Composites in Boat Accessories and Hardware
Probably no other industry, to date, has seen such universal application of composite materials as the marine industry. It is common for boatbuilders to mold one-piece hull and deck structures in sailboats and motoryachts of all sizes and price ranges. In racing vessels and high-end yachts, composites are regularly used to form masts, rigging, spars and booms. Recently, composites have even penetrated sail fabrication (see CT's sister magazine High-Performance Composites, September 2005, p. 44). In search of ways to optimize weight savings and anticorrosion performance, boat manufacturers today are replacing steel, aluminum, bronze and wood with composites in a variety of boating accessories and hardware from stem to stern. Having gained huge weight savings with composite hulls and decks, boatbuilders are optimizing weight reduction "in all the stuff that goes inside,"quips Gregory Martell, managing director of Composite Boats Ltd. (Hibiscus Coast, New Zealand).
Cabinets & Countertops
In common with landlocked industries such as residential building construction and chemical manufacture, boatbuilders have used fiberglass showers and sandwich panel storage tanks for diesel fuel and fresh water, for more than 20 years - typically integrated into hulls. Since the turn of the 21st Century, however, boat designers have found ways to reduce weight yet retain the traditional look of boating amenities that might never see composites on shore. Prime examples are cabinets and countertops. Fiberglass substrates enable designers to incorporate what appear to be luxuriously massive stone countertops and fine hardwood cabinetry at a fraction of the weight of full stone thicknesses and veneered plywood. Martell notes that even in luxury models with genuine granite countertops, "if the base structure that holds this all together is fundamentally light, then the impact of loading in the luxury item is reduced."The result is the right look without all the weight.
Although Composite Boats Ltd., on request, has done a full build, its specialty is custom made-to-order interior and exterior components for boatbuilding clients. "For the type of parts we build, it has been accepted for many years that the use of composites is part of the design brief for vessels that are destined for above-average performance,"Martell says.
For its cabinetry, the company vacuum infuses sandwich panels, using three "universal"sheet aluminum molds. Custom part shapes are created by laying medium-density fiberboard or plastic inserts on the mold surface. The mold opening then is primed with paste wax (TR Industries, South Gate, Calif.) and, as a redundant backup, Safelease water-based liquid wax mold release (Airtech, Huntington Beach, Calif.). "This combination gives us the high-quality vacuum obtainable with aluminum molds, while creating 3-D shapes with very inexpensive, throwaway custom inserts,"Martell explains. In a typical layup, no gel coat is used. Instead, a peel ply is first down against the mold, followed by a 30g/1-oz polyester veil. Stitched biaxial (+/-45 ° ) E-glass fabric (430g/15 oz to 620g/22 oz) forms the panel skins, with 12-mm to 15-mm (0.47-inch to 0.59-inch), 80 kg/m3 (5 lb/ft3) rigid PVC foam core, such as Airex from Alcan Baltek (Northvale, N.J.). The biaxial fiber orientation in the skins provides torsional strength for stresses induced by the twisting of a performance-oriented vessel, Martell explains. Additionally, carbon unidirectional tape (Hexcel, Dublin, Calif., or equivalent) may be laid longitudinally into areas of anticipated high loads, such as the 90° corners of cabinets. In hinge locations, the sandwich structure incorporates wooden blocks in place of foam core.
When the part layup is complete, it is covered by a sheet of Airtech perforated plastic. The perforations allow the resin to flow into the dry fabric, and the sheeting provides for easy postcure removal of flow media and infusion plumbing. Last down is an unusual flow medium, a 50 percent agricultural shade cloth from R.J. Reid (Auckland, New Zealand), made by weaving plastic filaments to a specific density that partially blocks light. "The way they knit their fabric together provides a slow or fast travel orientation for the resin,"Martell explains. "So you can orient the flow media to speed resin transfer in one direction or the other.â€
The layup is vacuum bagged for processing by Composite Boats' in-house-developed Vacuum Assisted Infusion Lamination (VAIL) system, at a pressure between 12 and 20 millibars (0.174 psi to 0.29 psi), using high-temperature epoxy resin. Epoxy doesn't require a catalyst and provides better control over resin flow and cure times, compared to polyester or vinyl ester, Martell says. Vacuum bags and other vacuum gear are supplied by Vacuum and Blowing Services Ltd. (VABS, Auckland, New Zealand). After demolding, the surfaces are sandblasted and painted or surfaced with wood veneer. Similar fabrication methods are used for bunks, bulkheads, doors, steps, tables, hatches and other panel-type structural and nonstructural products.
Halfway across the globe, Beachcomber Fiberglass Technology (Stuart, Fla.) manufactures what the company bills as "maintenance-free"fiberglass cockpit cabinets, as part of its standard line of composite marine products for the recreational boating market. Beachcomber's cabinet panels are hand layed in open molds primed with Chemlease semipermanent mold release (Chem-Trend, Howell, Mich.) or Honey Wax, a carnauba-based, multiple-release wax from Specialty Products (Jersey City, N.J.). The exterior surfaces are gel coats matched to boat color, supplied by Cook Composites & Polymers (Kansas City, Mo.). The layup is a sandwich structure made from 42.5g/1.5-oz stitched biaxial E-glass mat sourced from China, with 51 mm/0.5-inch Divinycell rigid PVC cores from by Alcan Baltek. Most materials are sourced through the Lakeland, Fla. facility of distributor Composites One (Arlington Hts., Ill.).
For luxury yacht countertops, Stonwurks Div. of M&G Designs (Sylvan Grove, Kan.) offers its trademarked Strata Panels, which feature thin panels of natural stone laminated over a substrate of fiberglass/aluminum honeycomb sandwich construction. Stonwurks vice president Kirk Meyer says, "Natural marble and granite Strata Panels weigh 80 percent less than normal, full thickness stone (called dimensional stone) and offer greater impact and flexural strength."According to Meyer, any natural stone can be used. Panels are cut from 0.75-inch to 1.25-inch (19-mm to 31.75-mm) thick dimensional stone to 0.1875-inch to 0.25-inch (4.76-mm to 6.35-mm) thickness. Waterjet systems or CNC cutters with diamond blades can be used to cut the stone. Stonwurks prefers CNC cutting, using CAD DXF files submitted by the customer, or CAD DXF files converted from drawings or from plastic or wooden templates. Depending on the application, Stonwurks bonds the cut stone to a 0.25-, 0.5-, 0.75- or 1-inch (6.35-, 12.7-, 19- or 25.4-mm) composite substrate, using marine epoxy from Bonstone Materials Corp. (Mukwonago, Wis.). The most common applications feature the most lightweight combination: a 0.1875-inch/5-mm stone skin bonded to a 0.25-inch/6.35-mm substrate.
The substrate is Panel 302 marine board, a premanufactured sandwich structure made by Plascore Inc. (Zeeland, Mich.). Plascore uses woven biaxial glass outer skins pre-impregnated with flame-retardant epoxy resin and cored with corrosion-protected aluminum honeycomb. Prepreg is supplied by J.D. Lincoln (Costa Mesa, Calif.). For panel construction, the prepreg is layed up on both sides of the core and the flat sandwich panel is placed in a press preheated to 300°F/149°C to 350°F/177°C, which cures and bonds the prepreg to the core.
Stonwurks' specialty is seamless edges. "We do not cut the stone off and then laminate it back on,"Meyer explains. "We leave the stone thicker at the front face or other edge, and remove more stone behind the edge where it needs to be thinner for bonding to the substrate.â€
Stonwurks employs similar techniques not only for countertops but for wainscoting and other stone detail in aircraft and luxury motor coaches as well.
Fiberglass began to replace corrosion-prone bronze, aluminum and stainless steel in plumbing fixtures in the late 1970s. A producer of recreational boating accessories for more than 40 years, Robert Fores-man, founder/owner of Forespar Products Corp. (Rancho Santa Margarita, Calif.), was an early pioneer. "These metals are subject to electrolysis/corrosion in saltwater, explains Art Bandy, Forespar OEM and international sales manager. "Over time, a natural degradation of the metal will occur and this can be greatly accelerated if a stray electrical current is present."Bandy says Forespar Marelon plumbing components have been installed in "several hundred thousand vessels,"worldwide.
One of Forespar's most successful efforts resulted in composite seacocks. Seacocks are used to close off "through-hull"holes drilled for engine shafts or other equipment, preventing water intrusion if the hole is, for some reason, left open. Forespar R&D brought about a proprietary formulation of long fiber-reinforced nylon, compounded by DuPont Engineering Polymers (Wilmington, Del.) and based on DuPont's Nylon 6. Trademarked Marelon, the injection-molded material forms the only synthetic seacock valves tested and approved by the Marine Underwriters Laboratory (UL) and accepted by the American Boat and Yacht Council (ABYC), Bandy says.
Spinnaker & Whisker Poles
The 1970s also saw the first use of carbon composite spinnaker and whisker poles. A spinnaker pole is a spar attached at the base of a mast with the end attached to the spinnaker (a triangular sail), to support it away from the sailboat when sailing downwind. The whisker pole is a lighter version of the spinnaker pole that serves the same function for a jib. The latter may be adjustable in length. Forespar sought a better alternative to the aluminum tubes and cast aluminum ends initially used for its spinnaker and whisker poles. In fact, Bandy claims that Forespar made the world's first telescoping whisker pole for sailboats. Carbon poles are used in virtually all classes of sailboats. Forespar also makes injection molded Marelon end fittings to replace the aluminum fittings on pole ends, reducing by half the total pole-and-fitting weight and eliminating potential corrosion due to electrolysis that could occur between the carbon pole and aluminum fittings.
Since the mid-1990s, a trend led by America's Cup and Grand Prix Yacht Racing teams has seen composites gaining acceptance even in highly loaded hardware, such as sailboat winches, blocks, masts and rigging. Harken (Pewaukee, Wis.) first proved its composite fittings in the 1995 Americas Cup race in San Diego and "became an established leader in composite hardware supplies for the 2000 event in New Zealand,"according to Bill Goggins, Harken's marketing manager.
Technology validated at these high-profile events is often adopted elsewhere in the industry. Harken's Carbo line of composite blocks (pulleys) and fittings, for example, are considered a major advance in boating, Goggins claims. Made from injection molded long glass fiber-reinforced nylon, Carbo blocks are, he says, "the first significant breakthrough where metal is not required for anything structural to hold the loads."They are an option to Harken's Classic-series blocks for small boats, which feature unreinforced DuPont Delrin acetal resin in the sideplate, with a stainless-steel strap for strength. With fiberglass reinforcement, the Carbo blocks require no steel strap and, therefore, are 30 percent lighter yet can handle a 50 percent higher working load than the Classic series - 500 lb to as much as 750 lb (227 kg to 340 kg). Designed for both racing and cruising sailboats up to 40 ft/12m in length, Carbo blocks are available with sheaves (the pulley's rotating grooved disks) sized from 29 mm to 75 mm (1.14 inches to 2.95 inches). "By eliminating the stainless-steel strap,"says Chuck Lob, Harken's production engineering manager, "we eliminated concerns about corrosion and, at the same time, reduced the weight and assembly part count, saving production costs.â€
Composites also are charting a course into another highly loaded component, the winch used to haul in sails. In America's Cup and Grand Prix racing, powered equipment is not permitted. Winches must be hand-operated. Two grinders (crewmembers) turn the winch handles on the pedestal. America's Cup teams have linked as many as four pedestals to a winch for specific maneuvers. Primary headsail winches and mainsail winches can be subject to 12,500-lb (5,500-kg) loads. Harken manufactures carbon/epoxy sailboat winches and pedestals at its plant in Lurago Marinone, Como, Italy. The winches are in use on all of the America's Cup boats and many other top-line racing vessels, says Goggins, The reason for this success? "Greatly improved stiffness-/strength-to-weight ratios in critical areas on the raceboats, compared to the aluminum and titanium that carbon/epoxy replaces,"he maintains, noting that Harken's rule of thumb is 50 percent weight savings, compared to aluminum.
Carbon also is finding a place in deck components subject to the high stresses created by winching a sail. For a recent 2-ft by 2-ft by 4-ft long (0.6m by 0.6m by 1.2m) cockpit coaming (the raised edge designed to help keep out water), which had to support an attached primary sheet winch, Composite Boats Ltd. provided a structural sandwich of carbon composite skins and high-density balsa core, which then was glued to the deck of the vessel (see photo, p. 33).
Boarding Aids & More
Elsewhere, composites are replacing aluminum boarding ladders and gangways, also known as passerelles. GMT Composites (Bristol, R.I.) designs and builds boarding ladders, articulating stairs and gangways for both sailboats and motoryachts. GMT prefers carbon fiber as a stronger, lighter material, says GMT's president David Schwartz.
GMT built its first carbon gangway in 1994, when asked to design and build a boarding structure that would be lighter and easier to deploy than the existing aluminum unit on a 125 ft/38m yacht. Today, GMT builds gangways in custom lengths for 60 ft/18m and longer yachts. Lengthier gangways are designed to either fold or telescope to fit available onboard storage space. The lightweight units avert the need for a costly hydraulic boarding system and, further, are aesthetically superior to anodized aluminum units, Schwartz claims, noting, "They add grace and elegance to an otherwise ordinary yacht function.â€
GMT builds its composite gangways by hand layup of unidirectional carbon epoxy prepreg made by Newport Adhesives and Composites (Irvine, Calif.). The gangway deck is a structural sandwich with a Corecell foam core (Gurit, Magog, Quebec, Canada) constructed by hand layup in custom open molds that form both the gangway's deck and siderails. The layup is vacuum-bagged and cured at 250°F/121°C in a computer-controlled oven. After cure, the gangway deck can be painted or covered with teak or teak grate. Ladder rails are layed up over mandrels made by MGB Machine Shop (Bristol, R.I.) and either painted or clear-coated "to let the beauty of the carbon shine through,"Schwartz says.
Composites design firm Exit Engineering (Fiesso d'Artico, Italy) segued from racing motorcycles to leisure boats in 2004 and, in collaboration with custom molder Re Fraschini Components srl (Legnano, Italy), markets carbon composite gangways (see HPC Mar 2006, p. 43) and patented, hollow monocoque steering wheels for sailing yachts (see HPC January 2005, p. 44). Although its primary market is the cruising sailboat, technical director Giuseppe Bottacin says Exit also offers gangways for motorboats. Exit recently introduced a 138-inch long by 23.6-inch wide (350-cm by 60-cm) model that is 50 percent wider than comparable products, but weighs only 29 lb/13 kg.
Re Frashini makes both master models and tooling, then hand lays gangway sections in a cleanroom. Each is a modified C-beam sandwich construction, with skins built up from unidirectional and 2Ã—2 twill carbon/epoxy prepregs supplied by G. Angeloni srl (Quarto d'Altino, Italy). Nomex honeycomb core (DuPont Advanced Fiber Systems, Wilmington, Del.) strengthens the walking area. Female molds fabricated from carbon fiber tooling prepregs are pulled from master models that are CNC-machined from TB 6720 epoxy tooling blocks (from Advanced Composites Group Ltd., Heanor, Derbyshire, U.K.). The layup is vacuum bagged and cured in an autoclave at 248°F/120°C for up to two hours. The precision model and tooling molds enable quality 101.5 psi/7 bar autoclave curing, which compresses the laminate, removing any entrapped air or resin voids and producing a finished part surface that mirrors the mold detail. This visible carbon finish is clearcoated with anti-UV paint (PPG Industries, Pittsburgh, Pa.), or painted in a color on request.
Higher End ... for Now
Although most of the above applications are limited to high-end yachts and motorboats, a growing store of empirical data has validated composite performance, especially in saltwater environments. Time - and increased sophistication and automation of production techniques - could well multiply the number of applications and the range of watercraft in which they prove practical.