engleski

Choosing and Application of Forest Soft Machines

The paper deals with some experience in choosing and application of forest means of labour during the transitional period in a little country such as Croatia. Market economy oriented transition meets a number of both objective and subjective obstacles aggravating the definition of strategies in choosing and application of forest soft machines, particularly at skidding and silvicultural operations. The organisation of Croatian forests within one public enterprise, the owner of approximately 80% of all national forests, enabled it to create its own system of evaluating the most suitable equipment for forest work. The attempt to define logging strategies is explained on the example of skidding tractors. The most important topic is to define off-road vehicle properties with their expected impact on the environment. Like all others, the strategy of skidding is the main part of logging, or rather the strategy of development techniques is the top of a pyramid whose base is composed of forestry routine, operations and tactics. The circle of demands for a new product starts with the choice of mode of operation or adequate technology. After defining these items, the selection of equipment takes place as well as their connection to environment. As to the feasibility of skidding strategies, we have learned from our own experience that some adverse requirements have been crucial. In choosing and application of soft skidding tractors, many questions arise related to machines and equipment, such as: machines and devices allowed to be applied in forests; testing laboratories and measuring laboratories accredited for issuing certificates of validity for technical devices used in forestry; the ways of directing the dependencies between adaptability and versatility of the equipment, etc. Out of 1,000 Croatian forestry tractors, one third are special forest tractors (skidders, forwarders), about 270 tractor trailers; two third are adapted agricultural tractors. The analysis of four skidders is given - two adapted farming tractors and two medium-sized skidders. It is based on the comparison of some technical properties: longitudinal and side stability, clearance, dependency of the motor mass and power, winch pull etc. Some of these parallel analyses were made by entering the data of the tested skidders into the previously made database of eighty skidders of different dimensions. The skidders used for thinning operations in stands should have some specific properties, such as small width and height, satisfactory stability, small turning diameter and high environmental friendliness. Furthermore, the computation of the limited load haul has been made based on three criteria, longitudinal stability, rear axle carrying capacity and steerability. Skidding operations on final cutting site represent a different situation. The next step of investigation is the field testing on experimental strip road.There is still a lot to do to reach the solution of all skidding problems, e.g. * to make the choice of the work method with the best choice of techniques; * to improve utilisation in logging operations with the application of varying levels of technical skills, organisation, education and maintenance; * effective system of supervising the quality of environmental care; * interdependent obligations for protection of forestry against tractors endangering its production; * overcoming the problem of need for little series as well as many adverse demands of construction parameters - all these factors, as well as many others, must be considered when choosing the European model for the considerable part of state forests. Finally, reasonable strategies will help the Croatian forests to remain an irreplaceable element of its landscape, economy and culture.

skidder; adapted agricultural tractor; morphological analysis; mountain forest thinning; theoretical tractive characteristic

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