Ferrocement Applications in Developing Countries/10
Ferrocement Applications in Developing Countries (BOSTID, 1973, 89 p.)[edit | edit source]
Appendix A[edit | edit source]
Ferrocement Boatbuilding in a Chinese Commune
The eight photographs herein of ferrocement boatbuilding in a commune in the People's Republic of China are the first such to be published in the West. They show a large boatbuilding program in which simple ferrocement craft are produced With unsophisticated techniques in a rural area of a developing country. The photographs were taken by Anne Keatley, of the National Academy of Sciences, who visited the People's Republic in June, 1971.
The following text includes a report by Robert Keatley, a journalist who observed the site in 1971, and an analysis by the NAS panel of a total of 26 photographs.
First, the journalist's account:
A drive from Shanghai through the nearby countryside quickly shows a visitor why small boat construction is an important activity there. The rich land is flat, nearly marshy; dry surface is so scarce that peasants use asphalt roads for drying their grain harvests-it may slow traffic, but the land itself remains too wet.
But such roads are scarce in coastal China, a land cries-crossed by rivers and canals. Thus, historically, the sampan has filled the transportation role occupied in northern China by the horse cart.
Horse Bridge People's Commune is probably more advanced economically than its neighbors; it is often singled out as a place to take foreign visitors. Yet it remains a poor place. Its 36,000 people [arm an area of only 8,000 acres, including a maze of canals and rivers, and the space alloted for buildings; and the 7 percent total given over to private plots. Its vehicle assets comprise little more than a few tractors and eight rubber-tired carts. The boat retains its importance as a means of moving goods within the commune, and outside it.
Horse Bridge Commune has more than so workers assigned to ferrocement boat construction, and they average more than one completion daily. The factory is a sideline for the commune; it produces boats according to a plan worked out by the county and sells its output to the county, which resells them to users elsewhere in the region.
The most common sizes are 12-meter boats with 6-ton cargo capacity, and 15-meter boats with 10-ton capacity. Construction began in 1964. Recently, the factory has produced a 60-ton capacity boat and plans to try installing a d*sel engine. The smaller ones are towed or poled along the still canals. Open cargo holds for carrying night soil are standard features of most, if not all, boats.
The commune sells its 6-ton boats for 750 yuan (us 5330) and charges 1,700 yuan (us ) for the 10-ton size. It claims to realize a 7 percent profit for the commune.
Workers cite "ten superiorities" over wooden sampans, including longer life and cheaper maintenance. They claim a wooden sampan will last 20-30 years with good care; they don't know yet how long a concrete boat will last. The amount of material needed is not great; a 6-ton capacity boat needs 800 kilos of concrete and has a total weight of something over 2 tons.
DISCUSSION OF PHOTOGRAPHS
The main design change in converting wooden sampans to ferrocement boats was to make the bilge more rounded. The flat bottom and flat deck are retained, but there seems to be a slightly greater depth of hull to give more cargo space.
The boats are divided into six compartments, but only the three center compartments are used for cargo. The foremost compartment is used as living quarters for the crew of four men, who enter it through a deck hatch. The fifth and sixth compartments are living quarters for the owner and his family and are covered by an awning for shade and shelter. The vessels are propelled by sail and two yulohs (sculling oars). The stern yuloh (starboard side) is used in the conventional manner; the other, positioned over the forward bow (port side), is used also as a sweep.
Ferrocement is used to the fullest extent throughout, but wooden gunwales are used to absorb shock. The boats have a normal rudder attachment-a wooden gudgeon block bolt-fastened to the hull itself. The rudder is of a simple drop type that can be raised or lowered depending on the depth of water.
Before the Second World War, it was reported that suck vessels made approximately two trips per month, carrying night soil for fertilizer far into the countryside from the Shanghai area and often returning with vegetables for the local markets. Ferrocement boats are reported to cost only 50 percent as much as the wooden boats they replace and to have added stability and speed, apparently due to the improved hull shape allowed by the conversion from wood to ferrocement.
Although only one hull design is used (for the sake of economy), bulkheads are placed in any of several positions so that compartments can be constructed to hold different cargoes.
The pictures indicate an extremely interesting boatbuilding operation. In a modern building, the vessels are built upside down over a pit from which the inside of the hull can be plastered. Inside the building are several areas where bulkheads, afterdecks, and foredecks are assembled alone or in combination as subunits of the final boat. These subunits seem to be built in quantity and then used on any of several hulls.
When hull-building starts, high-tensile wires are positioned along what will become the turn of the bilge and the centerlines of the hull; they are held taut with a Spanish windlass and pass over temporary wooden spells (crosspieces which will hold in place bulkheads and frames of the hull to come). Next, the precast concrete (or welded steel) bulkheads and frames are positioned and attached to the high-tensile wires which hold them upright. The "new moon" shaped frames are spaced approximately 1 meter apart; they are approximately 1 inch thick, 2 inches wide at the ends (deck level), and 6 inches wide at the center (keel level). Once in place, the bulkheads and frames outline the hull and provide shape and support for mesh and mortar that, when added later, form the watertight skin of the hull.
Inside the precast-concrete bulkheads are reinforcing rods extending out beyond the concrete. The layers of wire mesh for the skin of the hull are maneuvered down over this protruding reinforcing until they are snug on the bulkhead itself. The bulkhead reinforcing rods are then bent over and laid alongside the hull's reinforcing, and the layers of mesh are firmly fastened to them both.
Three layers of wire mesh are used, and between the innermost layer and the outer two are placed reinforcing rods that run the length of the hull. Extra layers of mesh are placed at potential stress areas, e.g., along the curve of the bilge. The first layers are placed transversely across the hull; later ones are laid along the hull's length.
The photographs show women wiring together the layers of wire mesh. They work from the outside only and have no helper on the inside. Apparently, they use a hooking tool 5 or 6 inches long to maneuver the tie-wire in and out through the layers of mesh. This is an improved technique compared to methods used elsewhere. The wire in the hulls is stretched very tight; some parts are prewelded or precast, but there appears to be no welding during construction.
The wire mesh (square rather than hexagonal chicken wire) is irregular, with varying distances between the strands. Close inspection of the photographs indicates that the mesh itself is probably woven from single-strand wire in the commune (or at a nearby location). The ends of the mesh appear to have been looped and are not square, further suggesting that they are handwoven.
The longitudinal reinforcing rods appear to be about 1/4 inch in diameter, are spaced approximately 3 inches apart, and are securely fastened to the mesh. Apparently, there is no other longitudinal stiffening.
ORGANIZATION OF THE BUILDING SITE
An analysis of 26 photographs suggests that 9 or probably 10 boats are being built and cured simultaneously. If the ferrocement is allowed to cure for 14 days, 2 boats could be built per day, yielding 18 to 20 boats per month. It is possible to shorten the curing time on land to 5 or 6 days if the remaining cure is done under water. Though the photographs show no positive evidence, it appears quite probable that this is done.
No pictures show the actual plastering operation; however, one freshly plastered hull and two being cured are visible. Curing is done by draping wetted fiber mats (hessian or burlap) over the hull. A sprinkler system may be used to cure the interior surfaces.
The boats are launched upside down, either to be rolled over in the water or to right themselves by their buoyancy, perhaps after final curing by immersion in the water. A crane with a boom about 10 meters long is used to launch the boats. The vessels are moved from the construction shed to the canal bank on a cradle that runs on tracks. The cradle is placed under the boats easily, without need for a crane, because it can be run under the hull and accurately placed by the people working in the pit over which the boats are built. Tracks run from each building bay through a set of railroad points to the canal bank next to the launching crane. The cradle consists of two dollies approximately 1.5 meters long, each having four wheels. The dollies are placed approximately one third of the vessel's length from either end. Once in place, the boat is rolled to the canal bank, apparently by manpower alone.
The mortar-mixing shed is roofed but has open sides and is located adjacent to the main construction building. Water is piped to a standard faucet, and there is a large area for premixing the concrete. A horizontal-type rotary concrete mixer is visible.
The building and organization are well engineered and produce what is probably a combination (with improvements) of different types of vessels previously built by individual families. An ever increasing demand to expand the fleet of small boats to cope with population increase may have made it mandatory to devise rapid boatbuilding techniques. Possibly, too, a natural depletion of good boatbuilding timber and the allocation of any available steel to other purposes led to the use of ferrocement.
The lesson to be learned from these photographs is that with proper engineering, mass production in ferrocement is not only feasible, but practical. Standardization of design appears important.
These methods of construction indicate a considerable amount of planning and engineering skill. Precasting sections of ferrocement hulls is a significant advance in construction techniques, one that makes mass production possible. It also suggests new design considerations and new lines for basic research into ferrocement science. In most parts of the world there is considerable controversy over the method to be used to provide support and shape for the layers of wire mesh. Temporary wooden and water-pipe supports are generally used, but both suffer drawbacks, particularly during their removal after the hull is mortared. The Chinese, in contrast, provide support and shape the mesh with precast concrete bulkheads or frames that end up as integral parts of the boats. Furthermore, these precast frames and bulkheads are the key to producing uniformly shaped vessels so that standardized sheets of mesh and fittings can be employed, with resulting economies from building boats of interchangeable parts on a "production line" basis.
Much can be learned, too, from the methods the Chinese use at their urban boatbuilding factories. Photographs of the Wusih ferrocement boat factory published some years ago show 20 hulls under construction inside a modern building.* They also show an even greater refinement in subassembly than in the commune, for all subassembly is done on one side of the building, and the overall construction and plastering on the other. Both steam and air curing operations take place in the same building.
The need for a large number of new hulls forced the Chinese to seek mass-production techniques. Ferrocement has allowed them to do this.