Composite materials are those in which strengthening material like carbon fibers, fiberglass or aramid fibers are reinforced in a resin to make a much stronger material with improved material properties for different applications. They offer higher strength to weight ratio than traditional wood or steel material structures and can require less skill to generate a significant hull finish.
Composite materials have been used in the marine industry for a number of years. The more traditional applications for composites include gratings, ducts, shafts, piping, hull shells, etc for several decades. Wood and ferrocement are some of the other composites techniques that are still being used for marine applications.
Marine Composite Materials
Ferrocement is probably the earliest use of composites in the Marine industry, used for developing low-cost barges. A steel frame formed of reinforcing rod that is covered with chicken wire, is used as a 'template' to form the hull by pouring cement around the template. It is then plastered with ferrocement and then cured. Although it is an inexpensive composite, armature corrosion is a common problem under chemically aggressive marine conditions. However, there are still a number of ferro boats in use today.
Glass reinforced plastic
Glass fibers became available just after the development of polyester resins. Soon, glass reinforced plastic boats came into existence since the early 1950s and continue to be a significant composite construction technique in Marine applications today.
Wartime requirements led to the development of 'hot molded' and 'cold molded' boat building techniques based on laying thin wood veneers over a frame. On the other hand, high-performance, urea-based adhesives have also been widely developed for molding marine hulls and in aircraft manufacture to help speed up the production process and reduce dependency on Aluminum and steel.
Aramid fiber Composites
Aramid fibers are being widely used to strengthen sailing yacht structures like keel and bow sections. Also, Aramid Fiber composites also have improved shock absorption characteristics, perfect for ocean racing applications.
Carbon fibers are increasingly used for sailboats, furniture on super-yachts and high strength interior moldings as they offer vessel stability benefits and high performance with minimal weight. Carbon fiber is also seen as a trendy material, often substituted for not only superior material characteristics but the aesthetics component of the woven material.
Pros and Cons of Marine Composites
Some of the key benefits of marine composites include:
- Excellent strength to weight characteristics
- Corrosion resistance - adaptable for different applications
- Structures with complex shapes and geometry can be made relatively easily compared to traditional methods / materials
- Lower maintenance costs
- Ease of repair
- Enhanced stiffness
- Customizable flexibility
Marine composites also have significant drawbacks that are listed below:
- Often, lower impact resistance
- Some composites can have a lower heat tolerance
- Lower UV resistance - this can be extremely important in a marine environment
- Higher initial cost than some traditional materials
- Lower quasi-isotropic elastic modulus than steel and aluminum.
Marine Composite Applications - Examples
Carbon fiber reinforced epoxy composites are increasingly being used in the hull of boats covered with honeycomb or foam, in structural frames, keels, masts, poles and boom, and even in carbon winch drums and shafting. The use of composites can contribute to improved performance and minimize the risk of failure in extreme sailing conditions. Racing yachts employ advanced polymer composites more extensively than any other marine structures to save weight and improve durability.
Racing powerboats are now increasingly made of advanced and hybrid composites for high performance craft and safety. Fothergill Composites Inc., Bennington, has designed a safety cell cockpit from carbon and aramid fibers with aramid honeycomb core to protect the driver in all conditions, particularly in the event of a high speed crash. This structure is capable of withstanding a 100-foot drop test without any significant damage!
In recent years, considerable progress has been made in understanding the characteristic of composite materials and their tailored structures in the marine environment. Processing and production sectors also have received more attention resulting in the potential for the construction of complex, large assemblies capable of withstanding heavy loads. However, the key challenges involved in employing composites for marine applications include the need for optimization of capital expenditure and operating costs of boats, ships and other marine artefact's constructed using composites.
Materials science and composite technology are advancing rapidly, and new composites such as epoxy mixtures including the application of carbon nanotubes are becoming more popular with ever growing concern for high performance marine structures. Indeed, lightness, ease of production, durability and strength enable composites to play a vital role in marine applications.
As the Marine sector continues to look at improving efficiency and reducing overal costs, Composite materials will play a huge part in the future of Marine construction.
Sources and Further Reading