by A. KOROLEFF, Director, Woodlands Research Division, Pulp and Paper Research Institute of Canada, Montreal
Since the war, through the work of FAO and undertakings such as the Point Four Program (United States), the Colombo Plan (Commonwealth) and others, organized endeavors to develop or improve logging operations by the introduction of better methods and equipment have been greatly intensified in many underdeveloped countries. In some already industrialized countries a similar trend is evident in the widespread demand for more efficient logging methods. Rising labor costs are emphasizing the importance of logging mechanization.
However, there seems to be a lack of clear cut data-in print at least-on the principles that should guide organized improvement of logging, and particularly the choice and transplantation from one country to another of certain locally well-proved logging practices. Although certain logging methods are, even intrinsically, more efficient than others, what is sound under one set of conditions may be quite impractical elsewhere. Those who determine which logging methods can be profitably transplanted from one country to another are dealing not merely with the techniques and economics of forest harvesting but are exerting a much deeper and more lasting influence.
A sound logging practice should meet at least the following requirements: it should make efficient use of the most appropriate power source, and it should be consistent with forest management objectives. 1
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In a broad sense - including the needs of forest labor management and such important forest influences as soil and water conservation.
Sources of power for logging
The three main sources of power for logging are:
a) human and animal power;
b) machinery (operated on solid or, usually, liquid fuel 2);
c) the harnessed force of gravity.2 In nearly all countries where logging has been partly mechanized, the dependence on liquid fuel appears to be very great, whereas the use of wood as fuel for logging machinery is limited and continues to decline. Only in the U.S.S.R. has the reverse trend been noted in recent years. The policy there is to operate logging machinery chiefly by electricity produced from unmerchantable wood, including slash, via producer gas or, less frequently, steam.
In most underdeveloped countries the first source is likely to be cheap on a per hour basis, but the cost per unit of wood produced may be comparatively high, as the efficiency of native logging practices is frequently low, and an adequate labor force may or may not be available in the timber areas to be logged. Obviously, a substantial increase in productivity, without a corresponding rise in labor costs which would largely offset that gain, is desirable. But to achieve this requires careful study, competent leadership, conscientious and patient work toward that objective, and considerable time.
The managements of timber enterprises having ample capital, particularly those possessing this advantage in little-developed countries, tend to act quickly to introduce logging machinery that is efficient, if conditions are suitable. This machinery-principally of American make or type-is always dependent on liquid fuel. Its efficient operation necessitates competent supervision, skilled labor, adequate maintenance provisions and delivery of liquid fuel, often imported, to the machine in the forest. In many cases all this is so well justified that the endeavor is a success, notwithstanding the expense and problems of adjustment. This applies especially to large-scale, concentrated operations in valuable timber. However, frequently the underdeveloped countries simply cannot afford the machinery and the liquid fuel, or the machinery may not fit in with the physical conditions or the overall economy of the country. Even in the United States there is a feeling that some of the present-day logging machinery, which is geared primarily to large-scale, concentrated forest operations, is too costly. There seems to be a need, therefore, to develop equipment and efficient techniques which will meet the requirements and the modest means of small wood producers. It is claimed that decentralized logging often offers considerable advantages in lower overhead, economic stability and perhaps conservation.
The force of gravity is an excellent and freely available power source for logging if it can be suitably harnessed, either on land or water. River driving, frequently a very cheap means of transporting wood over great distances, has in the past played an important part in the economy of many countries, and still does in many places. In a number of underdeveloped timber countries, efficient river driving is yet to be introduced. It must be remembered, however, that the low floatability of some species is unfavorable. The use of logging flumes and gravity chutes, which was never very great, has apparently been declining. Gravity cableways have made as yet only a limited contribution in the field of mountain logging, notwithstanding the variety of types available. They are often lacking in mobility, and are rather costly. Yet, among possible power sources for logging in rough terrain, the force of gravity still remains largely unharnessed.
Figure 1. - Wire skidding set-up for the transport of wood
How efficiency may be increased
Improvement in the efficiency of logging methods may come about as a result of:
1. better planning and supervision, time and motion studies, labor training and other means of eliminating waste of effort, improved tools, etc. - without any fundamental change in method;2. adoption and judicious adaptation of the more efficient techniques and equipment developed elsewhere;
3. systematic research leading to the development of new methods entirely suitable to local conditions and complying with the requirements of sound logging practice.
This last approach seems to be the one least used. Unless a logging technique is, so to speak, made to order, it is not likely to meet all the essential requirements. On the other hand, the development of technique on a soundly pre-selected, specified basis is usually far from easy. However, it should be undertaken in an effort to find a substitute for primitive logging practices which are fundamentally unsound.
Practically all over the world the conventional way to bring wood down steep, rough slopes is essentially unsound from the point of view of power source, efficiency and conservation requirements. The prevalent practice is for a teamster and a draft animal to struggle up, then down, the hill for each load, with much zigzagging. Where the ground is too steep or too rough for the animal, the customary procedure is either to move the wood manually with the aid of gravity, however strenuous the effort, or to abandon it as inaccessible. 3
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The use of chutes, gravity inclines and cableways is rare, because they require comparatively large concentrations of wood to justify the considerable investment involved.
The logical solution of this problem is to arrange one-way transport by gravity, with the wood moving down, clear of the ground, over a suspended wire or wire cable. To warrant wide use, such a system should be cheap, simple, efficient and highly mobile. Over a long period of time and in many different places, attempts have been made to move wood or other materials from steep slopes, or from the ground above them, by gravity over a suspended cable. This principle is employed in some commercial cableways and is used by some farmers in mountainous countries, such as Norway and Switzerland, for transporting their produce into deep valleys. But loggers have as yet profited very little from such cableways, because most of the existing arrangements lack both flexibility and mobility.
The principle of wire skidding
Wire skidding is the term introduced in eastern Canada by the writer several years ago when work was started to develop a technique for transporting pulpwood down steep slopes over a suspended wire. Periodic experimenting and design was carried out by the Pulp and Paper Research Institute of Canada in co-operation with several paper companies, and the Institute's wire skidding method is now being adapted to several commercial operations. 4
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A full description of the method is given in the bulletin Wire Skidding - Wood Transportation by Gravity over a Suspended Wire, by A. Koroleff and R. D. Collier, Pulp and Paper Research Institute of Canada, Montreal, 1954.
As shown in the illustration, a wire is suspended between a tree or a stump on the mountain and another at the bottom. This single-strand, steel wire, only slightly thicker than a match, is quite inexpensive but very strong. 5 The overall grade between the terminals 6 can be from approximately 25 to 60 percent; and the wire span may be up to at least 1,500 feet (460 m.). Surprising as it may seem, this thin wire can carry loads of one-quarter or even one-third of a ton- that is, up to about 15 cubic feet (½ m³) of pulpwood - at a speed of 50 miles (80 km.) per hour. For still greater loads, thicker and correspondingly stronger wire should be used. A load is suspended from the wire by a small, slotted hardwood block, about 1½ x 2 x 3 or 4 inches (3.8 x 5 x 7.6 or 10 cm.), and by slings of thin wire, 0.07 - 0.1 inches (0.18 -0.25 cm.). Being very cheap, the load carriers and wire slings are expendable. 7
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Gauge 8 (0.16 in. or 0.4 cm.) wire, priced at about 1 or 1½ cents a foot (3 or 5 cents per m.) has a breaking strength of well over two tons. Its weight per 1,000 ft. is only 68 lb. (10 kg. per 100 m.).
6 Declination of a straight line between them.
7 When used only once, the load attachments cost about U.S. $0.50 per 100 cubic feet (2¾ m³) of wood transported.
So far, this method has been used chiefly with four-foot (1.2 m.) pulpwood bolts, the individual bolts being up to 30 inches (76 cm.), but mostly under 10 inches (25 cm.) in diameter. When bolts are small, a load consists of several: when large, it may consist of only one or two bolts. However, a limited experience with 8 foot (2.4 m.) bolts and with 12 foot (3.7 m.) logs, up to 15 inches (38 cm.) in diameter, suggests that these can be wire skidded at least as efficiently as short bolts.
Two men, working fairly steadily but not strenuously with wood brought close to the launching point, can usually send down the wire about 1,000 cubic feet (28 m³). Of wood per 8 hour day. This output rate allows for the initial installation of the wire and the moving and re-rigging of it at a new location from time to time. A two-man crew can usually rig the wire across a span of a quarter of a mile (0.4 km.) in less than half a day. It makes little difference in operating the wire whether the span is short or long. Once launched, the load travels automatically. To launch the load, either the wire is raised slightly at the back until it takes off, or the load is lowered off the supporting skids. A semi-automatic launching which takes advantage of the load's own weight is also possible. On reaching the lower terminal-usually within 30 seconds-the wood is discharged automatically by the force of its impact with the tail tree; yet breakage has been negligible, in the Institute's experience. If the wood is to be landed into a stream rather than at a roadside, this is easily accomplished by means of a load interceptor. This device may be simply an old tyre hung over the wire above the water and guyed to a tree.
The greatest part of the work consists of making up and launching the loads: gravity does all the rest. Medium-sized loads of pulpwood (several bolts, totalling as much as 6-7 cubic feet, or approximately 1/5 m³) can usually be made and launched by two men at a rate of one or two per minute. When the wood is small, wire skidding may even be operated by a single worker.
In addition to the main wire and the expendable load attachments, the equipment consists of a hand-operated wire tightener and a grip which serves to attach the wire to the tightener, permitting any extra length of wire to be left coiled. For a quarter-mile span, the whole set costs $100-$150. The wire is quite durable except when it is kinked through carelessness. 8
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Not only is single-strand wire much cheaper than a wire cable of the same breaking strength, but for wire skidding it is decidedly preferable to a cable in several other respects.
The ground profile under the wire matters only insofar as the overall grade of the suspended wire and the assurance of a sufficient ground clearance for wood loads are concerned. Since the wood travels over the wire entirely through the air, often higher than the tree tops, it is immaterial how rough and steep the slope is; it may even be a precipice. However, the wood launching points, whether near the mountain top or on the slope, should be chosen so that the ground drops steeply immediately below them.
While as yet only single-span wire skidding has been developed by the Institute and the co-operating companies to the stage of commercial practicability, some preliminary work has also been conducted on a multiple-span, continuous-wire system, with intermediate supports which permit changes in both the gradient and direction of the wire and also allow extension of the range. 9 Study of this technique is to be continued.
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Tandem use of several independent wire spans may be practical in some oases; but it requires rehandling of the wood at the junctions.
Although wire skidding is a new technique, it works effectively and may be considered as a highly mobile, simple and economical means of transporting wood down steep, rough slopes. There can hardly be any question about the suitability of the principal power source in wire skidding and about the compatibility of this technique with conservation needs. While common practice in the logging of steep slopes tends to clash with the fundamental principles of sound logging-efficient use of appropriate power, and consistency with forest management objectives - wire skidding conforms with these principles.
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