The first attempt to use a construction crane for logging was made after a windthrow when the tangled trees were lying in all directions. Because of the great hazard to fellers in salvage cutting and the necessity to disentangle the trees, it was decided to cross-cut the trees only once next to the root collars so that the overturned rootstock could fall back to its natural ground position (so as to help prevent soil erosion) and thereafter to extract the trees with a construction crane and to process them by means of a wood processor on the forest road. (see Photo 10).
Photo 10. Logging by construction crane after a windthrow where trees were lying tangled and in all directions.
Long-term planning of logging combined with processing operations is necessary to fully utilize the equipment. Apart from internal considerations, external factors should also be taken into account. These would include fully utilizing rented equipment and preplan-ning several crane operations so as to reduce transfers to and from the various operation areas, which otherwise would involve additional logging and operational costs.
Since in Austria the road network was started at a time when the clear felling system was in use and is nearly completed today in most forest enterprises, it must be considered in predetermin-ing the suitable logging system. Due to the comparatively small radius of the construction crane its use seems to be rather limited at first consideration, but there are likely to be more areas suitable than one would think for the above mentioned logging equipment.
Also, in long-term planning for logging operations, maps - such as those used for forest manage-ment regulation and show-ing suitable logging systems for all areas of the forest estate - should be made available. Hence, after the regulation of the areas where felling is to be done, the operation of machines or machine combinations can be arranged according to proposals contained in the map regarding time and terms of operation.
The operational planning for a construction crane operation should include:
· choice between the use of modified full-length method or whole-tree method;
· location of harvesting areas for the next construction crane operation;
· optimal number of workers;
· locating sites, including preparations for setting up;
This operational plan has to be prepared before felling so that clear instructions can be given to the fellers.
The decision concerning the use of the modified full-length method or whole-tree method predetermines all other subjects.
Harvesting areas suited for logging by construction crane and for the harvesting system chosen need to be selected in sufficient numbers in order to utilize hired machines for several days. In this case, as stated above, the costs involved in transfers to and from the operation area can be distributed over a higher volume of logged timber, which would subsequently decrease the total production costs per unit.
According to the harvesting system chosen and the tree diameters at specific harvesting areas, the equipment needed for cross-cutting the long logs or for further processing, has to be selected. If the modified full-length method is applied, cross-cutting at the landing will be done by a feller equipped with a heavier chain-saw suited for large trees.
When the whole-tree method is used, a wood processor should be selected so that the maximum capacity for which it was designed corresponds to the tree diameters at the harvesting areas. A sufficient supply of trees for processing has to be assured so as to fully utilize the hired processor.
The optimal number of workers depends on the harvesting system chosen but the minimum as well as the usually optimal number is two: one assistant at the final cutting area and a second assistant at the landing site. A second assistant at the felling site to help pull out the equipment may be useful in extending the radius of crane action, but this can be recommended only for developing countries with comparatively low labour costs. A second assistant at the landing site is usually not required, even if the modified full-length method is used and if the long logs have to be cross-cut twice or several times, provided that the load size is one piece. Moreover, safety hazards will also be reduced if only one assistant is present at the landing site.
The locations for setting up the crane are predetermined by the radius of action but other criteria - such as the best possible field of vision for the crane driver and adequate road widths - should be taken into account when locations are selected. Due to the high rental fees per hour for the construction crane, the locations for the crane operation have to be well prepared so as to avoid an increase in logging costs.
Since the construction crane and wood processor are set up at the forest road, the outfeed piles will be placed on and next to the road so that hauling can be carried out simultan-eously; this will enable the machines to leave the operation site after completing the job. This is of utmost importance in order to avoid additional costs due to waiting periods for the machines, especially if the settings are located on a dead-end road or in case the vehicles need to go a long roundabout way in order to leave the operation site.
Despite high rental fees which might consequently increase logging costs dramatically if serious delays occur, the use of construction cranes for logging can be recommended for small-scale use under the following preconditions and situations:
· high density of road network due to the comparatively small radius of action;
· preservation of natural regeneration;
· "relatively"small amount of timber volume per harvesting area which favours logging equipment with short installation time;
· inaccessible terrain due to slope gradient, moisture of soil or obstacles;
· salvage cutting at windthrow areas;
· planning and supervision of construction crane and wood processor operation by the forest staff have to be assured.
Finally, it is recommended that all equipment used should be fully utilized not only in terms of adequate supply of trees but also in the employment of skilled operators familiar with particular operating conditions in forest areas. Further time studies should be undertaken to assess logging perfor-mances of construction cranes in various areas in order to optimize construction crane operation according to specific site conditions.
APPENDIX 1. SLIDE SET - to accompany the FAO Forest Harvesting Case Study,
USE OF CONSTRUCTION CRANE FOR WOOD EXTRACTION IN
This slide set is a complement to the report on the case study carried out in a private forest enterprise in the Republic of Austria in Decem-ber 1993 by the Department of Forest Engineering, University of Agriculture - Vienna, Austria.
The purpose of the study was to assess the productivity and costs of a wood harvesting system appropriate to silvicultural systems with natural regeneration.
1. Forests of Austria
Austria is a mountainous country rich in forests: 46% of the land area is covered with forests dominated by coniferous trees; only 36% are broadleafed and mixed forests. The annual increment in timber estimated by the forest inventory is about 19 million m3, but the annual harvesting is only approximately 12 million m3 of timber.
2. Location of the case study
The case study was carried out at two harvesting areas with a 105-year-old and a 75-year-old stands of Spruce and Picea abies, respectively, amply supplied with natural regeneration in the understory. The areas were located between 470 and 480 m in altitude in Carinthia, the southernmost federal state of Austria. The average volume of the trees logged by means of construction crane was 1.24 m3.
3. Forest roads
Forest accessibility is provided by approximately 55 m of road per ha with a formation width of 6 m, carriageway width of 4 m and types of construction corresponding to the usual forest road standard in Austria. Construction cranes like the FAUN RTF 40-3 can certainly be used on these forest roads during dry seasons or when the ground is frozen. Problems concerning the road-bearing capacities might arise during wet seasons.
The trees have to be felled so that they point toward the location where the construc-tion crane is set up. In this case the distance from which the crane operates would be the extraction distance plus the length of the felled trees. The felling operation must be carried out very carefully so that natural regeneration is preserved. Felling has to be finished before the logging phase starts in order to avoid interference in the logging operation.
5. Setting up at the forest road
Once the driver has reached the place where the crane is to be set up, he must manoeuvre the vehicle so that it stands at a right angle to the road's center line; this will provide maximum machine stability during the operation. The front of the vehicle should be pointing opposite the work area since over-front lifting might damage the driver's cab.
6. Setting up at the final cut area
Provided the terrain is accessible and the ground is frozen, the construction crane can be set up on the felling site, about one boom length from the road thereby extending the radius of crane action.
7. Supported operation
Once the vehicle is in the correct position, the outriggers must be extended and set up on firm level ground so as to stabilize the operation, hence providing maximum lifting capacity.
The ground may need to be prepared so as to be level in case the outriggers have to be set up on forest ground. Square-sawn timber between outriggers and ground create a level surface and help to distribute the pressure evenly.
9. Extraction distance
The optimum extraction distances are within the radius of boom length plus the hoisting equipment's length.
The assistant at the felling site is hooking the trees or assortments with log tongs. The tree diameters determine the proper size of the log tongs.
The log tongs can easily be removed by the assistant at the landing. Protective gloves and helmet are absolutely necessary for the assistant in handling the metal log tongs and as a safety measure against the danger of falling limbs from the lifted load.
12. Driver's cab
The construction crane is suitable for the operator because it meets ergonomic principles and requirements. Its design and safety features assure convenient and safe operation which are prerequisites for the operator's sustained performance.
The average time required for the dismantling operation is 15 minutes, which is about half the time needed for setting up the crane.
14. Telescoping boom
After joining the hoisting equipment to the hook block of the stabilized crane the telescoping boom can be extended (maximum boom length 30 m, radius 28 m).
Different steering possibilities provide high manoeuvrability and small turning radius of the 3 axle all-terrain crane FAUN RTF 40-3.
16. Final cut area
The assistant who will be hooking the load has to arrange the trees or assortments for logging; in order to avoid lateral pulling he also has to direct the operator by radio so that the boom is aligned to the felled trees which have to get logged.
17. Load size
It is not advisable to transport more than one tree or assortment simultaneously. One reason is the impos-sibility to align the boom to more than one tree at the same time and avoid lateral pulling. Another reason is the difficulty during touch down of a load consisting of logs with different lengths.
18. Landing area
The crane driver is able to place the tree or assortment exactly in the desired direction.
19. Lifting the load
Lifting the load is the critical phase of the logging operation. A swinging boom caused by lifting a tangled tree makes the driver apprehensive of overturning the vehicle and increases his mental strain as well.
20. Load transported: vertical
To transport the trees or long logs in a vertical position means with "raised head".
21. Load transported: horizontal
The log tongs are fixed at both ends. This could be useful in preserving natural regenera-tion from damage but it requires that the trees lie in the optimal radius; otherwise the trees have to be transported in a vertical position first and rehooked afterwards.
22. Hoisting equipment
The hoisting equipment used consists of two 6 m long ropes with log tongs of different sizes on the one end and are connected with a loop on the other end to a 6 m long synthetic sling which is joined to the hook block. The hook block hangs from a rope about 5 m from the top of the boom; this increases the effective radius of action to 45 m, depending on the slope of the terrain.
23. Length of assortments
In relation to the height of the natural regeneration, maximum transportable length should not always be completely made use of so as to assure the best possible preservation of the young trees.
24. Load volume
A significant advantage of the FAUN RTF 40-3 and other comparable types of construction cranes is that they have a fully automatic overload protection device so that the safety hazards are reduced to a minimum.
25. Infeed pile
When the whole-tree method is used a wood processor should be selected according to its maximum design capacity and the tree diameters at the harvesting areas. A sufficient supply of trees for processing has to be assured so as to fully utilize the wood processor.
26. Wood processor
The one-grip crane processor STEYR KP 40 is a machine designed for continuous operation with trees up to 40 cm butt-diameter and can be used in combinaiton with other machines.
27. Carrier vehicles
The one-grip crane processor can be mounted on different carrier vehicles such as trucks, skidders or excavators. Here it is mounted on a wheeled excavator.
28. Site after operation
When setting up the wood processor on a forest road, the operator has to carefully pile the produced assortments and debris so as to keep a clear work space for the machine.