Methacrylate Adhesive Joins the Club

Boat bonding advances from weakest to strongest point

—by Patrick Shannon, nactional accounts manager, Marine Division, ITW Plexus

Vanguard Racing Sailboats of Portsmouth, RI, manufacture high-performance small boats for use in junior, collegiate, and Olympic sailing. The one-design racing format requires that all boats produced be uniform in design, shape, size and weight, within strict tolerances. The company’s most popular racing dinghy — the Club 420 — was introduced over twenty years ago and has gone through a constant process of refinement ever since. Recently, Vanguard made what is perhaps the most significant improvement in the boat since its introduction by dramatically changing the way in which it is assembled. All Club 420 sailboats are now assembled using Fiberglass Fusion methacrylate adhesives from ITW Plexus, Danvers, MA.

Battling constant use

Vanguard began building the 420 series of double-handed racing dinghies in the mid-1970s. Several colleges approached the company about the possibility of building a “beefed-up version” of the International 420, with the durability to stand up to the constant use and abuse of an institutional training environment. The result was the Club 420.

The C420 class of junior racing sailboats is used by over 350 sailing organizations in colleges, high schools and yacht clubs in the United States. Manageable for young sailors, the Club 420 enables them to learn teamwork, trapeze and spinnaker techniques. The stable and forgiving hull is built of reinforced fiberglass with high-impact bumpers and an untapered rig. Simple and safe for beginning sailors, the Club 420 is quick enough to excite even collegiate All-Americans.

The dinghy is built to provide years of service under the worst of conditions, designed to withstand constant use and inexperienced sailors, who may collide with docks and other boats, run aground or drop the boats. Patrick Muglia, production manager for Vanguard, observes, “We sell to the institutional market. Our customers demand durability. Some of these schools — the Coast Guard and the Naval Academies, for example — have these boats on the water five to seven days per week. The boats are constantly colliding as they go around the buoys.”

Problems with marine putties

By analyzing customer comments and warranty claims, Vanguard concluded that a disproportionate share of warranty work was a result of the marine putties used to join the Club 420’s FRP components. Over time, these putties became brittle and cracked, causing leaks and weakening the boats.

Upon closer examination, Vanguard found other problems with the fabrication techniques required to use the putties. Prior to application of the putty, the entire bond area had to be ground or sanded to improve adhesion. This task was time consuming, labor intensive, and introduced a high degree of variability into what was otherwise a standard manufacturing process.

The grinding process also creates dangerous airborne fibers that are a health hazard if inhaled. These microfine fibers easily become embedded in workers’ hair, clothing and skin. Consequently, workers must wear protective suites, goggles, filter masks and gloves while performing this task. Muglia notes, “The guys hate this job. They have to suit up. The suits and masks are hot, the guys sweat and their goggles fog up… Nobody wants to do it.”

Once the bond areas had been properly prepared, the polyester putty was applied manually. In other areas, bonds were created using the same methods that were used to fabricate individual components. The process involves spraying resins onto the mating surfaces, cutting and hand-positioning glass cloth, and then coating the cloth with more resin. Neither of these assembly techniques produced bonds strong enough to meet Vanguard’s stringent durability requirements for the Club 420.

Cutting preparation and bonding time in half

Always looking for ways to improve their boats, Vanguard decided to test Plexus methacrylate adhesives. The results of a flex test were dramatic — where a traditional bond failed after a number of cycles, the Plexus bond was so strong that the substrate failed before the bond. The test results were so impressive that Vanguard’s salespeople now use similarly bonded pieces of FRP to illustrate the flexibility and durability of the bonds to potential customers.

Vanguard originally estimated that using this adhesive would increase the manufacturing cost of the Club 420 by about $60. Chip Johns, president of Vanguard, notes, “On the first pass, we compared material costs only. This really didn’t give the whole picture. There are the labor savings, elimination of the sanding process and pads, and dramatically reduced warranty costs.”

Because this family of primerless adhesives requires little or no surface preparation, the boat company was able to virtually eliminate the time-consuming, dirty job of grinding and sanding bond areas. Muglia comments, “We used to have four people in the sanding department. Now we have only two and they work mainly on boats other than the [Club] 420.” The adhesives also require no primers, which has helped Vanguard significantly reduce the use of chlorinated solvents.

At first, the company used meter-mix dispensing equipment, but eventually chose to hand mix the adhesive and apply it using simple pastry bags — such as those used in cake decorating. The workers preferred the light weight of the bags and high degree of dispensing control.

The adhesives have sufficient open time to allow workers to precisely position larger assemblies, such as the deck and hull, yet cure rapidly at room temperature. They allow fixturing in less than one hour and cure to 75% of ultimate strength without heat or UV within two hours.

The company quickly found other uses for the adhesives beyond deck-to-hull bonding. Muglia observes, “You can do more with Plexus adhesives. You can bond dissimilar materials.” Rub rails that used to be riveted are now bonded in place. Muglia explains, “We used to use about fifty rivets per boat just to fasten the rub rails. The adhesives have eliminated the unsightly rivets every six inches on the rub rail as well as the ‘scalloping,’ which used to occur when the rubber rail expanded in the hot sun. It’s improved the appearance of the boat significantly.”

Muglia notes that in addition to enhancing the boat’s aesthetics, the use of adhesives to fasten the rub rails has reduced warranty claims. “Every rivet was a potential leak path,” he says. “The fewer leak paths, the fewer leaks.” He continues, “For the weekend pleasure sailor, leaks are a minor inconvenience. For a competitive racer, an extra gallon or two of water sloshing around the hull can mean the difference between victory and defeat.”

Reduced warranty claims

Vanguard warrants the Club 420 against defects in workmanship and leaks due to normal use for a period of one year. Despite this requirement of “normal” wear and tear, in many cases, there is no way to tell whether leaks are the result of general daily use or abnormally rough handling or impact. Muglia comments, “We’ve had boats returned for warranty repair where the impact force was great enough to unzip the putty joints for several feet.”

Obviously, the stronger the bonds in the boat, the fewer leaks and the fewer warranty claims.

Vanguard was impressed with the tremendous impact resistance of Plexus adhesives. In fact, more than 4.5 million thermoplastic automobile bumpers have been bonded by Ford using a similar adhesive without a single failure.

Johns comments, “Our deck-to-hull joint used to be the weakest point in our boats. The putty was the weak link in the entire system. Now, with the new adhesives, the deck-to-hull joint is our strongest point. The boat is really a one-piece system…a sort of monocoque assembly. It takes our product to another level…a higher level of quality.”

Muglia summed up his experience with the adhesives, “Since we began using Plexus adhesives, we produce better quality boats at a lower cost, our workers are happier and I don’t have to worry about warranty work.”

For years, the U.S. boatbuilding industry consisted of large numbers of smaller builders who produced relatively small numbers of boats each year. With recent consolidations, there are fewer, but much larger builders producing much higher annual volumes. In an attempt to streamline production, reduce labor costs, increase production output, and lower VOC emissions, many of these builders have turned to today’s new generation of structural adhesives.

Traditional boatbuilding techniques include glass-tabbing and marine putties, both of which are highly labor intensive, requiring sanding or grinding of substrates prior to bonding. Putties are typically highly filled polyester systems, inexpensive and excellent for filling large voids. However, their use requires sanding or grinding of fiberglass components to improve adhesion. In addition, putties are brittle and have poor elongation and impact resistance — properties which can lead to joint problems or failures after repeated cyclic loading such as that experienced during normal use. While new generation putties offer enhanced properties, their performance does not compare to that of structural methacrylate adhesives.

Fiberglass wet tabbing has long been used to assemble laminated marine components such as stiffeners, stringers, liners, and decks. The materials required for this process — resin and fiberglass — are readily available; however, the process is labor intensive. In essence, it is the same process used to produce the laminated components themselves — fiberglass tabs are coated with resin to join the components together. The strength of the joint is limited by the resin properties and the thickness of the glass tabs. Additionally, while this process produces strong, rigid joints, these joints offer very little flexibility. Since resin has very low elongation, high stresses are placed on the joint while under load, often resulting in failures.

Fiberglass tabbing comes with other considerations as well. To assemble components using this process, production personnel must have access and reasonable room to work. In certain applications where space or access is limited, the use of glass tabbing sometimes necessitates changes in the design of the finished boat to accommodate the assembly process. Finally, tighter restrictions on VOC emissions that result from glass tabbing have led many boat builders to replace traditional assembly methods with adhesives.

With the ability to produce durable, high-strength bonds to virtually all polyester resins and gelcoats, as well as most thermoplastics and metals, Plexus adhesives are changing boatbuilding. Their structural methacrylate adhesives chemically cross-link composites at a molecular level, fusing components into a unified assembly. The resulting bonds are so strong that the composites will delaminate before the bonds fail. Adhesive bonds offer superior physical strengths, flexibility, and durability as well as exceptional resistance to fatigue, vibration, impact, moisture, chemicals, fuels, and ultraviolet light.

Perhaps one of the most important benefits of structural adhesives is the effect they have had on boat design. By eliminating wood below the waterline (used to frame stringers and supports), adhesives have eliminated the potential for rot and other longer-term warranty problems. The flexibility of the structural adhesives not only distributes cyclic loading stresses that occur in normal boat use, it also dampens much of the impact of boats against water, producing a noticeably softer, smoother ride.

In addition to reducing plant VOC emissions by up to 90%, adhesive bonding also dramatically simplifies and shortens the assembly process. These methacrylate adhesives are primerless and require no sanding, grinding nor virtually any surface preparation, eliminating hours of tedious labor. They are easily applied and cure rapidly at room temperature. In fact, a typical stringer or liner can be bonded in as little as 20 minutes.