Vacuum infusion as the closed mould process of choice on the Tartan 4700, together with premium clear gel-coat, supports 70% glass content in glass/epoxy components and 80% reduction in cosmetic repair at post mould. (Picture courtesy of Tartan-C&C Yachts.)
Vacuum infusion as the closed mould process of choice on the Tartan 4700, together with premium clear gel-coat, supports 70% glass content in glass/epoxy components and 80% reduction in cosmetic repair at post mould. (Picture courtesy of Tartan-C&C Yachts.)
Even on frozen water, composite (ice) boats come about, constructed with glass fibre composite shells made from Owens Corning’s Ultrablade fabric, originally formulated to reduce weight and thickness in wind turbine rotor blades. (Picture courtesy of Williams Infusion.)
Even on frozen water, composite (ice) boats come about, constructed with glass fibre composite shells made from Owens Corning’s Ultrablade fabric, originally formulated to reduce weight and thickness in wind turbine rotor blades. (Picture courtesy of Williams Infusion.)

Fibre reinforced polymeric composites have been floating boats for decades – from the most modest dinghy to luxury gigayachts and stealthy military ships – in interior features and hatches to decks, hulls, keels, bulkheads, masts, sails and rigging, rudders, propellers, even anchors.

The materials provide classic gains in strength-to-weight ratio, plus critical resistance to the specific wear factors that cause surface osmotic blistering (sunlight, moisture penetration and dockside or on water impacts). FRP also delivers tailored structure and integral features, along with fire retardance and aesthetic/cosmetic finish at Class A level, in part through a manufacturing evolution to closed moulding methods such as vacuum infusion.

Today’s lucky sailor can take to the waves in whatever strikes one’s fancy (and fits the boater’s budget): canoes to sportfishing convertibles, ferries to fishing trawlers, tugs and tow boats, skiffs and sculls to submarines, life boats to houseboats to battleships and beyond. Customer demand appears to waver between extremes of fuel efficient, ecologically ‘green’ boats and the unbridled opulence of jumbo yachts or performance-tweaked racers. One can but marvel at the massive eco-catamaran Turanor PlanetSolar; the world’s largest private staysail schooner Dream Symphony, and the international fleet of race-winning sailboats and yachts taking on the America’s Cup, Canada’s Cup, Volvo Ocean Cup and more.

The high-volume marine market has been tossed on stormy seas since 2007 – down 70% overall by some estimates. Stalwart boat builders are hanging on by downsizing and diversifying, and continue to improve the quality and performance of their products by using glass, carbon and aramid reinforced composites. Suppliers have focused new material science on marine applications with bio-resins, natural fibre reinforcement, carbon nanotube reinforcement, out of autoclave cure prepregs, 3D woven fabric and infusion-centric glass mat, low-emission marine polyester/vinyl ester resins and gel-coats, tooling pastes and resins for Class A surfaces, and new marine core materials.

Opinions vary among those interviewed here as to whether growth is coming in big boats or small boats, at what rate and off what shores, and when or if adoption of closed moulding processes for FRP will prevail industry-wide.

Closed moulding sea change

The primary method for composite boat building for decades, especially recreational boats manufactured in volume, has been hand and spray lay-up on a single-sided or open mould with polyester and vinyl ester resins and glass/aramid fibres. Polymeric gel and skin coats complete a laminate to help ensure and protect component surface finish.

Though open moulding offers advantages in labour and tooling costs, the process can be messy and is now subject in many countries to stringent health and safety regulations involving control of solvent emissions and airborne fibre particulate. A wide range of closed moulding processes has re-evolved from the early history of marine construction to address anew these very issues, and also offer significant weight reduction in composite parts. These are distinguished primarily by the exact manner in which resin is introduced into the cavity between two closed moulds and at what temperature and pressure, and encompass:

  • resin transfer moulding (RTM);
  • RTM Light;
  • vacuum assisted RTM (VARTM);
  • vacuum resin infusion moulding (VRIM);
  • vacuum infusion processing (VIP);
  • closed cavity bag moulding (CCBM); and 
  • the Seeman Composites Resin Infusion Moulding Process (SCRIMP).

Andre Cocquyt, president of composite R&D and manufacturing company GRP guru, Brunswick, Maine, USA, and an instructor in vacuum infusion for the American Composites Manufacturing Association (ACMA), identifies what he believes is the essence of the sea change from open to closed moulding processes: it all comes down to pressure.

“When the process uses negative pressure only, it is VIP,” he says. “When it uses positive pressure only, it is RTM; when it uses a combination of positive and negative pressure, it is Light/Lite RTM (LRTM). SCRIMP is a patented form of VIP, and the VARTM denomer is subjective: adding pressure on the resin can be as simple as raising the feed bucket higher than the feed field to create syphon pressure, or use of a mechanical pump to add slight positive pressure to the resin input. CCBM is simply reusable bagging with a form-fitted bag.”

Over his career, Cocquyt has been involved in the composite construction of North Sea fishing boats, race-winning sailboats, and a current client list including at least 20 boatbuilding OEMs.

“Many boat yards are using most of these closed moulding methods, since each offers advantages in the right context of product type, shape, size and number of parts,” he notes.

He also feels there are no significant technology barriers at this point related to closed moulding, “though there may be misconceptions regarding cost. Traditional open moulders may see the consumables needed for infusion (resin lines, vacuum bags and sealing material) as additional expense, but I think with careful study of ultimate bottom line, they could all be brought onboard.”

He gives testimony to the fact that “most or almost all of my customers who have embraced closed moulding and had it going prior to the recession have come through fairly well, and are now way ahead of the curve. They have new models, more efficient production technology and are back to hiring crews and filling their order books.”

The progress of closed moulding going mainstream in marine applications is also a central focus in Scott Lewit’s career. As President of Structural Composites, West Melbourne, Florida, USA, he has been studying VARTM for nearly 30 years, after founding his company and beginning to conduct business with the US Navy.

Moulding process selection is very part specific. Infusion processes are best suited for large parts such as hulls and decks or for parts that have specifications for high fibre content.
Scott Lewit, President, Structural Composites

“Although the use of closed moulding is advancing, the vast majority of watercraft are still being built with hand/spray-up methods,” he reports. “Larger craft over 35 ft are seeing a greater transition to infusion because the economics are much more favorable. Very small craft under 18 ft are slowly moving to VARTM processes, but growth overall is not at the volumes we have seen in the past.”

Lewit goes on to say that “moulding process selection is very part specific. Infusion processes are best suited for large parts such as hulls and decks or for parts that have specifications for high fibre content. RTM can be a good fit for small, mass-produced parts, whereas VARTM processes encompassing LRTM, VIP, and CCMB work well for small and medium parts in moderate volumes, providing the advantage of a cosmetic finish on both sides. A downside to these methods can come in design changes, which may result in complex tooling modifications.”

Structural Composites is currently working on construction of a lightweight combatant boat (7.8 m and 11 m) as part of phases II and III of a Small Business Innovation Research (SBIR) programme funded by the US Navy.

“Here the infusion process provides the repeatability and laminate quality required by the Navy,” Lewit explains.

“Using innovative designs with the infusion process, we have demonstrated a 40% reduction in structural weight without the need for advanced fibres. These efforts are also targeting development of coating systems to replace gel-coats. We’re formulating a new line of coatings that will allow us to tune elongation from 2% up to 100%.” (Elongation refers to elasticity behaviour that resists surface microcracking and hygroscophy.)

Yacht builder embraces VIP

The Chief Operating Officer (COO) of Tartan-C&C Yachts, Painesville, Ohio, USA, credits composites and closed moulding as crucial to his company’s ability to offer a 15-year osmosis guarantee on its boats, compared to the typical five-year guarantee.

Tracy Roskey has been in the composites business for 31 years, though he’s only been focused in marine applications as COO with Tartan-C&C for the past two years. He relays that within the total volume of composites manufacturing at Tartan-C&C, 70% is infusion, with the remaining 30% a hybrid infusion process used on decks, hulls, liners and large interior parts. This translates to over five C&C models and nine Tartan yachts utilising closed moulding, primarily vacuum infusion processing (VIP).

In 2007, we switched to VIP on the first Tartan 3700, which improved quality considerably. In the last 18 months, we have optimised our infusion process through tight control of viscosity, temperature, resin/catalyst ratio, processing time and cure rate, allowing only a 10% variation over the entire infusion cycle.
Tracy Roskey, COO, Tartan-C&C

“We originally started with hand lay-up and spray-up, went to wet bagging in 1999, but found the process messy and problematic dermatologically for our workers,” Roskey says. “We were also constantly fighting air entrapment in the laminate and wall thickness inconsistencies."

“In 2007, we switched to VIP on the first Tartan 3700, which improved quality considerably. In the last 18 months, we have optimised our infusion process through tight control of viscosity, temperature, resin/catalyst ratio, processing time and cure rate, allowing only a 10% variation over the entire infusion cycle. We take calibration shots before and after moulding each part in order to keep a finite operating range that delivers the best characteristics of the materials. This has resulted in an 80% reduction in repairs at post mould.”

Over the years, specific Tartan-C&C boats have come in as winners in the Canada’s Cup, Canadian Admiral’s Cup, Chicago Mackinac, Charleston Race Week and Key West Race Week. The raised salon Tartan 4700, introduced last year, reflects another change in production.

“We have the second 4700 build coming off the assembly line in May, and have switched to clear gel-coat rather than pigmented on infusion-moulded components,” reports Roskey. “This allows us to see all the reinforcement in both internal and external laminate to check for consistency. We’re finding that VIP helps us achieve a high glass fibre volume density, upwards of 70% on a single vacuum using our prop-rietary hybrid infusion process. Third-party assessors have declared our FRP consistency and density levels the best they’ve ever seen.”

“Composite hatches made via VIP that have previously taken a week to complete can now be manufactured in a day and a half,“ Roskey adds. “This is a huge quality upgrade and labour savings.”

Gel-coating can make or break a customer’s perception of a boat, giving Roskey a case for the premium clear-gel coat on the 4700.

“It is more expensive than a pigmented formulation in order to preserve water resistance, and our ability to verify reinforcement consistency may avoid a single service call per year,” he says. “That would offset the higher gel-coat cost for an entire year. Also, we use a bisphenol A epoxy resin, which results in dry Barcol hardness readings on our composite parts that are typically 10 to 15% higher than industry standard.”

He notes that highly bossed, detailed parts in deep or narrow component depressions create a special challenge for both molding and gel-coating.

“The weight of glass in seams makes it want to pull upward under vacuum, so we’re working on ways to double bag effectively and efficiently to keep materials seated during cure.”

Hand lay-up, in Roskey’s view, “is sort of like trying to paint a sponge in terms of effectively wetting out glass fibres. With infusion, we get suction at 1 atmosphere so our hybrid phenol-based epoxy resin coats and fills the voids between the fibres. This makes wet out so much better, you can’t beat it.”

From a market perspective, Roskey thinks a few more squalls may yet blow through.

“The inventory overflow of good used boats and unsold new boats is decreasing, but more OEMs and dealers are going to close or dramatically downsize. We introduced four new models last year, and are building at least one 40 footer every month. However, no two are alike because our business model walks a fine line between production and semi-custom output.”

Tartan-C&C Yachts manufactures carbon fibre masts and pocket booms as standard on its yachts. Roskey reports the OEM is currently working with its material suppliers on unique resin technologies not currently used in marine “that will take our glass impact resistance to new levels. We’re also addressing the maintenance costs of exterior wood, with development of new coatings and hybrid materials, including composites. Such material improvements can reduce the overall cost of owning a yacht, and improve the buy decision.”

Glass for Das Boot

Owens Corning (OC), headquartered in Toledo, Ohio, USA, has offered innovative products for closed moulding since 2004, notably FlowRo® fabric and Flowtex® fabric. Brian Chambers, Vice President and Managing Director for OC’s Engineered Solutions, comments that: “These products reflected major advancements that gave manufacturers a closed-mould knit product option to the transitional open-mould fabrics, one that works well in vacuum infusion processes.”

More recently, Owens Corning has introduced Uniconform® glass fibre mat and Multicore® for LRTM and CCBM.

“We have seen marine customers use these processes to make a range of products from small parts like hatches to larger parts like swim platforms,” Chambers adds.

“Custom yacht builders have embraced vacuum infusion with cored laminates and knit fabrics to produce laminates with high glass content in the range of 70-75% by weight.”

In addition to high glass content and cosmetic properties, OC glass forms for marine applications are answering another trend.

“Some of our customers are asking for more environmentally friendly or ‘greener’ components,” Chambers relates.

“Our Advantex® glass reinforcements are boron-free ECR glass that is stronger than E-glass, and made with our advanced glass melting technology that requires less energy and water and produces lower levels of fluorides and nitrogen oxide emissions. Manufacturers using Advantex glass in their composite laminates are making greener parts.” ♦
 


This feature was published in full in the May/June 2012 issue of Reinforced Plastics magazine.

Part 2 of this article is available here.