Ferrocement for Boatbuilding[edit | edit source]
Ferrocement boats have been built and are now operating in, among other places, India, Ceylon, Uganda, Dahomey, New Guinea, Thailand, Samoa, New Caledonia, Fiji, Hong Kong, the Philippines, Cuba, Ecuador, the People's Republic of China, South Vietnam, Iran, Egypt, Brazil, and the Bahamas. This steady growth in application in developing countries constantly adds to our understanding of ferrocement's unusual properties and how this thin shell of highly reinforced cement can provide a surprisingly strong, yet simply fabricated boatbuilding material.
Boatbuilding applications of ferrocement can contribute to economic development and the general welfare of people in developing countries, particularly as quality timber suitable for boats becomes scarce because of housing and other demands from rapidly increasing populations. Moreover, quality timber often has a limited life: in tropical water teredos attack it, and in many coastal but arid regions (as the Red Sea region) the drying action of the sun seriously affects wooden craft pulled up on the beach. Accordingly, many boats last such a short time that owners are continually in debt-they cannot repay the initial loan before they need new loans to replace worn-out boats.
Of the two general types of ferrocement boatbuilding, one has been practiced in a good many countries around the world, and the other has found typical application in the People's Republic of China. The first involves western-style craft with hulls built with state-of-the-art technology for deep-water fishing or recreation. Often as complicated as other boatbuilding methods, this type of construction requires some skilled labor, is relatively expensive, and in developing countries is mainly suited to equipped shipyards. Experience with this approach goes back a decade. Typical examples are FAO projects in Thailand* and Uganda, UNIDO projects in Fiji, and the commercial construction of fishing vessels in Hong Kong. The panel recommends that developing countries enter ferrocement programs for such oceangoing ferrocement boats only with expert supervision, with extreme emphasis on quality control, and in a well-equipped boatyard. Under these conditions, craft can be made that contribute significantly to deep-water fisheries development.
FERROCEMENT FOR CRAFT OF LOCAL DESIGN
The second type of ferrocement application is the construction of simple, indigenous hulls designed for smooth-water use, such as the ferrocement sampans built by the thousands in the People's Republic of China. In Appendix A, these Chinese techniques are discussed, and photographs show clearly the unsophisticated conditions in which a rural commune produces fairly large and very satisfactory boats at a rate of about one per day. This experience demonstrates that unlike deep-water craft, these ferrocement boats can be built with confidence within the lesser standards attainable in rural areas of a nonindustrialized country.
Indigenous workboats (such as sampans, dugout canoes, chows, and the type of craft used on the Ganges, Nile, Zaire [Congo], and Mekong Rivers) with curved hulls 25-60 feet long are ideally suited to ferrocement's unique characteristics and take best advantage of them. Ferrocement derives great strength in curved shapes. The lack of design specifications-a worry of naval architects now working on deep-water vessels-is relatively unimportant for these craft. They require less stringent technology and quality control because they undergo far less stress and danger than deep-water vessels.
Indigenous boats are mainly hull, which allows ferrocement's cost savings to be maximized for the builder. (In a western-style boat internal fittings often account for a high percentage of costs; any saving on the hull is a small part of the total cost.) Indigenous-style boats are best built locally, by the usually available and low-cost labor supervised by a trained technician.
Indigenous craft are often unpowered, at least by an internal engine, so questions of adequate hull support for drive-shaft vibration (the lack of which caused one celebrated ferrocement failure in a developing country) are irrelevant. Yet, the boats can easily be powered externally, an important advantage where existing wooden boats are too frail to take power (as in the Ganges Delta).
Several panelists felt that the use of "long-tailed," powerpole, outboard engines should be explored in development programs for simple ferrocement hulls. Such engines are used by the thousands in Thailand because of their simplicity, lightness, and versatility.
Ferrocement, with its adaptability to curves, may improve local designs by allowing the corners required by the current plank construction to be smoothed out.
Weight is not a major factor in the displacement-type hulls of indigenous-styled boats, although they are often already so heavy that conversion to ferrocement may yield craft equivalent or lighter in weight.
BUILDING A FERROCEMENT BOAT
In industrialized countries many ferrocement boats are built in backyards far from water, but in developing countries building sites will probably be at the water's edge because of transportation difficulties. A waterfront location should be chosen with the size of craft, its draft, and its launching clearly in mind.
Although the site must be accessible for delivery of construction material, it can be located far from commercial harbors because needed equipment and tools are portable. Cement and wire mesh, as normally packed for shipping, seldom dictate choice of a site, but availability of sand may be important in areas where bulk transport is particularly difficult. Electricity may be desirable in some cases, but is not necessary. A shelter will be required to protect unused cement and improve working conditions in rainy areas. In river and coastal regions, where the need for boats may be very scattered, or in areas where flooding and terrain changes make a single building site less practical, the entire production facility could be located on a barge capable of moving to all sites, or of moving with fluctuating flood levels.
There are five fundamental steps in ferrocement boat construction:
- The shape is outlined by a framing system.
- Layers of wire mesh and reinforcing rod are laid over the framing system and tightly bound together.
- The mortar is plastered into the layers of mesh and rod.
- The structure is kept damp to cure.
- The framing system is removed (though sometimes it is designed to remain as an internal support).
Where scaffolding equipment is not readily available, the hull may be built in an inverted, or upside-down, position, resting on a suitable base (see Appendix A). There are several ways to form the shape of a boat. One can build a rough wooden boat first, or use an existing, perhaps derelict, boat. In another method, pipes or steel rods frame the shape of the hull. A third way is exemplified by the construction of Chinese sampans (described in Appendix A): a series of frames (welded steel in this case) and bulkheads (precast in ferrocement) are erected to shape the hull. Layers of mesh are then firmly bound to the frames, which are left in place to give rigidity to the final hull.
Recent methods for outlining the hull's shape include using thin strips of wood to which the mesh and rod are stapled and which remain inside the final concrete structure. Other innovations include plastering the outside of the hull first and finishing the inside a day or two later after the frames, or supports, have been removed.
BOAT SIZE
Ferrocement boats from 25 to 60 feet long have been built to operate successfully. Above and below this range, ferrocement has not yet been used long enough for the panel to class it markedly superior in all respects to alternative materials. Yet the need to build craft less than 25 feet long from cheaper and longer-lasting materials is great because many such small craft are used in developing countries. Most important for river use in certain countries, they often provide a major means of personal transport (in the Ganges Delta and Mekong Basin, for instance).
Some small craft have been built, and some U.S. university engineering schools have competed in ferrocement-canoe-building contests and races. These isolated examples suggest that further development work could make ferrocement boats in the less-than-25-foot range practical, as well as competitive with wood, fiberglass (FRP), and metal boats.
The panel believes that developing country laboratories interested in research into ferrocement application will find challenge in concentrating on methods to produce suitable small craft. Research is also needed at the other extreme, for hull lengths over 60 feet, but this job should not be tackled without adequate facilities.
QUALITY CONTROL
Ferrocement, like conventional boatbuilding materials such as steel, aluminum, or FRP, benefits by good specifications and quality control. At each step of assembly, careful inspection should ensure a product quality consistent with its expected use. Inspection procedures deal mainly with common-sense issues and are primarily visual.
In countries proposing to engage in significant ferrocement boatbuilding activities it would be desirable for appropriate laboratories to evaluate the basic raw materials at hand: cement, sand, and water-by district if necessary. Test panels should be made to determine their properties and to establish guidelines for appropriate mixes.
Ferrocement boatbuilding supervisors should maintain a continuing quality-control program. This vital factor is one potential source of weakness in the use of ferrocement for building deep-water vessels, since workmen in developing countries may have neither an understanding of, nor a concern for, specifications and quality control. It is to teach supervisors the principles of ferrocement quality control, among other things, that the training institutions suggested in Recommendation 8 are required.
When mortar is forced through the many layers of mesh used on a deep-water boat, it is difficult to ensure complete and uniform penetration. Some construction methods aggravate this difficulty more than others. Because of this problem, boats have been built with unsuspected air holes within the ferrocement; the resulting voids cause weak points in the hull, especially if water enters and corrodes the mesh. If necessary, hulls can be drilled to find voids and then grouted (filled with more mortar). Proper application technique and adequate quality control, however, will ensure that good mortar penetration takes place. A simple vibratory tool, such as an orbital sander, usually solves most of the problem. Corrosion seldom occurs if adequate mortar cover is maintained over the reinforcement.
However, as previously suggested, the degree to which these factors are important depends upon the expected use of the vessel.
CAUTIONS ON FERROCEMENT FOR DEEP-WATER CRAFT
The panel concentrated on simple craft for inland waterways of developing countries because in this situation current ferrocement technology can be utilized with confidence, despite the many differences of available skills, boat design, climate, etc., among countries. However, ferrocement boatbuilding in technically advanced countries has, so far, emphasized pleasure craft and trawlers designed for deep-water use, and the panel feels a responsibility to reiterate the warning to developing countries that more caution is needed when they consider ferrocement for these craft.
Ferrocement meets its ultimate test at sea: the stresses are large and unpredictable, and human lives are at stake. Boat design is not a precise science, and a pressing worldwide need exists for adequate structural-design information. This need applies to other materials, but ferrocement is less widely known or understood. Because its very nature requires combinations of constituent materials, quality control is important, but the development of ferrocement has been pushed forward largely by innovative amateurs who little understood the material and, sometimes, boat design. Only now is the engineering community beginning to investigate ferrocement as a boatbuilding material. Detailed specifications and standards are still at an early stage of formulation.
Successful ocean-going boats and marine structures can be built, and have been by the hundreds. Some ferrocement boats have survived extremely rough treatment, but there have also been striking failures. In developed countries, some commercial ferrocement boatbuilding ventures have been overpromoted and have gone into bankruptcy. The panel recommends that developing countries planning to construct ferrocement trawlers and other deep-water craft should exercise great care in selecting boat designs and ferrocement expertise at this time. They should carefully investigate any company proposing to establish local operations, inquiring into the number of boats it has built, and the professional background of the company's staff (see Recommendation 9).
Ferrocement's weakest feature, compared to wood or steel, in deep-water boats is its lessened resistance to penetration by a sharp object. This penetration is called "punching" to separate it from "impact" in which a broad surface area is struck and to which ferrocement is quite resistant. Small holes can be quickly repaired, but when punching is likely to be a serious problem, some sort of surface protection might be added, or the steel content of the ferrocement could be increased.
These cautions do not contradict earlier statements on the simplicity of ferrocement construction; they stress only that techniques of design and construction are new and that for deep-water boats they must meet very stringent requirements.
OTHER APPLICATIONS ON WATER
Ferrocement could be used in the construction of floating wharfs, which can be placed (or built) in any location, thus providing access to otherwise inaccessible coastal or river areas. Tugboats seem to be ideal craft for ferrocement construction because they are heavy and highly fendered. Barges are also important applications for ferrocement, particularly the ark-shaped lighters used widely in Southeast Asia, Africa, and Latin America. Flat-sided, flat-bottomed barges are less adaptable, but an apparently successful one is operating in Thailand, carrying cement on the Chao Phya River. Reinforced concrete barges (with reinforcing rods rather than mesh and with walls several inches thick) have been operating successfully for many years in Hawaii, the Philippines, and New Zealand.
Developing countries might also take advantage of their labor resources to construct high-quality, western-style, deep-water pleasure craft for export to North America and Europe.
Other structures on water are adaptable to ferrocement construction in developing countries. They are listed below to suggest the possibilities.
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Buoys |
Floating and submerged oil reservoirs |
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Docks, including floating dry docks |
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Floating breakwaters |
Offshore tanker terminals |
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Houseboats |
Floating bridges |
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Pontoons |
Floating shelters for suitable flood- prone areas (e.g., Bangladesh) |
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Submarine structures |
