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FRP materials are widely used in shipbuilding in the USA, Japan, Europe and other developed countries. Since the first FRP boat was built in the USA back in 1946, such boats have become quite common all over the world – developing faster in fifty years than steel ships did over an entire century!
(Published on October-November 2005 – JEC Magazine #20)
BY LI HENGLEI, ZHANG BO, WANG YIQUN, TAISHAN FIBERGLASS INC.
Fibre-reinforced plastics (FRP) are now widely used in shipbuilding because of their ageing resistance. In countries such as the USA and Japan, FRPs have been used to make trawler-type boats for years. More than 70% of trawlers in Japan are made of FRP, and in Taiwan, over 60%. In the USA, however, development in FRP boats now is due to barges and other types of commercial boat.
In China, although FRPs were used in boat building as early as 1958, the development of these materials has been slow, despite their many advantages over wood. There are still some 900,000 wooden boats in China today. The government has taken some action to promote the development of FRPs in shipbuilding, however, and the shortage of wood resources should give FRPs a good chance. To maintain and renew old wooden boats would require 3,000,000 cubic metres of wood!
FRP boats vs. traditional boats
The rapid development of FRP boats can be explained by their many advantages. They can be one-piece moulded in a relatively easy and labour-saving process. They are lightweight, strong, highly corrosion resistant, and almost unaffected by electrolysis. They can save energy. They have good impact toughness, absorb energy, and are difficult to damage through collision or extreme pressure, and their strength and rigidity can even be boosted locally through the use of extra plies. The boats are also easy to repair, and their maintenance is inexpensive and fast. They are self-coloured, with no need for painting. No frame structure is required for the cabin, which increases the available space.
Finally, FRP hulls are far less susceptible to fouling. Japan recently developed a new type of high-speed yacht using FRPs. The boat has a distinct advantage in that the cabin will not sway at high speeds, even in ocean waves.
Comparative advantages of glass fibres
Because boats stay in water for a long time, the material used to build them – besides being appropriate for the building process – must offer good dynamics and good water-and corrosion- resistance. Most FRP boats are made of resin reinforced with glass fibre. The glass-fibre industry continues to develop very rapidly, with new products being launched continually. There are several types of glass fibre, as a function of alkali content. These include A-glass, C-glass, and E-glass. E-glass fibre has higher tensile strength and water resistance than C-glass fibre, so it is the most commonly used reinforcement in FRP boats.
Products used in shipbuilding
The main products used in shipbuilding are spray roving, chopped strand mat, E-glass knitted mat and nonwovens. Spray roving, used in spray-up moulding processes, is characterised by a consistent filament density, non-static properties and low fuzz. It is easy to chop, wet out and impregnate, and exhibits good strand distribution and excellent processability.
Chopped strand mat is made of chopped E-glass strands bound by a powder adhesive. It can be used in processes such as hand layup and continuous moulding. It exhibits consistent thickness and s t i ffness, and is also easy to wet out and impregnate. Its excellent processability makes it suitable for a variety of moulding and processing technologies, especially open moulding and close moulding. Finally, it exhibits excellent mechanical strength during the production of finished products.
E-glass knitted mat is made of chopped glass-fibre strands randomly dispersed and laid on a roving matrix, and then knitted together. It is suitable for compression moulding, pultrusion, GMT and RTM processes. It offers consistent thickness, low fuzz, easy wet-out, fast impregnation and excellent processability. It combines the axial properties of woven roving and the multidirectional properties of mat products.
Nonwovens are suitable for hand lay-up and offer consistent thickness, low fuzz, easy wet-out, fast impregnation, good processability and excellent mechanical strength during the production of finished products. Their properties are stable in wet environments.
Boat design is a comprehensive technology that covers many subsystems. Only the designer pays attention to each subsystem, treats it as whole, and harmonizes all the different parts so that the boat can be effective both functionally and economically. FRP materials have a low specific gravity, greater rigidity and a potential for functional integration and property shift. If the boat designer succeeds in leveraging the advantages of FRPs while avoiding their disadvantages, the design will make the most of FRP excellence.