Originally written for Professional Boatbuilder Magazine.

Developing, designing, refining, and marketing Windrider’s line of 10’–17’ (3m–5.2m) rotomolded polyethylene trimarans.  

by Jim Brown

The takeover of the America’s Cup by multihulls in 2010 has spurred speculation over what influence the next major Cup competition, in 2013—and its attendant media blitz—will have on recreational sailing, especially in multihulls. Some say the Cup will help it; others think it will hinder. But with the economy still gasping, catamarans and trimarans large and small seem positioned for once on the up side of the boating industry where there’s still some investment and, perhaps more importantly, growing public interest.  

Dean Sanberg, new owner and president of Windrider International, a company that manufactures a 15-year-old line of rotomolded polyethylene trimarans, is poised to benefit from any surge in demand for recreational multihull sailing. The businessman and investor first saw a Windrider 17 (5.2m) trimaran pulled up on the beach in Belize in 2009. With an extensive background in marketing—and despite zero knowledge of sailing—he took a long look at the little trimaran and thought, I can sell that.  By summer he had bought the company at a fire-sale price and set to work revitalizing the Windrider line of boats and its beleaguered dealer network.

Windrider trimarans have a checkered past. The brand was spawned in the mid-1990s by the aggressive kayak manufacturer Wilderness Systems, which would eventually become part of today’s behemoth Confluence Paddlesports. But Windrider was always an anomaly in a paddle-driven empire, and it suffered from corporate neglect and misunderstanding along the way. 

It happened like this:

“We got into the boat business by building whitewater kayaks for ourselves in my garage,” said Andy Zimmerman, former CEO of Wilderness Systems. “They were those minimal squirt-boats for going over waterfalls and spending lots of time paddle-swimming around beneath the surface in the bubbly. Pretty soon we were making them for others, but when squirting tapered off, we got into making sea kayaks. Soon we had a little factory.” 

John “Shep” Shepard was Zimmerman’s business partner through the late 1970s and ’80s, when the kayak went mainstream. “Andy and I had a simple division of labor,” says Shepard. “It was my job to get the boats out the door and his job to sell them. And no matter how many boats our people produced—sometimes hundreds per week—it was never enough.” 

Zimmerman recalled, “It was getting to be more like a business than a blast, and I figured that so long as we were doing business, we may as well make some real money. The only way to do that was to get into rotomolding, and that would take some real money.” 

In about 1980, Zimmerman and Shepard were approached by Andy Scott, a college professor and boating enthusiast. He was impressed by the vitality and commitment of the Wilderness Systems “tribe” and their shop, and he told them that if they ever needed money, they should let him know. Months later, with no more security than a handshake, he wrote them a check for $250,000. They immediately invested it in their first rotomolding oven, which was soon to set the entire paddlesports industry on its ear. 

The Sea Kayak of Sailing

“We were doing fine,” said Zimmerman. “But we were in the boat business to have fun, and after eight years of looking at thousands of kayaks and busting our buns to build them and sell them, it was getting old. Just to play around, we started putting little sails on them, and soon realized that kayaks were too tippy to be sailed unless we also put outriggers on them. Now that was really fun.” 

By happenstance I bumped into Zimmerman at his company picnic in 1980. Held at Cedar Island on North Carolina’s Albemarle Sound, this annual shindig was staged partly to get all Wilderness Systems employees out on the water to experience the products they were building. I was surprised to notice, among their armada of colorful products, an appealing little trimaran. Its central hull was a stock kayak, and it had a single, lovely gull-wing crossbeam with small outrigger floats and an unstayed sailboard rig. I learned that it was “just a prototype,” but asked if I could try it on the water. Upon returning to the beach, a mutual friend introduced me to Zimmerman and Shepard. They all asked me what I thought of their “Kaimaran.” 

“Nifty,” I said. “It’s great in this flat water and these balmy breezes, and maybe that’s what you want. But I bet when you take it out into the wind and chop, it wants to be a submarine.”

“That’s it,” said Zimmerman. “We’ve learned that kayaks are designed to be pushed through the water by the strength in your arms, whereas sails can be a lot more powerful than that. We want to add a line of sailing products to our paddlesports stable, but this prototype has shown us that we don’t want just a sailing sea kayak. What we want is the sea kayak of sailing.” 

Then he asked if I would design it.

Before creating a new production boat, especially one to be built in a material that was alien to me, I had a lot to learn about polyethylene and the client, Wilderness Systems. We met at the company’s factory in Greensboro, North Carolina. Zimmerman said, “We know that the sailing marketplace is tiny. It is almost an elite, sectarian sport, so to sell sailboats in anything like the kind of numbers we’re accustomed to with kayaks, we’ve got to expand the market base. By contrast, kayaking is huge—they’re almost a commodity. So I think we should establish some overlap between sailing and paddling. We need a gung-ho little trimaran that you can sit down inside of and steer with your feet like a kayak, and we’ve got to be able to sell it for $2,999.”

  I responded, “From 20 years of trying to sell multihulls, I can tell you that sailors tend to be rather hidebound. They want to stay with what has always worked for them.”

“Never mind,” interrupted Zimmerman. “There aren’t enough traditional sailors out there anyway. I’m trying to tell you that we need a product that will expand the market base.… I don’t care if it doesn’t even look like a sailboat, because we’re going to sell it to people who wouldn’t normally consider having a sailboat. Use your imagination.”

“What if this product falls apart or fails in the marketplace?” I asked.

Shepard replied, “We don’t even consider the possibility of failure, because that would take all the fun out of it. So get over it and design us a real no-worries boat.” 

Design

This was a fabulous opportunity, but I was scared. Besides the structural challenges, which I considered to be unprecedented because of the flexible material and the multihull’s sprawling platform, I had to come to grips with the extreme freedom of form possible in rotomolding. It seemed that any shape that could come out of the mold was possible with this material. With no hull-to-deck joint required I really was faced with designing boats that were like bottles. This challenged my abilities of topological visualization to the extent that I couldn’t draw the boat; I had to start with models. 

It took three months and three fiberglass scale models, with a separate trip to the factory with each, for us to arrive at the configuration that Shepard thought he could build and Zimmerman thought he could sell. That boat would eventually be called the Windrider 16 (4.9m).

To come close to the required price point and to compensate for the difficulty of rotomolding a centerboard trunk, I opted for a long, shallow, fixed keel on the main hull and a molded-in rudder port for a non-kick-up rudder, features I knew would compromise performance in light airs. I designed the main hull and floats with wave-piercing bows, a form that has become common among racing trimarans today. The crossbeams were to be aluminum tube bent in a graceful high curve quoting the traditional trimarans of Bali. 

After translating the boat from the model onto paper, we spent months in the R&D shop, building the strip-planked plugs of the hull and float in full size. We pulled a crude fiberglass prototype off the plugs, and test-sailed it in a small lake, with grand results. 

After more weeks of sanding and finishing, and despite the feeling that we were jumping into the unknown, we took the giant leap. The final plugs were shipped off to the specialized foundry, where the aluminum production molds were cast at a cost (in 1995) of about $160,000. From these three molds (two of them identical to produce both float hulls in a single oven cycle), the first pre-production prototypes were molded and then assembled with their crossbeams and sailing rigs. 

Shaping those crossbeams required investing in a special sweep bender, and taught us a lesson in metallurgy. The first T6 aluminum applied readily bent and performed well in service on the first hundred boats. As that original batch of raw stock aged, however, it became harder and then impossible to bend to the designed shape. We substituted T5 aluminum and had no further problems. 

The aluminum masts on the early boats were in two telescoping sections, and the boom required a specialized gooseneck that allowed the sail to be rolled up on the mast for infinite reefing, and stowage. 

We took these first two boats to the notorious Oregon Inlet on the North Carolina Coast for sea trials. With the wind blowing in against a strong outgoing tidal current, and the inlet showing patches of breakers, we launched our plastic trimarans, repeatedly charged into 4’–6’ (1.2m–1.8m) overfalls, and always emerged unscathed and surprised. We were sitting down so low that we felt we were wearing the boats. We could drag both elbows in the water while steering with our toes on the foot-pedal rudder controls common on sea kayaks. When riding surf, the sensation of speed was intense, and because of the innate flexibility of polyethylene, we could see the platform and even the hulls twist and wiggle through the seaway, which seemed to soften the ride. With our shallow rudder I was concerned about responsiveness of the helm, but even steering downwind was crisp enough. 

The following week we redesigned the maststep assembly to better handle the leverage of the unstayed mast. Otherwise, the structure, despite many inundations and even being nailed to the sand by thumping breakers, proved virtually bombproof. I came away with newfound confidence in polyethylene.

To Market

The Windrider 16 was released to dealers in 1996. At about $3,000 retail, nobody complained about the price, but the boat earned mixed reviews. “Some people really love the looks of that thing,” one dealer told me. “But others don’t know what to make of it. It is so spacey-looking, so off-the-wall that they think it comes from another planet.” 

Zimmerman had assumed his kayak dealers would distribute the Windriders, but there was some resistance as the little trimarans took up too much showroom space and didn’t appeal directly to paddling aficionados. But he didn’t lose confidence: “For dealers who can handle them, all they have to do is get someone to step up for a demonstration sail, and the thing is sold.” 

Keith Zwart, sales manager for the brand, wisely began introducing Windriders to established sailboat shops, where the boats found ready admirers. Current company records show 1,200 of the 16s have been sold since 1995. 

Perhaps because of its appearance, Windrider soon established a distinctive personality in the boating marketplace. Word got around of its essential differences: The pilot sits down inside the craft in a padded armchair, somewhat protected from the wind, steers with his feet, has both hands free for sheeting, always faces forward, keeps his head well below the boom, and never has to shift his weight around to stabilize the craft. The old excitement of hiking out to “hotdog” the boat along the ragged edge of capsizing is missing, but in its place comes real security and relaxation. At first, some experienced sailors said, “It’s too easy,” but if they took the chance to get out in the wind and waves, they often came back wanting one. And as Zimmerman had intended, the boat was a hit with nonsailors. Among the early reactions were comments like “Fun at any skill level,” and “Most of the speed but twice the comfort of a Hobie 14.” 

The armchair sailing ergonomics seemed to facilitate learning to sail. I remember how John Britt, owner of Norbanks Sailing, a busy rental operator also located on the North Carolina coast, explained it: “In a dinghy, beginners have to get used to steering with a tiller, which is counterintuitive. The boat turns opposite to the hand motion. So, while squatting in the bilge, facing forward to see where they’re going, they have to reach behind and steer backwards. Next, while tacking they have to rapidly shift their body weight from one side of the boat to the other, scrambling under the boom, just to keep the boat from tipping over. And then when jibing they have to handle all the sheets with one hand and steer with the other, and crouch down to keep from getting whacked on the head by the boom. Of course it’s all in the normal act of learning to sail, but it can be daunting for the beginner, and a real pain for the rental operator.”

“And in the Windrider?” I asked.

“I can send absolute greenhorns out, even when it’s gusting hard, with no more instruction than, ‘Push right to go right, and don’t try to sail straight into the wind.’ They can go out for an hour or three, have a blast, and they can always get back by themselves. I don’t have to chase them all over Pamlico Sound in my crash boat, recover capsized boats, and tow them home loaded with wet, scared, never-again customers.”

Certainly the Windrider 16 had met Zimmerman’s design brief for an affordable and accessible trimaran, but it took an old-salt friend of mine to evaluate my design knowledgeably and objectively. After wringing it out in ocean waves, he said, “This thing tacks dependably, and she’s weatherly enough when the wind blows, but in light airs she’s mushy coming out of a tack because there is no centerboard. Her shallow rudder contributes to that mushiness, but when she gets going, she steers and climbs to windward well enough. The main thing is that when the wind blows, she wants to be reefed to keep the bows from diving, and even then she throws a lot of water. But she can also take a lot of water with no white knuckles, and sailing her, whether in zephyrs or in squalls, is a real joy. I’d say she is not a perfect boat, but she’s a great buy.” 

I also identified that shortcoming of the tendency of the low-buoyancy wave-piercing bow to dive at speed. This behavior wasn’t disastrous in the 16, because there was no foredeck for the boat to trip over, and bow diving could be easily avoided by reefing the sail. But it troubled me as a designer and taught me a lesson: a fiberglass prototype doesn’t truly represent its as-yet unborn polyethylene offspring, because the two materials shrink very differently during cure. Conventional wisdom is to count on 4% shrinkage in rotomolded polyethylene, but the actual amount of shrinkage also depends on the shape of the structure. Where the topsides of this boat’s wave-piercing bows converge at acute angles at the keel and the kingplank, they tend to draw the hull sides in upon each other during cooling, and this deprives the forebodies of some reserve buoyancy and of the slightly convex curvature I had designed in, and that existed in the fiberglass prototypes. 

Windrider 17

Sales of the Windrider 16 almost covered the initial investment in just a couple of seasons, so by 1999, Zimmerman and Shepard started pressing me for another design. “You can’t make it in the marketplace with just one or two designs,” Zimmerman said. “You’ve got to have an integrated product line to convince the buyers that you’re leading the way.” 

It wasn’t difficult to imagine the next step. The 16 is essentially a solo boat, and dealers were calling for a tandem-seat Windrider. We had learned a lot developing the first boat, and there had been no structural failures, even in the brutal livery service into which many had been sold. Still, I was reluctant to rotomold a larger craft. Because the hulls cannot have an internal molded skeleton, they are dependent on compound curves and stiffening ridges to create eggshell rigidity in a structure that’s otherwise more like a squeeze bottle. 

Then word came down from the Wilderness Systems marketing department: “If we’re going to go for a larger Windrider, it had better be able to carry a family of four.” That meant a payload of about 600 pounds, compared with just 200 in the 16. This meant a much larger molding, higher freeboard, deeper bilges, a foredeck one could walk on, and a much more powerful rig and sail plan. Any hull with higher topsides and a deck would necessarily have much wider “flats” in its forebody, and this would really invite panting (deflection inward from hydrostatic and slamming stresses) of the polyethylene. At the least, something had to be done to support the main hull from the inside. 

To counter this problem I designed a separate sole, or floor, panel running full length down the hull at about mid-height between the bilge and the deck. The floor itself could be made of flat-sheet plastic, heat-formed with corrugations to achieve walk-on stiffness. It would provide the necessary platform for tandem seating and forepeak storage. To receive this floor, the hull could have a full-length chine or spray lip protruding outward just above the waterline. This chine would create an internal shelf to receive the floor, which could be installed in three segments through the cockpit openings. The floor would cut the panting spans in half with firm support inside. 

Another decree from management was that this new boat employ the float hulls from the 16. That meant that the fore-and-aft distance between the crossbeams in the new boat had to be the same as in the 16—not enough space to locate tandem seats in the main cockpit. Despite my firm objections they stuck to their guns, and with much trepidation, I proposed locating a separate pilot’s [helmsman’s?] cockpit aft of the after crossbeam. This would free up the main cockpit for use as a footwell so that the whole clan could sit around on the trampolines without squatting. However, the pilot’s [helmsman’s?] weight would be located so far aft that to support it the hull’s underbody would have to be grossly distended near the stern. The design was in danger of being seriously compromised by these totally nonarchitectural dictums, and I considered pulling out. 

Mike McGary saved the day. A strong [An experienced?] sailor and engineer, he was hired on as technical director for the Windrider division. McGary gave me the confidence to stick with the project. 

“Jim, they can’t foresee that the old floats will make the new boat a dud,” he said. “So we’ll just have to build one that way to show them. Go ahead with the main hull just the way you want it, and we’ll get our new floats eventually.” That’s the way it happened, but it required the extra time and expense of prototyping the dud. 

To avoid the pitfalls of fiberglass prototypes not being directly comparable to a rotomolded product, we created a so-called pre-production, polyethylene prototype. To do this, we pulled “temporary” molds of fiberglass and a special heat-resistant resin off the plug. Such molds can be subjected to the minimum heat necessary for rotomolding (if only for a few oven cycles), which allowed us to build a polyethylene example of the final product. It is rather crude and not fully “cooked,” but it’s good enough for initial sea trials and to assess the effects of shrinkage. The 17 required three developmental prototypes, each with trips to the coast for trials, before the company invested in the cast aluminum production mold.

The 17 also required a new approach for the tubular aluminum crossbeams. On the 16, collapsing the components for trailering was accomplished by disassembling the beams into four loose sections. On the new boat, crossbeams telescoped inward to create a legal trailering width; and the floats, permanently attached to the crossbeams, remained integral with the main hull—whether sailing or trailering. This helped to expedite setup and breakdown, which in the new boat was complicated by the addition of a stayed rig. 

Another significant difference in the new boat was our decision to attach the trampolines to the main hull sheer and carry them forward all the way to the bow. By knocking down the spray, these tramps made the boat much drier at speed. 

As McGary had predicted, we got our new, larger floats, which made the boat remarkably safe. The 17, like the 16 before it, was constrained by the necessity for a fixed keel and its non-kick-up rudder; any attempt at the alternatives would add at least $1,000 to the boat’s price. This meant, of course, that the 17 was also a bit mushy in light airs and tricky to launch through the surf.

In 2002 we introduced the new Windrider 17 at about $5,000 retail. The editors of SAIL magazine, after reviewing trials in the hands of their professional “test pilot,” judged this boat to be “practically impossible to capsize.” That pronouncement sold more boats than all the company advertising combined. Company records indicate that about 800 of the 17s have been sold to date.

Assessment

In spite of that success, as designer I have several niggling complaints with the 17:  

• To minimize cost, the 17 does not include spars running between the crossbeams for attaching the outboard edges of the trampolines. This leaves the tramps a bit saggy, and one’s bottom vulnerable to getting licked by a surprise wave top.

• The steering foot pedals are a bit draggy, which deprives the pilot of sensitivity in the helm.  

• For outside storage with the mast up, the jib needs a leech/foot sun cover to extend its life.  

Nevertheless, for 10 years the Windrider 17 has been the mainstay and real survivor of the product line, and there are still a lot of 16s out there, revered by their owners. As intended, many folks have had great fun in these affordable boats. My two Windriders still shape a big part of my personal sailing life. My own 17, the original pre-production prototype, has been sitting in the sun year-round since 2001. It shows many signs of use and abuse, but no evidence of degradation from exposure to the elements. Furthermore, we have pushed the 17s down the California coast and the Sea of Cortez on unforgettable adventures and expeditions with no structural failures (see the half-hour video “Riding the Wind” on YouTube and at www.outrig.orgw.outrig.org).

Sellout

The Windrider story would be neither complete nor fully useful to professionals without some mention of its business warts. My personal friendships with Zimmerman, Shepard, and their original team remain close, but I have seen their lives and mine dramatically altered by their decision to sell their company. 

About the time the Windrider 17 was released, management was committed to developing two other sailing models—neither of them my design. With their typical positive attitude and ambition, Zimmerman and Shepard undertook to offer “sailing with the laws of flight” in an affordable consumer product. Their astounding Windrider RAVE is a 16’ two-seat sailing hydrofoiler with rotomolded hulls. This 30-knot pterodactyl designed by Sam Bradfield and his team was introduced in 2003. Even with some 800 items on its parts list it was priced at less than $10,000—a truly splendid technical and production achievement that set the sailing world buzzing.  And shortly thereafter they [the company?] released their [its?] Windrider 10 (3m), a cute-and-capable “trimaran Sunfish” designed by Mark Balogh that, at a mere $1,999, belongs at any kids’ regatta and sailing school. Unfortunately, both of these designs had relatively brief production runs.

While everything was humming along, with four products in their [its?] sailing division and the paddlesports lineup selling something like 75,000 units per year, Wilderness Systems was approached by investors who were in the business of buying and selling companies for profit. After a sad three-year sequence of management shifts, investor flips, noncompete contracts, and a highly leveraged buyout, Zimmerman and Shepard learned the hard way that these so-called capital management outfits often make their money by squeezing the life out of their acquisitions, cutting staff, and inflating profits, just to sell again and move on. The old Wilderness Systems morphed into Confluence Watersports, which was then merged with the Watermark competition to become the undisputed world champion kayak mill. 

Windrider, which was never as profitable as the kayaks, didn’t fit in the newly consolidated paddlesports empire. Declines in customer service and dealer support caused distribution to collapse, and by 2008 Windrider’s assets, molds and all, were ready to be sold for scrap. 

They [The assets?] were rescued by a group of hobbyist retirees who bought the stuff and trucked it off to a new production site. They discovered that the main hull mold for the 17 wouldn’t quite fit into the oven of their new contract rotomolder. They summarily amputated 2’ (0.6m) from the mold’s posterior, and arranged to have it molded as a separate “floatation transom” that was later tacked on to the truncated hull. With no experience of differential shrinkage (and reluctant to consult the designer), they performed the surgery with a steeply angled slice. Consequently, the "butt splice” shrunk differentially between the two parts, resulting in a misfit, and the opportunity for the surgery to include a deeper kick-up rudder was lost.  

The new owners also lengthened the  crossbeams of the 17 (the only model they produced) to make the boat wider and faster. This change in dynamics cost the craft its “practically impossible to capsize” advantage and made it too wide to telescope to a legal trailerable width. 

After two years, sustained only by modest sales of the 17, the remaining dealer base was decimated, and the Windrider assets again went begging. That’s when Dean Sanberg saw the fateful unit sitting on the beach in Belize and went looking for the source.

Since taking the plunge a year ago, Dean and Robert Sanberg (now a father-and-son team) have been revitalizing the company with good business practices such as focused marketing, customer service, dealer support, and just plain caring. It seems to be making a difference. Besides the mainstay 17, they have put the 16 and the 10 back into production, and if they can tread water for another year or so, they could be well positioned to benefit from the gathering wave of multihull enthusiasm being fed by the entire America’s Cup series. 

Meanwhile, Zimmerman’s and Shepard’s original vision of affordability, ease of operation, and appeal to buyers who are not traditionally sailors, remains as potent as ever. 

[SIDEBAR: Intellectual Property]

What a Designer Is Due

Andy Zimmerman and John Shepard at Wilderness Systems always honored my Designer/Manufacturer Agreement for 2.5 % of net sales of the Windrider models I’d created for them. But when the company was sold I had to pound the table to collect, which worked for a while. With sequential [subsequent?] sales of Windrider’s assets, however, the plot thickened and the barristers got into the act, and, as usual, that threatened to be a deal breaker. 

The practical lessons I learned along the way are these: The world is full of copyright infringement and intellectual property theft, because, for small businesses anyway, the legal cost to the “author” of defending his rights will almost always far exceed the value of any judgment he might receive. Manufacturers know this and sometimes choose to ignore these rights. From my limited experience, it seems the best way for a designer to collect residuals is to continue offering consultation and promotion[al?] services to the manufacturer on the basis of mutual trust, and to create a position for himself to hold the manufacturer’s feet to the fire in the court of public opinion. 

—Jim Brown

[End Sidebar 1.]

[SIDEBAR 2.: Rotomolding]

Rotomolding Basics

Polyethylene is arguably the lowliest but most ubiquitous of plastics, the stuff of Clorox bottles, garbage cans, and plastic bags. It possesses a rare combination of properties in its finished form: stiffness, resilience, imperviousness, and cheapness. Those make it an ideal material for everything from giveaway pill bottles to affordable boat hulls. Its plasticity allows it to be heated and shaped through numerous methods into even more shapes. 

Rotomolding is the method best suited to efficiently manufacturing small boat hulls from polyethylene. It is most popular in the mass production of canoes and kayaks. (Polyethylene’s substantial weight and lack of stiffness make it unsuitable for larger vessels.) Although well known to many readers of this magazine (see Professional BoatBuilder No. 29, page 33), the process warrants a brief description here.

A rotomolded boat takes shape in an expensive female mold that is simultaneously rotated and rocked inside a hot oven. The mold is split down the middle and hinged to open like a clamshell. Its inner surface describes exactly the outer surface of the product to be made inside it, plus a nominal 4% to allow for shrinkage of the polyethylene part as it cools immediately after molding. 

The mold itself—and here’s why it gets expensive—is made to withstand thousands of cycles of heating up to as much as 500ºF (260ºC), so it must be cast out of aluminum. Creating it is far more expensive and involved than building composite molds for production fiberglass boats. Investing in the aluminum tooling and its oven is done only with the assurance that you are going to be selling many boats. Once the mold and its attendant infrastructure are in hand, this process can really crank out cheap one-piece boat hulls that require minimal secondary assembly, such as attaching hull and deck units. It’s all in the mold, including the stiffening ridges, styling lines, graphics, and even the hatches and their covers, which are simply cut out from the molded part later. 

With the giant aluminum clamshell open, the process begins when a technician dumps in a measured amount of granular polyethylene. Looking like coarse sand, of any color, the raw plastic is carefully weighed to assure the right hull thickness for a given boat. 

Then the mold is closed, its tongue-and-groove edges are clamped together to prevent leakage, and it is moved by overhead crane into an industrial oven. Resembling a small shipping container, the oven receives the mold on its internal spindles, like a chicken on a spit. The oven door is closed, the heat is turned on, the aluminum mold gets hot, and the plastic inside starts to melt. The mold is then rotated slowly, distributing the puddle of molten plastic captured inside, and then the whole oven begins to rock from end to end. Its entire inner surface becomes evenly coated with plastic. Presto! Rock-and-roll [rock ’n’ roll?] molding.

As an example of the speed and expense of production, the main hull for the Windrider 17—one of the largest one-piece boat hulls produced by rotomolding—takes about 50 minutes in the oven and contains about $200 worth of plastic. When all the granular polyethylene has melted and been sloshed around, the mold comes out of the oven and is rotated above a bank of cooling fans. In a short time the clamshell is opened and out pops a boat.  

It isn’t that easy every time. It usually requires rejecting a few hulls to get all the production variables right, such as the temperature inside and outside the mold, the right number of rotations at the right rocking angle, and the correct amount of plastic to achieve the best physical properties for the least cost and weight in a specific molded part. At least the reject trials are recyclable, and if the oven operators know their stuff, soon the process can be converted to computer control. For kayaks, roughly seven hulls per shift can be removed from an oven for finishing details, and with multiple ovens molds and shifts, the boats can really add up. This isn’t boat making; it’s boat baking.

Advances in rotomolding have been made, especially in tailoring the plastic formulation to the part. Much larger products than boats are often rotomolded, and the process can involve additional steps. Where greater stiffness is required and additional weight can be tolerated, so-called dump box technology can add a structural layer of foamed plastic inside the layer of plastic outer skin. This is done by mounting a closed box of raw polyethylene inside the mold, and once the first layer has been heated and distributed over the mold surface, a technician triggers the box to open, allowing the new substance to be distributed inside that first layer. While effective, the technique is too heavy for use in [produces a part that’s too heavy for? makes the mold too heavy for? unclear] boat construction. 

—J.B.