How Well Do You Know Composites?



How well do you know composites?

Until the late 1940s, nearly all recreational boats were built of wood. Without careful and continuous maintenance, those boats tended to leak, rot and fall apart. In the 1930s scientists at Owens Corning invented fiberglass as an insulation material, but it wasn’t until after World War II that innovative manufacturers decided to apply this material to boat building. By properly layering and laminating glass fibers with resin, they were able construct hulls, decks and components.

Early fiberglass boats had some issues, mostly having to do with the resins builders used, but by the late 1950s better resins were developed, and boat quality improved. Materials and processes have been improving ever since, and for many reasons composites continue to be the most prevalent material used in recreational boats today.

Mark Richards, CEO of Grand Banks/Palm Beach, says using carbon fiber eliminates up to five tons of weight in some models, which translates to better speed and performance.



Composite Advantages

How well do you know Composites?Composite boats have good strength-to-weight ratios and durability, although they can crack, so hull bottoms and striking surfaces are often reinforced. They can be finished to a high quality using either gelcoat or paint, and fiberglass can be molded into complex shapes, including curves. Recreational boat builders love fiberglass because it is built in a mold; it is repeatable, so sequential boats are effectively the same, which is important for class racing sailboats. But the repeatability also means builders can produce boats in series more easily and cheaply. Fiberglass revolutionized production boat building by providing a cost-effective way to construct hundreds of similar boats.

Early production boats such as the 1962 Pearson Triton I grew up sailing were overbuilt. When my father and I replaced a throughhull, we noted that the hull was nearly 2 inches thick. Back then fiberglass builders weren’t confident in the strength of the material, so they used a lot of it, but time has changed that. Ultra-thick solid-glass hulls made boats heavy, and that worked for a narrow-beam sailboat with a weighted keel, but heavier hulls decrease efficiency, especially in powerboats.

Advancements in techniques and materials have vastly improved composite boats over time. Modern materials and techniques — coring, carbon fiber, vinylester resins, epoxy — and advanced processes such as resin infusion and vacuum bagging were all developed to increase strength and save weight.

Composite boats are built using fibers that are impregnated with resin. When they harden, the fibers create complex shapes such as hulls, decks, hatches, hardtops and more. Different types of fibers can be used, as can different types of resins. Builders can add coring material, too, which reduces weight and noise and adds strength.

How Well Do You Know Composites

The materials used and the way they are put together vary greatly depending on the builder. A basic fiberglass boat has an outer skin (gelcoat, typically) on one side, and then progressive layers of glass fibers impregnated with resin complete the laminate structure. Traditionally builders used polyester resins and a combination of glass matt (omnidirectional), woven glass (stronger bi- or multiaxial fibers) and sometimes chopped glass fibers. Some builders use a chopper gun to spray in strands and resin. Hand-laid fiberglass is a laminate where the glass is carefully placed by hand, covered with resin and pressured with a roller to squeeze out any air bubbles and eliminate voids.

Carbon fiber is used extensively on Palm Beach GT series boats, including on the dash as shown here.

Carbon fiber is used extensively on Palm Beach GT series boats, including on the dash as shown here.

Carbon Fiber

Raw carbon fiber can be identified by its gray-black strands that are often woven into roving. This material is created by bonding carbon atoms together so the crystalline structure aligns and creates long, thin fibers that are then bundled together to create fabric. Carbon fibers have many advantages:

  • They are stiff
  • They are lightweight
  • They tolerate high temperatures
  • They are resistant to chemicals
  • They don’t expand or contract thermally.
  • When laminated into a structure with resin, carbon fiber composites have a very high strength-to-weight ratio and are extremely rigid, though they are somewhat brittle. Carbon fiber is an excellent boatbuilding material, especially when weight reduction is a priority, and can be used in place of traditional glass fibers and bonded with different resins. Carbon fiber’s primary drawback for use in building recreational boats is cost. Some builders I spoke to did not feel the benefits were worth the price. They said that without carbon fiber they could build adequately strong, lightweight composite structures.

Because it is expensive, carbon fiber was once reserved for specialized parts, such as the masts of racing sailboats or cantilevering decks on megayachts, and for constructing hightech boats such as America’s Cup race boats. The cost of carbon fiber has been decreasing, which has led some recreational builders to expand their use of it.

Using carbon fiber aloft reduces a vessel’s weight and lowers its center of gravity

Using carbon fiber aloft reduces a vessel’s weight and lowers its center of gravity

Builders Who Like Carbon Fiber

Sister companies Palm Beach and Grand Banks continue to build their hulls using vacuum-infused E-glass with core-cell foam and vinylester resins, but they use carbon fiber broadly above the hull. Palm Beach GT series boats use carbon fiber extensively in the deck and superstructure. The jack shafts between the engines and IPS pods are carbon fiber, as are the dashboard, the sink and even the bowl of the marine head. The use of carbon fiber is being expanded in all the Grand Banks and Palm Beach models.

Wooden Hull

Other builders may write off the use of carbon fiber as marketing hype, but Mark Richards, the founder of Palm Beach and current CEO of Grand Banks/Palm Beach, stands by the company’s advanced construction. According to Richards, using carbon fiber aloft reduces a vessel’s weight and lowers its center of gravity, maximizing the performance of the builder’s signature warped hull form, which has a narrow entry to slice through waves and flares aft to keep weight balanced amidships. Richards said carbon fiber and coring materials eliminate up to five tons of weight in some models, which translates to better speed and performance. He added that the builder’s hull form would not run correctly if the boats were heavier.

The Palm Beach GT50 can reach a top speed faster than 40 knots. The Grand Banks 60, a large and comfortable cruiser with three staterooms and a lot of amenities, can surpass 30 knots and maintain a range of more than 500 nautical miles even at a fast cruise. Richards feels the expense of carbon fiber is warranted because of the weight savings and efficiency that is gained.

Swedish builder Delta Powerboats also uses carbon fi ber throughout its vessels, including the hull. Delta principals tout the benefi ts of carbon fi ber’s superior strength-to-weight ratio. The builder uses resin infusion, a process whereby laminate components are carefully laid out and sealed with a vacuum bag. A precise amount of resin is then pulled through the laminate, which helps maintain the resinto- fabric ratio and eliminates voids.

Tell the Difference
DESPITE THEIR SIMILAR APPEARANCE, different resins — polyester, vinylester, epoxy — have different properties.
Polyester resin is a good boatbuilding material but has some inherent drawbacks. Polyester continues to bond with water throughout its life, which means boat hulls gain weight and lose strength over time and are subject to blistering. The interaction can be inhibited by barrier coatings, but it is not ideal. Vinylester resin, a step up, is polyester resin enhanced with epoxy, thereby eliminating many problems associated with polyester. Vinylester resins are water resistant and have their strengths. Their cost falls between polyester and epoxy, and their lower resin viscosity aids vacuum infusion. Polyester and vinylester resins cure differently depending on temperature. Since most boatbuilding shops are not temperature controlled, builders must carefully adjust MEKP catalyst levels to account for temperature or else the laminate will not fully cure. Epoxies, on the other hand, if properly mixed are not temperature dependent and can also be post-cured to ensure full hardness. Epoxy has stronger adhesion properties, which can help keep structures from delaminating, especially around a core. Polyester is half the cost of vinylester, which is half the cost of epoxy.

Going Further

The processes Palm Beach and Delta are using deliver high-quality lightweight laminates using carbon fi ber. Their construction techniques are at the forefront of recreational boat building, but further steps can be taken when even lighter parts are needed. They just aren’t cost effective for building pleasureboats, yet, because the construction costs are higher and the gains to a recreational boater are minimal.

Some high-tech racing boats and composite aircraft such as the Boeing 787 Dreamliner use prepreg carbon fi ber construction. This process pre-impregnates the carbon fi ber strands or tapes with a precise amount of resin, typically epoxy. Boeing uses robotic equipment to precisely lay down epoxy-impregnated carbon fi ber. Once the structure has solidifi ed, it is post-cured in an industrial oven/autoclave, which Epoxy Over Wood Hulladds heat and pressure. Prepreg carbon fi ber laminates are extremely lightweight and incredibly strong.

Advanced composites in aircraft not only save weight, which makes planes more fuel effi cient, but they have other advantages. Composites require less maintenance than traditional aluminum airframes. They can be pressurized better, too, because air doesn’t leak through rivet holes, and the planes can be humidifi ed inside without risking corrosion. It all makes for a better passenger experience. So why don’t recreational boat builders prepreg their boats? It simply costs too much. It may be worth it on a $250 million airplane, but the equipment and additional cost don’t make sense for most boats and boat buyers.

Advanced construction materials such as epoxy resins, carbon fiber, foam coring, vacuum bagging and resin infusion all help builders create lighter and stronger boats.

Epoxy Boat Building

Boat builders such as Vicem and Jarrett Bay Boatworks use “cold molding,” which is a technique where an underlying wood structure is covered by epoxy. Boats built in this manner are very strong, because the wood acts as the structure and the epoxy fully bonds and seals the wood from any interaction with water. Some fi shermen like the ride, feel and sound cold-molded boats make as they move through the water, and think this helps them catch more fish.

Epoxy Over Wood Hull

Epoxy Over Wood Hull

MJM Yachts produces Downeast-style cruisers and creates composites with extensive use of closed-cell coring, multiaxial glass fi bers and epoxy resin. MJM uses “wet-preg” E-glass that is soaked in a resin bath of epoxy, drawn through the rollers of an impregnating machine and carefully laid out in the mold. Epoxy is very strong and adhesive, so MJM does not need to use chop strand mats between the layers. Long, continuous fi bers save weight and add strength. Vacuum bagging then compresses the structure further, eliminating any voids. Parts are built in large insulated industrial oven rooms. Once the laminate structure of the hull, decks and other parts of the boat are complete, the rooms are sealed and become computer-controlled convection ovens that allow parts to post-cure at 150 degrees for 12 hours. All laminated parts are cored composites, which gives them the panel stiffness and strength needed to meet ISO engineering requirements without the weight.

Hulls are cored below the waterline with styrene acrylic- nitrile (SAN) foam that is lighter, stronger and tougher than other foams, so it can hold up to the high-impact loads of running fast through waves. The centerline is solid glass so it can withstand grounding and blocking during transportation. For added safety, MJM boats have a watert ight collision bulkhead in the lower stem that creates an enclosed foam core–fi lled fl otation compartment.

Advanced construction techniques and modern materials such as epoxy resins, carbon fi ber, closed-cell foam coring, vacuum bagging and resin infusion all help builders create lighter and stronger boats. Using superior materials and processes costs more but creates boats that are faster and more fuel effi cient. Many composite boats have an outward appearance similar to fi berglass, but the technology, materials and methods used to build them give them unique characteristics of performance and durability.