PRELIMINARY TECHNICAL TIME STANDARDS FOR HARVESTERS WORKING IN PREMATURE AND MATURE STANDS

Jiří Dvořák¹, Pavel Karnet^2
1 Department of Forest Harvesting, Czech University of Agriculture in Prague, Czech Republic
² Czech University of Life Science Prague, University Forestry Establishment at Kostelec n.C.l., Czech Republic

ABSTRACT

Assessment of performance standards for logging operations is a foremost task of the technical standardization. In this paper we deal with preliminary technical time standards for harvesters working in particular felling&technology and natural conditions. Monitoring of unsuitable time utilization is hand in hand with elaborated correction proposals another objective of this work. The chronometry was analyzed during the work of medium-scale harvester Timberjack 1070 in natural environment of Krusné hory during felling works in premature and mature forest stands. Preliminary paper is worked up for tree-volume of coniferous species from 0.44 to 0.73 m³, which require for manufacturing operation time from 91 to 118 seconds. More operation time is needed when greater trunks are processed. Total standards lies for intermediate (improvement, advanced) fellings within the interval 0.033-0.043 Standard hour/m³ for main felling 0.030-0.039 Sh/m³ depending on tree-volume. Propounded findings should not be generalized; they are typical for the use of medium-scale harvesters in such natural conditions that are similar to nature territory Krusné hory.

Key words: logging operations, chronometry, Timberjack harvester, time standards .

INTRODUCTION

There were working 137 harvesters and 282 forwarders in Czech forests in the begining of 2005 (from those 75 low-scale forwarders Vimek and Terri) [7]. Harvesters and forwarders of medium-scale level (75-140 kW) are very popular for its possibility to be used in stand felling from the 4^th age grade since the stand sectioning is uniform for all cuttings. Development of number of harvesters used in the Czech forestry reflects the development in western European countries. Succesful use of harvesters in terms of achievment of maximal timber yield depends on practical operator’s experiences and skills gained in the long-term period. Till now there have not been prepared and suggested performance standards especially for short-term providers/owners of felling&skidding machines in the Czech Republic whence it follows that harvesters are used in inappropriate service conditions. Therefore as a result is presented unqualified performance assessment, which in total affects the work productivity and number of machine repair works.

OBJECTIVES AND METHODOLOGY

The neglect of work organization leads to a disparagement of a time demanded by felling&skidding machines. Continuous work ensures maximal volume of the timber production. The investment return growths hand in hand with increasing timber production. There have already been worked out norms for the purposes of different ways of felling but not yet for harvesters. The application of these norms serves the purposes of work planning, preparation of rolling stock and manpower planning. Market research demonstrates heavy time utilization of felling&skidding machines (Tab.1), but it does’t however give optimal utilization of annual time fund and its distribution between general and major time. Harvesters are used for 273 working days in the Czech Republic from which transfers among workplaces take 5%, and non-standard servicing take 17%. This presents an average 2.2 hours of 9.8 hours, which is the average daily working time of an operator. If we consider the minimal safety break, which is given by law, and the blackout time, the general time (not representing major efficient time) is 27.5% of 1 shift. Average number of forwarder working days is 255 a year. Analogical annual utilization of forwarder Timberjack 1010 is also mentioned in Poland (up to 267 days a year) [6]. The task is to optimize major time utilization to obtain maximal machine performance and to eliminate unnecessary operations.

The research is focused on elaboration of time snapshot of harvesters working in intermediate and main fellings in similar natural conditions of Krusné hory. Premeasuring includes performance observation, working procedure and working efficiency per a time unit. The felling is convenient also for the “task giving” because it presents unchangeable regular working procedure within the marked trees are felled and manufactured.

Observation of working assignment is divided into 2 sections, which are in consonance with time studies carried out in forestry [3] and [5]:

1. Time snapshot of the operator’s working day includes:

1. Setting of working orders, work preparation and work termination within the shift,

2. Logging,

3. Hygienic and biological breaks,

4. Machine service and repair,

Snapshot of the working day was carded on special observation sheet for no determinable sequence of working operations or work interruptions during a shift in contrast to chronometry.

2. Chronometry – time snapshot of the harvester operator’s work stages includs:

1. Moving from and to a new felling position,

2. Approaching of the felling head to the trunk and the clutching of the tree,

3. Felling and timber processing,

4. Lengths and width measuring is covered in add c)

The separation of the operative and general time is shown in Fig. 1.

Transition from one working operation to another is determined by cut-off points [5]. The moving from and to a new felling position starts with harvester take-off and terminates with its cut-off. Approaching of the felling head to the trunk is conditioned by the harvester cut-off although some skilful operators are able to approach felling head even during the moving of a harvester. Time registration together with the movement of hydro-manipulator would lead to time overlapping with the machine movement from and to a new felling position. Approaching of felling head and tree clutching were terminated by fixation at the stem base. The cut-off point for cutting and processing of trees is the start of variation movement of the saw to the trunk and terminated by the harvester take-off to another marked tree.

Time snapshots were measured during the work of medium-scale harvester Timberjack 1070 whose share is the highest in logging operations performed by harvesters (Tab. 3). Particular standard is referred to coniferous species and is based on tree-volume of processed trunks.

Average tree-volume of processed spruces, represented by 45% in measured felling operations, was 0.47 m³ in intermediate felling. The tree volume in mature stands was 0.78 m³ and spruce was represented by 63%. The number of coniferous species manufactured by harvesters was 80% in intermediate fellings and 92% in main fellings. Harvesters did integrated assortments manufacturing, which included in this case the production of 2-meter long pulp wood, 3 meter long aggregates and 4-5 meter long roundlogs.

RESULTS

There were 120 trees in premature and mature stands measured, which represented 61.50 m³ of manufactured timber. The total time had to be divided into general and major time. The general time comprises of hygienical and biological breaks including lunch and snack breaks. Furthermore the preparation of work, work orders, machine service and repair are involved in this general time. Although this time might be viewed as “wasted time” we see it as useful and inevitable. The general time for work preparation is excluded from time snapshot of work operations and is included only in the day snapshot of operators. The general time also includes obstacle removal from skidding lanes before the beginning of felling activities; such an operation is for harvester technology exceptional. This time can be assumed as evitable if the working place preparation had been done properly i.e. layout of clam lines. This time is separeted from the major time, which includes proper working time.

The preparation time of a harvester work includes a) moving from and to a new position, b) approaching of the felling head and the clutching of the tree. These operating activities comprise of tree fall direction determination and debranching of the tree base if branches hinder the cutting. The most important is the major time comprising felling and timber processing. This work is performed continuously (felling, debranching and stacking) or concurrently (debranching, measuring and sorting). Therefore these operations cannot be observed individually and are totalized into major time.

There were measured and processed 90 trees in premature stands and 30 trees in mature stands for the investigation of the time of particular operations. Average work operation time is summarized with its share of the total operating time sum in the table 4. It is perceptible how the stand age influences the necessary time for the placement of the harvester in new position. In mature stands it takes 40.5 seconds in contrast to premature stands where this operation takes only 18.8 seconds. The longer moving time in mature stands is affected by wider spacing among trees and by felling of more trees on 1 standpoint.

In premature stands the time for approaching of the felling head and the clutching of the tree is enlarged about 0.8 second compared to time reached in mature stands. In thinnings the longer time is influenced by higher stand density and lower ability of the hydraulic crane to manoeuvre because of likelier damage to trees. Younger forest stands are often branched.as far as the ground. Operator performs debranching of the branched stem base, which also slows down the operation time.

Last but not least is the felling and timber processing time, which takes 70.0 seconds (77.3 % of major time) in premature stands and 76.6 seconds (64.9% of operating time) in mature stands. The difference, which makes 7 seconds, was not statistically significant. Different time is caused by bigger tree-volume (up to 0.29 m³) and thicker branches in mature stands. It is often inevitable to repeat debranching of the stem base due to abortive first cut of thicker branches. We may not forget to consider more demanding manoeuvrability with mass trees. These trees are frequently underpicked and moved over the ground, what might particularly take part in time enlargement.

Respective production process is connected not only with operative time (major and secondary) even with next general times whether eliminable or non-eliminable. This time is summarized in the daily snapshot (Tab. 5). Daily time snapshots were performed separately for premature and mature stands. Nevertheless statistical significance between measured general times was not proved, thus higher production demandingness in premature or mature stands, leading to necessity of longer breaks, cannot be approved. Time snapshots were measured in five days in both premature and mature stands. Average work of the harvester in premature stands is 7.7 hours a shift. In mature stands the harvester worked 8.2 hours a shift that made the difference 30 minutes. From the individual parts of snapshot the biggest difference makes the working operation itself which presents 1.5 hours “in favour of” main felling. It can be assumed that operator’s mental load is more demanded working in premature stands because of more accurate work requirements; finally leading to lower efficiency in contrast to main felling in mature stands. Hygienical and biological breaks were found to be the same in both stand types with little time difference (5 minute), the time for lunch break given by law was met. The rest of time serving e.g. the work preparation, job orders, machine repair and servicing looks to be accidental regardless of planned thinning or main felling.

Statistical analyze approved statistical significance only between times representing the approaching of the felling head and the clutching of the tree in intermediate and main fellings (Tab. 6). This time unit represents an inconsiderable fragment of major time (0.8% in intermediate and 2% in main felling) therefore statistical significance was not considered. There were summarized measured times for further analyzes with respect to the tree-volume. Operative time is proposed according to the tree-volume which is from 0.44 m³ to 0.73 m³ (Tab. 7 and Fig. 2).

Production time needs to be extended by general time, which includes e.g. work preparation time, breaks, machine service and repair. With respect to wide variability of this general time in intermediate and main fellings the proposed time standard is divided and defined for each felling individually. The intermediate felling time consist of 7.7% for preparation works, 5.5% for hygienical and biological breaks and 18.4% for machine maintenance. The time-share for preparation work is lower in main felling – 1.7% because it is not necessary to do the checking of clam lanes precisely, distinguish target tree specie and to perform more detailed survey of the stand accessibility. In mature stands the work preparation is connected only with operator’s gaining of knowledge of felling area boundaries and thus preparation time-share is lower about 5% in comparison with tending felling in premature stands. The time of hygienical and biological breaks doesn’t change in accordance with type of felling.

Surprisingly the time for machine service and repair was higher in improvement fellings than in main fellings where it would be expected higher time consumption for repairs because of bigger overload (Tab. 5). The hydraulic system is more overloaded by branches of trees standing along clam lanes and by branches of trees that are approached by the felling head in fully branched premature stands. Moreover this results into fouling of engine and machine parts, which prolongs the time of maintenance. The time demanded for maintenance of machines after performance of intermediate felling makes all together 18.4% out of production time and it is 36 minutes longer in comparison with main felling which take 48 minutes and represents only 9.8%. Major time (from the Table 7) was extended by general times and all together represents proposed “standard hour time” necessary for the processing of conifers by harvester technology considering tree-volume of processed tree and intermediate and main felling (Tab. 8).

Measured efficiency of the harvester Timberjack 1070 ranges from 13.3 to 16.0 m³/hour in premature stands and from 14.7 to 18.7 m³/h in mature stands within tree-volume 0.44 – 0.73 m³. [2] shows the efficiency in Czech forestry from 19 to 32 m³/h depending up mean tree-volume 0.50 – 0.75 m³ with respect to clam line width, felling intensity and slope gradient. These factors must be adjusted in operative performance standards by percentage arrangement. Different performance between harvester Timberjack 1070 (126 kW) and Timberjack 1270D (160 kW) affects without any doubt the harvester efficiency. Smaller harvester Rottne 2004 shows the efficiency 13.5 m³/h provided that mean tree-volume is 0.50 m³ and felling intensity reaches 30 m³. Production performance increases to 15.5 m³/h when felling intensity is doubled.

The measured efficiency can be compared with the performance of tracked harvester Valmet 911 Snake (130 kW) [4]. Average machine performance is 18.4 m³/ha. Technical construction of bogie plays probably an important role in comparison among machines.

CONCLUSIONS

Time values in the standard-hours table graduate depending on tree-volume of felled conifers. For the use of standards based on distinct tree-volume levels it is necessary to ascertain mean tree-volume of felled trees. Standards had to be differentiated for intermediate and main fellings with respect to statistical significance of differences between general times.

Preliminary performance standards are elaborated for a lowland terrain with the maximal slope of 20%, accessible with no obstacles exceeding 50 cm or the spacing among obstacles is wider than 5 metres and bearable ground. Snow cover should not exceed 20 cm. Technical&technological conditions are also set by average spacing among trees which is not wider than 10 meters. As the normal felling cannot be considered such a felling in which trees not growing in the canopy closure and border trees are cut. Performance standards are allowed to be used in incidental felling as well if set forth above conditions is met and cutting resembles planned felling. Standards don’t include the time devaluating operator’s efficiency in such cases where the protection of young-growth stand or self-seeding is required.

The results have shown that harvesters are preferred to be used in planned main felling presenting lower production time demandingness about 9.1–9.3 % in comparison with intermediate felling. The total time of felling working cycle is concurrent for both the mature and the premature stands, the difference makes 27.4 seconds.

Medium-scale harvester has come out to be universal for felling in mature as well as in premature stands, the harvester is only limited by the width of tree base up to 55 cm. Exceeding this limit leads to statistically unimportant time delays especially in tree cutting and processing of stem base assortments. The increasing tree base width implements damages of most valuable part of the tree by departing or pulling of fibres, which results in devaluating of butt log. This is why it is recommended to use these harvesters only for first main fellings.

REFERENCES

1. Dvořák, J., 2005. Harvestorové technologie a poskození stromů při jejich pouzití, Lesnická práce 7/2005, [Harvester technologies and tree damages caused by harvester work] Kostelec nad Černými lesy, s. 30-32, [in Czech].

2. Neruda, J.-Ulrich, R.-Valenta, J., 2006. Analýza faktorů výkonnosti středních harvestorů, [Analysis of efficiency factors of medium-scale harvesters], In: Trendy lesníckej, drevárskej a environmentálnej techniky a jej aplikace vo výrobnom procese, TU Zvolen, 8 s., [in Czech].

3. Schlaghamerský, A., 1994. Zeitstudien, [Time Study], Fachhochschule Hildesheim/Holzminden, Fachbereich Forstwirtchaft in Göttingen, 122 s., [in Germany].

4. Steinmüller, T. – Stampfer, K., 2002. Ein Produktivitätsmodel für den Harvester Valmet 911 Snake, [Performance model for harvester Valmet 911 Snake], 33. Internationales Symposium Teffen der Sektion Forstechnik des Verbandes Deutscher Forstlicher Versuchsantallten, Sopron, 9 s.

5. Vichr, V., 1956. Cesty k technickému normování práce [Ways of technical job standardization], Vydavatelstvo ROH, Praha, 160 s., [in Czech].

6. Zychowicz, W., 2005: Efficiency of exploitation of the vehicle that can by used alternatively as a forwarder or clam bunk skidder, Zeszyty Naukowe Akademii Rolniczej im. H. Kollataja w Krakowie nr. 419, Krakov, s. 291-298.

7. Ministerstvo zemědělství ČR, 2005. Zpráva o stavu lesa a lesního hospodářství České republiky v roce 2005, [Ministry of Agriculture: Report on the State of Forests and Forestry in the Czech Republic by 2005], MZe v Praze, Praha, 155 s. [in Czech].

Accepted for print: 15.12.2006

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.