht hull, the preshaped panels are a composite of layers of wood or bamboo with fibers and resin. Bamboo comes in long, thin strips glued to a thin scrim of flax fibers. In construction, the laminates of bamboo backed with scrim are laid over the shaping table and then cured with resin. In the early experimental stage, this was done by hand layup and resin application, but with placement and resin ratios worked out, most hull panels are now vacuum-infused. There are some exceptions with certain wood types and when the weight of a panel is critical. Then curing is done without vacuum-bagging to avoid the side effect of weight gain as excessive resin is driven into the wood by the infusion pressure.

Besides bamboo, the boatbuilders have primarily used Accoya. This is a cured pine, acetylated for durability. Supplier Accsys Technologies promises 50 years of maintenance-free use of Accoya above the waterline and 25 years below it. The durability treatment for pine was developed for land-based construction and has been used for jetties in marinas. Pine trees have many desirable qualities. With slight variations they grow in many climates, grow relatively quickly, and can be sustainably harvested.

van der WerffHans Buitelaar

The partners have built two different panel types on the adjustable mold to date: veneered and varnished Accoya, and unfinished bamboo.

Prior to his partnership with Curve Works, Van der Werff built his Werffboat 21 using Accoya in traditional plank-on-frame construction. For the molded panels of the Werffboat 24, the treated pine, like the bamboo, can be cut into long strips that will easily bend to the shapes defined by the Curve Works computer-controlled table. Using three layers of 3mm-thick (0.12) Accoya strips bonded with intermediate fiber scrim and bio-based resin will yield a 1cm-thick (0.39) hull skin. Where compound curves are particularly challenging, the builders aren’t limited to applying long strips. Rhombus-shaped panels of thicker wood can be glued to a scrim of glass fiber or other material, stacked in staggered multiple layers, and then cured on the vacuum-infusion table. Working with builders like Greenboats in Germany, Werffboat also looks for bio-based epoxy resins and natural fiber cloth, like flax.

“The glass fiber scrim is not structurally needed,” Geuskens says. “Having the rhombus shapes or even the long strips of wood pre-assembled on a fiber scrim will help to work fast.” Speed is particularly important in this application, because the adaptable mold is an expensive piece of equipment, and clients pay by the hour to use it. Individually placing all the small rhombus-shaped pieces of wood on the mold would take too long, but when the materials for the 3D-curved hull panels are pre-assembled at the workshop, time loading the mold is minimized. Remember that the method of loading the mold and then applying the shape to the laminate requires epoxy with a long open time, and the newly formed plywood structure will need to stay in the mold much longer than that to fully cure.

Van der Werff says the fully cured curved-panel’s strength results from the wood strips and glue bonding. He insistst that the scrim does not add strength to the final structure.

van der WerffImka Westerhuis

The Curve Works adjustable mold is a grid of vertical actuators tied to a computer controller that adjusts the shape of the mold to a designer’s specifications before curing the desired composite matrix on it.

van der WerffImka Westerhuis

Launched in August 2022, Petronella was the first wooden boat Van der Werff and Bergsma built from pre-formed hull panels.

Van der Werff’s Proof of Concept

Petronella is the demonstrator for Van der Werff’s evolving build method. The 24 (7.3m) weekender motoryacht was built to order for a Dutch customer who liked the idea of reinventing wood as a boatbuilding material. Cutting and placing molds and frame layout for the boat were done by traditional methods. The hull skins were produced at Curve Works, some 160 km (99 miles) from the yard. Because Curve Works’ adjustable mold was limited to 3.6m (11.8 ), panel size was restricted to that length. Back at the yard the preshaped hull panels were fitted over the molds and then glued to the frames and to each other.

The boat was launched in August 2022 and has been sailing ever since. Its electric propulsion further expresses the intent of this weekender motor­yacht to reduce emissions.

Strips or Double Skin?

When assembling multiple pre-curved wood panels into a hull there will inevitably be seams where they meet. “How we bond the panels and secure the seams depends on the size of the boat we are building,” Van der Werff says. “The Bamboo Ark will be built using a single layer of three-dimensional curved-bamboo panels. These will be 2cm thick [0.79]. We have the panels made a bit too long as we want to mount them over the mock-up [molds]. To close the seam, we glue the panels together and take the part of the panel that we saw off to use as a 12cm [4.8 backing] cover on the inside of the hull. This piece of panel will have the exact same curvature as the hull part for which we use it.”

Larger boats will be assembled from two layers of pre-curved panels. In the design phase, by ensuring that the panels have generous overlaps, the seams will not be a problem or require additional reinforcement after the panel layers are glued together. “We did this with hand layup on the first hull,” Van der Werff says, “but we will start doing this by using vacuum infusion for the next.”

van der WerffImka Westerhuis

The builders experimented with black Sikaflex rubber adhesive between the hull panels to compare with epoxy-bonded panels for impact resistance and strength.

Lab Testing

The boatbuilders are experimenting with rubberized adhesives as a bonding material compared to conventional epoxy glue. Sikaflex rubber glue will remain flexible over its lifetime, whereas epoxy is rigid. So which bonding material will result in the strongest hull panels?

Van der Werff: “We made a panel using rubber and a panel using epoxy and took it to the Lucht- en Ruimtevaartlaboratorium [aeronautical and space lab] for strength testing. A sharp metal weight was taken to ever-greater heights and then dropped on the panels to determine their point impact resistance. We got the best results from a sheet of wood bonded with rubber and having a layer of Kevlar weave in between. The sharp object falling onto it from considerable height did cause a dent, but the panel was not leaking after this impact. That is the most important result for a boat, of course.”

The Local Forestry Challenge

In production, the boatbuilders’ environmental goals are not being achieved yet. “There is not yet production of bamboo here in The Netherlands,” Van der Werff admits. Fast-growing stands of bamboo (a grass) will easily grow in northern Europe, but no large-scale agriculture effort has developed. Bamboo of the desired quality must be imported from China. “We need polder bamboo,” the builder says, referring to the low grounds of The Netherlands where most of the agriculture is located. “Although the bamboo has absorbed a lot of carbon dioxide when growing, transporting it from China to Holland is making an impact on the environment that would not be necessary if we grew bamboo here,” he says.

There’s a similar problem with Accoya. The ideal tree that provides wood for the curing process of Accsys is the radiata pine harvested in New Zealand. Again, shipping wood from the farthest possible destination from The Netherlands does not contribute to sustainability. This species of pine also could be grown in Europe. Indeed, some first harvests of radiata pine could be imported from Spain, while other species of similarly fast-growing pine already in Europe could be harvested and treated.

Van der Werff to Scale the Effort

“After traditional wooden boatbuilding was marginalized to become heritage, the last attempt to use wood as a boatbuilding material has been wood/epoxy construction,” Van der Werff says. “This method, in spite of creating lightweight, strong, and low-maintenance boats, has not become popular. GRP is still the dominant boatbuilding material. We want to demonstrate that better and more sustainable use of materials is possible, and we find that wood provides a good alternative to the conventional composites. We have demonstrated that our technology works. We aim to proceed on a larger scale.”

About the Author: Freelance journalist Hans Buitelaar, who lives in The Netherlands, specializes in yachting and the maritime industry, focusing on technology and sustainable innovations.