Application of glass fiber in shipbuilding

Glass reinforced plastics, GRP, are a form of fiber reinforced plastics, FRP, which were introduced for marine structural applications in the 1940's in the form of Navy personnel boats. Since that time fiberglass have found widespread acceptance for yachts and small boats such as fishing trawlers up to 34 m in length. Although the future of glass reinforced plastics for larger ship structures is very promising, economic factors, and to some degree, questions of durability, limit their applicability.

Reinforced plastics used for ship structures are composed of glass fibers embedded in unsaturated polyester resins. Fiberglass is a man-made fiber made of reinforced plastic materials consisting of glass fibers embedded in a woven material. It may be referred to as glass reinforced plastic (GRP) or fiberglass reinforced plastic (FRP). The terms are a bit confusing because glass fiber in and of itself is sometimes called fiberglass, so the fiberglass composite is usually called fiberglass reinforced plastic (FRP).

In the marine industry, fiberglass is used for all types of boats and yachts, surfboards, fishing dinghies, dock boxes and various other marine components. Glass fibers have many desirable properties, like high electrical insulation, low susceptibility to moisture and a variety of high mechanical properties. Properties of GRP that are particularly useful for marine service, and have led to their extensive use for small boats, are high strength-to-weight ratio combined with good resistance to deterioration upon prolonged exposure to sea water. Lower maintenance costs for GRP hulls compensate for their relatively high initial cost as compared with steel or wood.

Fiberglass composite refers to the fact it combines fiber (the reinforcement material (which in this case is glass) and resin (a matrix). There is also fiberglass laminate which is thin sheets of fiberglass used to sandwich a core material. The glass fiber can be woven into a fabric, flattened into a sheet, or randomly arranged.

Fiberglass cloth is a woven material that is exactly what it sounds like. Think of woven material used in clothes, and like clothing material, there are a variety of weave patterns and fiber weights which influence stiffness. The cloth is made with continuous thin strands and weighs anywhere from 4-15 ounces per square yard. Heavier weaves, called roving, are made with untwisted fiber yarns, and can weigh as much as 48 ounces woven roving or more per square yard.
There are different types of fibers and fiber arrangements used in boat construction and for marine fiberglass repairs. Fiberglass woven roving is usually used in boat construction, fiberglass plain cloth is usually for marine fiberglass repairs.

Fiberglass mat - (or chopped-strand mat) is made of E-glass, with very short (2-3 inch) fibers placed randomly. The fibers are held together with a resin soluble binder, but this type of cloth requires a lot of resin. It’s relatively waterproof and can be sanded smooth. Mat is used mostly for getting thickness in fiberglass layups.

Of course, there are other options. They include unidirectional fibers (fibers run in one direction and are held together by a low number of single fibers); bi-axial fibers (layers of unidirectional cloth); tri-axial fibers (fibers are oriented in three directions); and veil mats (continuous strand fibers looped randomly).

Future of Boat Construction

The industry discussion is on whether boats will eventually be mostly manufactured with all-carbon fiber cloth as opposed to traditional fiberglass. The reason is simple – carbon fiber weighs less, adding maneuverability and improved gas economy, plus it’s stronger than fiberglass. It’s five times stronger but lighter than steel.
Carbon fiber is a polymer made with strong, thin crystalline filaments of carbon. Carbon fiber replaces the glass strands in fiberglass. Right now, it takes large, high-energy use equipment hours to heat the carbon atoms to the point where they produce the carbon filaments that strengthen the material.

You may be familiar with carbon fiber in non-marine products like golf club shafts, tennis racket frames and bicycle frames. It’s used in fighter jets, body armor, wind turbine blades, medical equipment, prosthetics, household furniture and iPhone cases. Is carbon fiber in most boat construction next?
Holding back greater use of carbon fiber is the cost which is approximately five times that of fiberglass. Another drawback at this point is that carbon fiber is more rigid which could impact the ride, plus more rigid materials are more prone to severe damage when hitting something (hopefully not another boat!). Some manufacturers are currently using fiberglass for boat construction and using carbon fiber in components like radar arches and hardtops.

The future of carbon fiber in boat manufacturing remains to be seen, but it’s something to be aware of. When the boat dealer or broker proudly mentions state-of-the-art “carbon fiber”, you can nod your head intelligently and ask how much that added to the price.

#fiberglass #shipbuilding #GRP