No_11_November_1969 — Page 33

The first ferro cement vessel to be built in Hong Kong was launched last month. Built by the Hong Kong associates of a New Zealand Company that has pion- eered the development of con- crete boats, the 'Pak Tak' is of 62 tons and measures 54 ft. 6 in. overall.

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concrete launching

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HE was not the first to adapt rein- forced concrete techniques to marine craft building, but the name of Dr. Luigi Nervi, the Italian engineer, is probably the most widely known for his work in this field, which culminated in the sleek concrete yacht he built in the 1930's.

It was Nervi who developed ferro cement, though as far back as 1848 a French farmer named Joseph Louis Lambot had built a crude form of ferro cement boat. In post war years the construction of concrete boats has been carried out in several centres throughout the world. New Zealand has been very active; a number of concrete barges has been built in the Philippines; Thailand recently launch- ed a 52ft. ferro cement fishing vessel; and last month the world's largest ferro cement fishing boat was launch- ed in Hong Kong.

Ferro cement is not to be confused with the reinforced concrete used to build ships during the last two World Wars as there is little similarity be-

Wire rods and reinforcing mesh in place

tween these materials. The reinforced concrete ships were of thick concrete wall construction, extremely heavy, and consequently had very limited capacity and required a great deal of power to drive them. These ships had little to recommend them, other than the fact that they could readily be built at a time when steel was in short supply.

Strong and impermeable

Ferro cement consists of a steel rod and wire mesh matrix covered with mortar, with a number of additives, which gives the material its strength, durability and impermiability. It is possible to build fairly large vessels in ferro cement with a hull thickness of only 11⁄21⁄2 in., making it comparable in weight with steel and wooden vessels of similar size.

The strength of ferro cement can vary a great deal as it is determined by a large number of variable factors. This characteristic of ferro cement enables the builder to produce a material of a

given strength to meet the require- ments of a particular type and size of boat, from standard basic materials.

Complex shapes can be achieved with ferro cement, including reverse curves. In fact, for a given thickness and configuration it is stronger in a curved form than as a flat surface. Thus vessels may be built to their ultimate form, though a danger is that builders not possessing adequate technology can produce a fine-looking boat that does not have the required strength.

The use of ferro cement in boat building brings a number of advantages such as high fire resistance and a low thermal conductivity - approximately one sixth of that of steel. The material is unaffected by marine borers and should the boat suffer minor damage it is possible to carry out minor repairs on the spot by simply mixing cement, sand and water in the correct pro- portions and applying this to the damaged area. Repair work has been further simplified with the advent of

Far East BUILDER, November 1969

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