Productivity Models for Operational Planning of Timber ...assortments«, which was financed by the state company »Hrvatske {ume« d.o.o. (»Croatian Forests«), the process of development

Productivity Models for OperationalPlanning of Timber Forwarding in Croatia

Igor Stanki}, Tomislav Por{insky, @eljko Toma{i}, Ivica Tonkovi}, Marko Frnti}

Abstract – Nacrtak

In the area of Croatian lowland forests, forwarders are usually used for extraction of timberassortments. Within the project »Systematization of norms for the production of timberassortments«, which was financed by the state company »Hrvatske {ume« d.o.o. (»CroatianForests«), the process of development and implementation of new productivity norms forforwarders was carried out.

Initially, for the execution of the research, it was necessary to gather data about technicalcharacteristics of forwarders most frequently used in Croatia, but also around the world. Themorphological analysis was performed and it was the basis for the classification of forwardersinto classes. Three classes of forwarders were obtained after cluster analysis and load capacityappeared to be the most important factor. Machine performance was evaluated on 30 researchsites. The standard method of time study (snap-back chronometric technique) was used.During the recording process, data of factors influencing forwarding (stand and terrain con-ditions) were collected.

After analyzing the collected data, it was determined that the forwarding productivity de-pends on the forwarder class, average extraction distance, load characteristics, terrain andstand conditions. Regression analysis was used for identifying the time consumption of in-dividual work components, and the productivity model for forwarding was developed.

The obtained model was implemented into the application HsPPI. This is a part of the infor-mation system developed by IT Department of the state enterprise »Hrvatske {ume« d.o.o.and is used for production planning in timber harvesting. The system is based on dBase IVdatabases and two main program modules. The main parts of the system are: tree markingdata, assortment structure plan, production plan (felling, processing and extraction) andsales plan. Within a part of the production plan there is a module for calculating producti-vity norms for timber forwarding.

Keywords: forwarder; productivity norms; planning; lowland forests, Croatia

1. Introduction – Uvod

In the Republic of Croatia, state forests and forest-land cover an area of 2,106,917 ha and most of them(96%) are managed by the state enterprise »Hrvatske{ume« d.o.o. (»Croatian Forests«; H[; Anon 2006).From the economic aspect, selection and even-agedforests are the most significant forests of high silvi-cultural form. In the Republic of Croatia timber ex-traction is mainly mechanized, while felling and pro-cessing is motor-manual and carried out by chainsaws(Bojanin and Krpan 1997). In Croatian mountainousselection forests, skidders are used for timber extrac-tion (Sabo and Por{insky 2005). On the other hand,in cases of even-aged forests in hilly and lowland

areas, depending on the stand and terrain conditions,skidders and forwarders are used for timber extrac-tion, while the use of adapted farming tractors andtractor assemblies has decreased (Krpan 1996; Beuket al. 2007). The lowland area of forests and forest-land owned by the state amounts to something morethan 322 thousand ha (Pentek et al. 2011). The low-land forests are of particular importance for this re-search, as forwarders are mainly used in this part ofCroatia. Lowland forests consist of forest stands of thepedunculate oak (Quercus robur L.), narrow-leaved ash(Fraxinus angustifolia Vahl.), black alder (Alnus gluti-nosa [L.] Gaertn.), willows (Salix sp.), poplars (Populusalba L., Populus x euramericana clones) and commonhornbeam (Carpinus betulus L.). Annual removal

Croat. j. for. eng. 33(2012)1 61

Original scientific paper – Izvorni znanstveni rad

amounts to more than 1 mill m³ of wood (Anon2011). The figures might not be impressive; however,wood from these forests (pedunculate oak) has beenachieving high prices on the roundwood market,which is where the importance of the lowland forestscan be seen at its best. The aim of this research is toestablish the system of planning timber extractionfrom late thinning and shelterwood felling of low-land forests in Croatia.

2. Problematics – Problematika

Forwarders are self-propelled vehicles intendedfor the transport of trees and their parts loaded in thevehicle bunk area (ISO 2009). The development ofthe first forwarder started in Sweden around 1950s,and their use in Croatia started in 1971 (Slabak 1983).Forwarders were originally used in cut-to-length tim-ber harvesting, where the felling of trees was per-formed by harvester, and extracting by forwarder. InCroatian forestry forwarders are mostly used in low-land forests, particularly for the extraction of timberfrom shelterwood felling and late thinning (Por{in-sky 2002). Therefore, for investigating forwarders’performance in Croatia, the lowland forests are themost significant as they cover almost 25% of the totalarea covered with high forests (Krpan 1996). Secon-dary (technical) productivity in forestry is significantfor the research of forest operations (Löffler 1989).From a scientific point of view, the research of forestoperations includes the study of timber harvesting,ergonomics, mechanization, construction, economicaspect and planning of operations, all within theframework of a sustainable forestry development(Samset 1992). The research of forestry operations,and hence also timber forwarding, is based on timestudy and on monitoring the influencing (quality andquantity) factors, data analysis, and mathematicalmodeling of time consumption of individual com-ponents of the working process (Samset 1990). Simi-larly as other forms of timber extraction, forwardingalso has the characteristics of a cyclic working process.

Forwarder efficiency is affected by numerous fac-tors. The most important factors influencing the ef-ficiency of timber forwarding is the travel distance(Sever 1988). With the increase of the travel distance,the impact of the load volume on the vehicle pro-ductivity is also increased (Raymond 1989). Apartfrom the forwarding distance, productivity is alsoaffected by the average assortment volume (numberof pieces in the load) and quantity of timber on a fel-ling site, which is more pronounced in thinning stands(Tufts and Brinker 1993; Tufts 1997). The highestshare of time consumption in forwarder operationsis related to the so-called terminal times, and namelyloading and unloading of timber (Minette et al. 2004).

Optimization of load volume and forwarding dis-tance, and giving preference to downhill forwardingare the key factors for improving the productivity offorwarders (Tiernan et al. 2004). Terrain slope higherthan 30% considerably decreases the productivity offorwarders because on such terrains vehicle mobi-lity is limited (Zimbalatti and Proto 2010). Terrainclassification aimed at determining the optimummachine for timber extraction shows that in hilly--mountainous area, too, the share of timber forward-ing is quite considerable (Miheli~ and Kr~ 2008; Pen-tek et al. 2008). On steep terrain, up to 60%, it ispossible to use forwarders with winch, the so-calledcable forwarders (Kühmaier and Stampfer 2010). Theuse of semi-tracks in conditions of limited soil bear-ing strength increases fuel consumption but provi-des vehicle mobility (Wästerlund et al. 2011). Apartfrom travel distance, load volume and terrain condi-tions, forwarder productivity is also affected by thetype of felling, length and type of assortment, dri-ver’s skill and knowledge, as well as characteristicsof hydraulic crane and vehicle load space (White2004). The increase of the average assortment volu-me and terrain slope in travel direction (downhillforwarding) result in the decrease of time consump-tion (Ghaffarian et al. 2006). The density of secon-dary forest roads (forest trails) also affects the for-warding productivity (Mederski 2006). Up to dateplanning methods, i.e. spatial optimization of workingcycle shifts based on data on quantity and locationsof assortments and possible travel areas of the fellingsite also increase the timber forwarding productivity(Flisberg et al. 2007). Comparative research of skid-ding/forwarding machines carried out in stands ofsmall coniferous trees showed that, in terms of costs,figures speak in favour of timber forwarding, asforwarder productivity is twice higher than the pro-ductivity of the skidder with winch (Li et al. 2006).Forwarder efficiency depends on the type of thevehicle used, i.e. on its nominal carrying capacity, asforwarders of higher carrying capacity achieve low-er costs and higher productivity per product unit(Jirou{ek et al. 2007). Nowadays forwarders are notconceptually different from those of half a centuryago, but they have made serious progress in terms ofenvironmental soundness, ergonomics and steeringautomation (Pandur et al. 2009). One of the ways toincrease productivity is the use of dynamic systemfor changing the volume of the bunk area (Brunberg1999), i.e. its height and width (Brunberg 2001). At-taching the trailer with the loading space behind therear end of the standard forwarder may increase thesystem productivity (Lindroos and Wasterlund 2011).Investigations were performed of the use of »flats«or »swop bodies«, where timber is not unloaded

62 Croat. j. for. eng. 33(2012)1

I. Stanki} et al. Productivity Models for Operational Planning of Timber Forwarding in Croatia (61–78)

from the forwarder nor loaded into the truck, as theyare used with both kinds of transport, thus increas-ing productivity and simplifying primary transportof timber, but with increased costs (Freitag and War-kotsch 2011). Considering the productivity and costsof timber harvesting machines at an annual level, theshare of the travel of machines between felling unitsis quite considerable, so when planning, the possi-bility of leasing trucks for the transport of machinesshould be taken into account (Väätäinen et al. 2006).

Productivity of timber forwarding is higher thanthe productivity of timber skidding in lowland fo-rests of Croatia, and the increase depends on standand terrain conditions and ranges between 28 and126% (Bojanin and Krpan 1994). The operation offorwarders in Croatia, unlike the Scandinavian as-sortment method (CTL), makes no use of felling andprocessing machines. This is the effect of naturalfactors (natural forests, trees of large size, consider-able share of broadleaved trees, etc.), but also oftradition (Bojanin and Krpan 1997). The above saidis the cause of a different approach to gathering andprocessing data, selecting the influencing factors andmodelling the working process. One of the problemsarising is the definition and determination of themean distance of timber forwarding. Some authorsconsider that the distance of timber forwarding isthe distance between the roadside landing and thepoint in the felling site when the bunk area is halfloaded with timber (Kuitto et al. 1994; Nurminen etal. 2006). Accordingly, the mean distance of timberforwarding would be equal to the sum of traveldistance of unloaded vehicle and half the travel intimber loading i.e. the travel between the loadingpoints (Suvinen 2006; Väkevä et al. 2001). Wheninvestigating forwarders in Croatian lowland forests,the distance of timber forwarding was considered tobe the arithmetic mean of the sum of distances tra-

velled by fully loaded and unloaded forwarder, whilethe time consumption of the vehicle movement dur-ing loading process was defined depending on fel-ling density, i.e. net timber volume per hectare (Por-{insky 2002, 2005; Stanki} 2010).

The production of timber assortments has beensupported by information systems used by the statecompany H[ for monitoring and recording the pro-duction of timber assortments. The information sys-tem has been continuously developing for twentyyears, since the founding of the company, and it is theresult of the development program of the company’sIT Department. At the beginning of the develop-ment, the system was based on personal computerswith programs made in computer language FoxPro2.6 for DOS (dBase IV as database). Although thecomputerization of the company has gone a longway from those times, a part of these programs andFoxPro2.6 as program language are still being used,while new programs are being developed for Win-dows operating systems in Visual FoxPro 9.0 andon.NET platform with MS SQL database.

A part of the information system of the companyH[ is the production subsystem, by which all timberharvesting processes are monitored – from produc-tion planning to issuing bills to buyers. HsPPI andHsPro are important parts of this subsystem. HsPPIrefers to the production planning, while HsPro refersto the monitoring of timber assortments production.

The basis of the information flow is in the forestdatabase HsFond that basically represents digitaliz-ed Management Plan Prescriptions. One of the fac-tors is the Harvesting Plan, which represents thebeginning of the production planning. On that basis,the harvesting (sub)compartment is selected, treemarking data is prepared, distribution of markedtrees is entered, harvest is planned out, cut block isestablished, the technology of timber processing ischosen along with the production plans, where thefelling and processing norms, as well as the primarytransport, have to be determined. At the end of theplanning process, the sales plan is developed. Allthese processes are carried out within the HsPPIapplication that H[ uses for the preparation of pro-duction within harvesting.

3. Materials and methods – Materijal imetode

3.1 Classification of forwarders – Razredbaforvardera

A good knowledge of forwarders as means ofwork in the forestry production is of crucial signifi-cance. Many research methods are already known,

Croat. j. for. eng. 33(2012)1 63

Productivity Models for Operational Planning of Timber Forwarding in Croatia (61–78) I. Stanki} et al.

Fig. 1 Forwarding in Croatian lowland forestsSlika 1. Izvoènje drva u hrvatskim nizinskim {umama

from those that determine borderline usability, tothose that study the historical development of itsconstruction. One of the studying methods for themachines used in forestry is the morphological ana-lysis based on the selected geometrical, mass andother factors, on which basis dependencies are cal-culated and opinion on validity of machine selectionis made (Por{insky 1997). One of the first morpholo-gical analyses of off-road vehicles was carried out byBekker in 1956 (Sever 1980). Gradually, the methodwas accepted and is used even today for the evalua-tion of forestry machines or tools, especially by re-searchers from Department of forest engineering ofthe Forestry Faculty Zagreb for investigation of chip-pers ([u{njar 1998), farming tractors (Horvat and[u{njar 2001), skidders (Horvat et al. 2007), hydrau-lic cranes ([u{njar et al. 2007), chainsaws (Por{inskyet al. 2008), farmer winches ([u{njar and Bori} 2008).

In the Croatian forestry, the following forwardersare used most frequently: Timberjack 1210, Timber-jack 1410, Timberjack 1710, Valmet 840 and Valmet860 (Table 1). Modeling of productivity individuallyfor each forwarder would be cost-ineffective, so itwas necessary to group them in classes and analyzethem on that basis. Many forwarder classificationsare already known, and according to them forward-ers are classified by net mass, load capacity or grossmass (vehicle + load, (Por{insky 1997)). The latestforwarder classification found in literature is madebased on their loading capacity (payload) to light(<10 t), medium (10 t – 14 t) and heavy forwarderswith the load capacity over 14 t (Brunberg 2004). Inthis case, the morphological analysis of forwarderfamilies according to their numerical values (dimen-sions, mass, load capacity, etc.) will be used as a basisfor grouping vehicles in classes. The data have takenfrom the obtained and adapted database, only forthe vehicles of the new generation (Lugmayr et al.2009).

3.2 Assortments characteristics – Zna~ajkesortimenata

The Croatian lowland forests are characterizedby a great variety of stand conditions. There is awide range of tree species, from willows and po-plars, over black alder and narrow-leaved ash, topedunculate oak and common hornbeam. The areais characteristic by the assortment method of proces-sing, with forwarding as a special way of timberextraction. The assortment volume is important forobtaining the correct figures of the mean load volu-me that impact the forwarder productivity. The aimwas to obtain the mean assortment dimension, so itwas formed on the basis of trees taken from the treemarking data, that is by connecting the data fromtwo applications of the information production sub-system HsPPI and HsPro. Data on trees marked to befelled and data on processed timber assortments inthe work yards were collected for the yards wherethe extraction has been carried out with forwardersover the last couple of years (Fig. 2). Data on treespecies whose share in the lowlands is low (fruittrees, common maple, lowland elm, walnut, etc.)were left out from the analysis, as well as cuttingblocks with small number of samples. Only the datafor the most important species, based on their sharein the prescribed removal of the Croatian lowlandforests, were taken into analysis: pedunculate oak,common hornbeam, narrow-leaved ash and blackalder. The goal of the analysis is to determine themean assortment volume, mean diameter and lengthfrom the volume of marked tree by the tree species.The stated is necessary to determine the productivityof forwarders in this system of harvesting.

3.3 Forwarder productivity – Proizvodnostforvardera

The research of forwarder productivity was car-ried out in the area of Croatian lowland forests (Fig.2). In this research, the term Object of Study (OS) is

64 Croat. j. for. eng. 33(2012)1


Table 1 Some technical features of investigated forwardersTablica 1. Neke tehni~ke zna~ajke istraìvanih forvardera

Forwarder type

Tip forvardera

Number of wheels

Broj kota~a

Engine power

Snaga motora

Length

Duljina

Width

[irina

Height

Visina

Mass

Masa

Payload

Nosivost

Crane reach

Dohvat dizalice

n kW mm mm mm kg kg m

Timberjack 1210 6 114 9,060 2,640 3,710 11,720 12,000 10.3

Timberjack 1410B 8 129 9,205 2,705 3,700 16,500 14,000 8.5

Timberjack 1710B 6 156.5 10,450 3,010 3,900 17,400 17,000 7.2

Valmet 840 6 124 9,007 2,650 3,780 13,800 12,000 9.2

Valmet 860 6 140 9,170 2,740 3,789 14,300 14,000 9.2

used, which refers to individual stand, that is thecompartment/subcompartment where harvesting iscarried out. Raw data for productivity analysis weretaken from the previous investigations of a total of 30objects; 5 OS (Por{insky 2000) + 3 OS (Por{insky 2005)+ 22 OS (Stanki} 2010). Average removal per OS was199.79 m3/ha, average tree size was 3.22 m3/tree andaverage area of OS was 27.70 ha.

The research of the machine work is based on thetime and work study. The basis is the work and timestudy, division of work process or work phase intoconsisting parts of the shortest possible time dura-tion that can still be measured precisely enough.Contemporary approach to time study presupposesthe implementation of analytical measuring methods,whereby work process is divided under particularschemes into work components with the goal ofsynthesis during data and results processing.

Extraction of timber by forwarders has the cha-racteristics of cyclic work. Each cycle (turn) consistsof four main cyclic work components (unloaded tra-veling, timber loading, loaded traveling and unload-ing of timber), plus work pauses or time consump-tions whose character is not cyclic, but periodic.

Forwarder productivity is modeled by the fol-lowing module:

t = fa sv v

sv v

t tof on l u× +

æ

èçç

ö

ø÷÷ + × +

æ

èçç

ö

ø÷÷ + +

ì 60 60 60 60

1 2 3 4

íï

îï

üýï

þï

é

ëêù

ûúminturn

P =60 3× é

ëê

ù

ûú

V

t

m

hl

where:t – total time, min/turnsof – forwarding distance (offroad), kmv1 – unloaded vehicle speed (offroad), km/hv2 – loaded vehicle speed (offroad), km/hson– forwarding distance (forest road), kmv3 – unloaded vehicle speed (forest road), km/hv4 – loaded vehicle speed (forest road), km/htl – loading time, min/turn (tl=tl1+tl2)tu – unloading time, min/turn (tu=tu1+tu2)fa – additional time factorVl – load volume, m3/turnP – productivity, m3/h

The study of forwarder work time was carriedout by snapback method, using manual digital chro-nometer. Besides the time study, data were collectedof all factors influencing the work process. Forward-ing distance was measured by hand GPS devices. Inorder to establish the forwarder performance, loaded

Croat. j. for. eng. 33(2012)1 65


Fig. 2 Research sites of forwarder productivity and timber assortments characteristicsSlika 2. Mjesta istraìvanja proizvodnosti forvardera i zna~ajki sortimenata

assortments were counted and the number of theidentification plastic tag was recorded in case oflarge sawtimber and veneer assortments. In othercases (with small assortments – pulpwood and longfirewood), direct measurement of processed assort-ments took place, whereby data on tree species, meandiameter and length were entered into a correspond-ing form. The ground bearing capacity was deter-mined for each individual cycle, by visual estimateof the recorder. The soil bearing capacity was studi-ed in line with the modified classification of groundbearing capacity that was already used in similarform within the research of machine performance inareas of the Croatian lowland forests (Por{insky 2000).Under this classification, forest soils were classifiedinto the following load-bearing groups, and it wasapplied in further analyses:

Þ Soil of good load-bearing capacity – firm andmoderately firm soil. It includes dry, frozen oroccasionally wet soil which presents no problemsfor moving vehicles. By a single pass of the vehi-cle, the tracks depth amounts to less than 5 cm,

and by multiple passes the depth amounts up to25 cm, maximum 30 cm. When walking on suchsoil, shoe soles are dry or humid.

Þ Soil of limited load-bearing capacity – soft andvery soft soil. It is a soil that is partly to fullysaturated with water. Walking on it is difficult,tracks of shoes are fully visible. Sinking of vehi-cles into the ground and slipping of wheels areappeared, vehicle speed is reduced, and after asingle pass, the mineral layer of the soil can beexposed. Implementation of semi-tracks on therear wheels of bogie axle and chains on the frontwheels of single axle is recommended to obliga-tory (in extremely unfavorable conditions).

Before starting the recording, an online form forthe input of recorded data was developed. The formwas developed using.NET technology and it couldbe found at the address http://norme.hrsume.hr. Atthe end of the work process recording, each recorderwould register to the stated webpage and enter thedata into the integral database. MSSQL databasewas used.

66 Croat. j. for. eng. 33(2012)1


Table 2 Correlation table of studied values (those bold are significant at p < 0.05)Tablica 2. Korelacijska tablica prou~avanih vrijednosti (podebljane su signifikantne za p < 0,05)

Characteristics

Zna~ajke

Means

Artimeti~kesredine

Std. Dev.

Standardnedevijacije

Enginepower

Snagamotora

Length

Duljina

Width

[irina

Height

Visina

Clearance

Odignutostvozila odpodloge

Mass

Masa

Payload

Nosivost

Cranereach

Dosegdizalice

Lifting moment(gross)

Bruto podiznimomentdizalice

Engine power, kW

Snaga motora, kW138.24 28.51 1.00 0.60 0.72 0.53 0.53 0.82 0.81 0.08 0.79

Length, mm

Duljina, mm9,314.38 874.15 0.60 1.00 0.63 0.32 0.60 0.66 0.67 –0.02 0.67

Width, mm

[irina, mm2,716.63 170.42 0.72 0.63 1.00 0.59 0.47 0.80 0.84 0.12 0.82

Height, mm

Visina, mm3,710.45 133.33 0.53 0.32 0.59 1.00 0.34 0.64 0.65 0.35 0.70

Clearance, mm

Odignutost vozila odpodloge, mm

637.36 57.64 0.53 0.60 0.47 0.34 1.00 0.58 0.60 –0.08 0.61

Mass, kg

Masa, kg15,183.75 3,038.63 0.82 0.66 0.80 0.64 0.58 1.00 0.85 0.11 0.84

Payload, kg

Nosivost, kg12,672.46 2,702.39 0.81 0.67 0.84 0.65 0.60 0.85 1.00 0.12 0.89

Crane reach, m

Doseg dizalice, m8.88 1.21 0.08 –0.02 0.12 0.35 –0.08 0.11 0.12 1.00 0.27

Lifting moment(gross), kN

Bruto podiznimoment dizalice, kN

107.10 24.42 0.79 0.67 0.82 0.70 0.61 0.84 0.89 0.27 1.00

4. Results of the research – Rezultatiistraìvanja

4.1 Forwarder classification – Razredbaforvardera

Forwarder analysis was carried out in the pro-gram package Statistica 08. In this analysis, the fol-lowing vehicle morphological values were used:length, width, height to the cab roof, clearance of thevehicle from the ground, mass, payload, reach andlifting moment of the hydraulic crane. For the valueswhose data were not available in the establisheddatabase, substitution was made with the value ofthe arithmetic mean of that variable. Database con-tains variables for 56 forwarders. Through a thoroughconsideration of the effect of available data on mor-phological characteristics of vehicles, the connectionof the vehicle mass with most other values is evident(Table 2), which is logical due to the fact that theexistence of mass determines the occurrence of otherfeatures. Vehicle mass is mostly correlated to thepower of the engine and to payload and it is the keyparameter, on which all other forwarder characte-ristics, except the hydraulic crane reach, are depen-dent. If the mass value increases, all other vehiclecharacteristics increase, too.

Payload (PL, load capacity) is one of the mostimportant exploitation characteristics of forwarders.By reviewing the vehicles’ technical characteristicsdatabase it can be determined that mass and loadcapacity of forwarders are approximately the same.The highest correlation to other values is indicatedprecisely by the PL of the vehicle (Table 2). For thisreason, PL was used for the classification of forwar-ders.

The k-mean algorithm was used for grouping offorwarders. This algorithm assigns each item to thegroup whose centroid is closest to it. Centroid is apoint created by calculating the arithmetic mean foreach dimension, separately for each item in thegroup. By implementing the mentioned algorithm,grouping of data into groups based on PL was made.The first group includes forwarders whose PL isclosest to the centroid of 9,929 kg. The second groupincludes those whose PL is closest to the centroidvalue of 12,125 kg, while the third group is formedby forwarders whose PL is closest to the value of15,571 kg. Distribution of variables, payload andother technical features according to forwarder classare shown in Fig. 3.

Through further analysis for the needs of ope-rative classification of forwarders, rough borderlinescan be set among three forwarder classes by their PL,and those are: 11,000 kg and 14,000 kg. The first class

consists of vehicles whose PL is less than 11,000 kg,the second of those whose PL amounts from 11,000to 14,000 kg, while the third class consists of forwar-ders whose PL is above 14,000 kg.

As it is obvious that the increase of PL in theforwarder family results in the increase of other stu-died dimensions, it can be concluded that there arethree forwarder classes – light, medium and heavyforwarders. In line with the performed classificationit can be determined that light forwarders are notused in the Croatian forestry. Therefore further re-search will be focused on the medium and heavyforwarders. Timberjack 1210 and Valmet 840 fall intothe class of medium forwarders, whereas Timberjack1410, Timberjack 1710 and Valmet 860 are in the classof heavy forwarders.

4.2 Characteristics of assortments and vehicleload – Zna~ajke sortimenata i tovaraforvardera

In order to gain insight into the load charac-teristics (mean volume and mean diameter), datafrom 1532 working sites were analysed, where tim-ber extraction was carried out by forwarders overthe last few years (since the beginning of full imple-mentation of information production subsystemHsPPI and HsPro). Work sites were situated in thearea of the Croatian lowland forests, and theyare characterized by motor-manual felling and as-sortment method of timber processing along withthe timber extraction by forwarders. Each point inFig. 4 represents average value for individual fellingsite.

Two groups of assortment size can be detected(Fig. 4). The first group is formed by the classes oflarge assortments of bigger dimensions – veneer logs,sawlogs (1st, 2nd and 3rd class) and logs for peeling.The second group includes small assortments, usu-ally of smaller dimensions – long firewood, miningwood and thin industrial roundwood. Both assort-ment groups show a large dissipation of raw data,which is a consequence of buck-to-quality (BTQ)and assortment method of timber processing.

Dependence of the number of loaded assortmentson the decrease of soil bearing capacity has beendetermined (Fig. 5). By decrease of soil bearingcapacity, the number of loaded roundwood assort-ments is reduced as well. In some cases, the overloadof forwarder was noticed in conditions of limitedsoil bearing capacity, aimed at increasing producti-vity in spite of the decrease of vehicle speed. This canbe explained by the subjective influence of someforwarder operators and their overloading of thevehicle in unfavourable conditions, all with the goalof increasing the work efficiency. Reduction of load-

Croat. j. for. eng. 33(2012)1 67


68 Croat. j. for. eng. 33(2012)1


Fig. 3 Some technical features according to forwarder classSlika 3. Neke tehni~ke zna~ajke pojedinih razreda forvardera

ed assortments in conditions of reduced soil bearingcapacity was more expressed with the large thanwith the medium size forwarders.

The analysis that was carried out, i.e. the mo-delling of the mean assortment volume, is the input

indicator for determining further load characteristics.One of the most important parameters is also thenumber of loaded assortments (Fig. 5). The product ofmean assortment volume and number of assortmentsgives the load volume (Vl = Va × n).

Croat. j. for. eng. 33(2012)1 69


Fig. 4 Characteristics of roundwood from Croatian lowland forestsSlika 4. Zna~ajke oblovine iz hrvatskih nizinskih {uma

Fig. 5 Number of roundwood pieces in the bunk area of forwarderSlika 5. Broj komada oblovine u tovarnom prostoru forvardera

4.3 Modeling of the forwarder productivityOblikovanje proizvodnosti forvardera

The forwarding productivity was studied usingthe time study on totally 1440 recorded work cycles,out of which 651 cycles were performed with me-dium, and 789 with heavy forwarders.

4.3.1 Time consumption of loaded and unloadedvehicle travel – Utro{ak vremena vo`njioptere}enoga i neoptere}enoga vozila

Based on the dependence of time on the traveldistance, the average speed of (un)loaded forward-ers on forest road and off-road was calculated. Theassumption was that forwarders move at uniformspeed (Fig. 6). Medium size forwarders have a bettermobility in the conditions of limited soil bearingcapacity than heavy forwarders when they areunloaded. This is not the case in the conditions ofgood soil bearing capacity where heavy forwardersreach higher speeds. Larger differences in the vehiclespeeds on the forest road between the forwarderclasses are caused by bigger variety of conditions onthe monitored sites in the areas of roadside landings.

Based on the modeled driving speeds (arithmeticmeans of recorded speeds per turn, Fig. 6) of for-

warders and average traveling distances off-road(sof) and on the forest road (son), time consumption ofa traveling is obtained.

4.3.2 Time consumption of timber loadingUtro{ak vremena utovara drva

Timber loading time covers the time of forward-er’s work in the felling area during loading, and thecharacteristic of this variable is that it does not changewith the change of the forwarding distance. For-warder’s work in the felling area starts with the endof the unloaded vehicle travel, or in other words, onthe spot of the first loading. After loading the pro-cessed assortments within the reach of the hydrauliccrane, the forwarder moves towards the next load-ing place, and continues doing so until reaching theoptimal load. During timber loading (tl), two signi-ficantly different groups of work components can bedetected (tl = tl1 + tl2):

Þ Timber loading with crane (tl1) – the operatorloads the timber into the bunk area using only thehydraulic crane,

Þ Relocation of forwarder (tl2) – forwarder movesfrom one loading area to the other.

70 Croat. j. for. eng. 33(2012)1


Fig. 6 Forwarders’ speedSlika 6. Brzine kretanja forvardera

Time consumption of timber loading by the hy-draulic crane is dependent on the forwarder classand the number of loaded assortments. The recordeddata are equalized by a linear model line from thesource (Fig. 7, left). Timber loading expressed theinfluence of the »Volume-Piece Law«, as the smallerdimensions of the loaded roundwood, the numberof loaded pieces and the crane time consumptionhave increased.

Time consumption of forwarder relocation is im-pacted by the »Production Law«, i.e. by the quantityof the cut and processed timber per unit of area(Fig. 7, right). It is reflected in the exponentialincrease of time consumption of forwarder reloca-tion due to diminished felling density (thinning) andvice versa (shelterwood and clear cutting). Reloca-tion time consumption is higher within the group ofheavy than medium forwarders. This is due to thefact that medium forwarders have larger hydrauliccrane reach than heavy forwarders (Table 1).

4.3.3 Time consumption of timber unloadingUtro{ak vremena istovara drva

When the loaded forwarder ends its travel, itswork starts on the roadside landing aimed at un-loading, stacking and sorting of timber. Similar tothe loading, the unloading at the roadside landing(tu) is additionally divided into two groups of workcomponents (tu = tu1 + tu2):Þ Crane work time (tu1, where the operator works

solely with the hydraulic crane with the goal ofunloading the timber), and

Þ Relocation time during unloading (tu2, where theforwarder moves from pile to pile with the goalof separating timber by tree species and qualityclasses).

Time consumption of crane unloading dependson the forwarder class and number of roundwood inthe load. During unloading, the operators classifythe timber according to tree species and quality class-es, piling the unloaded timber onto separate stacks.The regression curve of recorded data is shown inFig. 8. The asymptotic model was used. The increaseof time consumption of crane unloading with re-ference to the increase of number of loaded assort-ments can be observed. It is decreased with the larg-er number of loaded assortments of smaller meanvolume. This is explained by the fact that when un-loading, the crane grips two or more pieces of round-wood assortments.

The absence of wood classification and relocationhas been noticed on a smaller part of observed re-search sites. This was conditioned by the stand cha-racteristics (pure stands), silvicultural treatment (typeof cutting), type of processing firewood, quality anddimensions of assortments and landing space. In thecases when timber was sorted on the roadside landing,higher time consumption of this work componentwas recorded. Mean time consumption for heavyforwarders was 0.84 min/turn, whereas for mediumforwarders it amounted to 0.73 min/turn (Fig. 8,right). This phenomenon can be explained with thehigher initial acceleration of medium forwarders.

Croat. j. for. eng. 33(2012)1 71


Fig. 7 Time consumption of timber loadingSlika 7. Utro{ak vremena utovara drva

The sorting of assortments at the roadside landinghas affected the decrease of forwarder efficiency inrelation to its efficiency when not performing thetimber separation when unloading. By the increaseof forwarding distance, the negative effect of timberseparation on forwarding efficiency is diminished,due to the growth of vehicle relocating share in thetotal cycle time.

4.3.4 Delays (downtime) and additional timefactors – Prekidi rada i faktori dodatnogavremena

Delays consist of unavoidable and avoidable ofwork times. Various technological and organizatio-nal measures are taken to try and reduce it to thenecessary level. The unavoidable delays are classi-fied as preparatory time, occasional works and breaks.The avoidable delays include unnecessary conversa-tions among workers, conversations between workersand passers-by and recorders, and excessive restingtime. Vehicle breakdowns that cannot be eliminatedwithout the intervention of a mechanic are also includ-ed into the avoidable delays. Avoidable and unavoid-able delays per turn were taken into analysis toget-her and they are shown in Fig. 9 (left).

The additional time and additional time factorare determined through the analysis of unavoidabledelays only. It was determined by this study that theadditional time factors vary in a wide range and thatthey are higher than in previous studies. The aver-age additional time was determined for each indi-vidual OS (Fig. 9, right). The value of the mean

additional time factor amounts to 1.33, or 33% of theeffective time. Considering the structure of the addi-tional time, it can be determined that the preparatorytime accounts for 33%, occasional works for 33%,and personal breaks for 33% of the total unavoidabledelays.

5. Implementation of the model into theinformation system – Ugra|ivanje modela

u informacijski sustav

One of the components of production planningprocess is the determination of norms for felling andprocessing, as well as for timber extraction. The exist-ing norms (official and still in use) are inherited fromtimes before the company H[ was founded (before1990), and there are still a couple of regional systemsfunctioning.

In order to unify the norm system on the level ofthe company, »new norms« as a result of work of theForestry Faculty Zagreb (project bearer) and H[ (pro-ject investor) were created. New norms have beenintegrated into the HsPPI program (Fig. 10). Deter-mination of norms starts with the selection of themanagement unit (gospodarska jedinica) and type ofyield (vrsta prihoda), followed with the list of themarked compartments/subcompartments from theManagement Plan with all the data needed for normcalculation. Those are: type of yield (prihod), silvicul-tural form (uzgojni oblik) and total area of the compart-ment/subcompartment (povr{ina). For each compart-

72 Croat. j. for. eng. 33(2012)1


Fig. 8 Time consumption of timber unloadingSlika 8. Utro{ak vremena istovara drva

ment/subcompartment from the list there is normcalculated for individual work phase, and this ismade by selecting tabs: »Felling and Processing«(sje~a i izrada), »Extraction – Skidders« (privla~enje –

traktori) or »Extraction – Forwarders« (izvoènje –forvarderi).

The first step in the norm calculation process isthe calculation of felling and processing norm, due

Croat. j. for. eng. 33(2012)1 73


Fig. 9 Share of delays in relation to effective time and additional time factorSlika 9. Udjeli prekida rada prema efektivnomu vremenu i faktor dodatnoga vremena

Fig. 10 Screenshot of tab for norm calculation for forwarders in HsPPISlika 10. Prikaz zaslona ra~unala pri izra~unu normativa za forvardere u aplikaciji HsPPI

to the fact that by selecting the work method, the finalassortment structure is obtained, for whose extractionthe norm is to be developed. From other data neces-sary for the development of forwarding norms, a partis taken from the Felling Plan (main tree species –glavna vrsta; volume of mean stand tree – SKS; netmarked wood volume per unit of area – neto dozna-~eno), while other parameters are entered (Fig. 10):

Þ machine type (tip stroja),Þ equipped with semi-tracks (upotreba polugusjenica),Þ soil-bearing capacity (nosivost tla),Þ mean off-road forwarding distance (srednja uda-

ljenost kretanja vozila po bespu}u),Þ mean forwarding distance on roadside landing

(srednja udaljenost kretanja vozila po pomo}nom sto-vari{tu).Output data are norms for large (tehnika) and

small assortments (TO i VM) per hour and per work-day (8 hours) for selected work conditions.

Through a thorough analysis carried out by fo-restry experts it was established that the producti-vity model presented in this study plans highernorms and decreased delay times than the existingones (Tomi} 2007).

6. Conclusions – Zaklju~ci

This research covered the analysis of the factorsimpacting forwarding, as a special aspect of primarytransport of timber in the lowland forests of theRepublic of Croatia. It is characteristic of timberharvesting systems in the area that felling is perfor-med motor-manually and timber is processed bypower chainsaws, timber is bucked according to itsquality, and extraction of timber to roadside land-ings is fully mechanized. The method used is not thetraditional cut-to-length (CTL), but buck-to-quality(BTQ) method.

Aiming to develop an operationally implement-able system of timber forwarding planning, forwar-ders were classified according to their technical cha-racteristics. The most important factor appeared tobe the payload, so this variable was used for cluster-ing the vehicle types. Three classes of forwarderswere determined: light, medium and heavy forward-ers. Light forwarders have a load capacity of up to11,000 kg, medium from 11,000 kg to 14,000 kg, andheavy forwarders above 14,000 kg. Light forwardersare not used in the Croatian forestry, and farm trac-tors with semi-trailers equipped with winch andhydraulic crane are used instead.

Loaded roundwood features were determinedwith the goal of calculating productivity (norm pro-jection) by modeling the volume of large and small

assortments from an average marked tree volumefor all species represented in the lowland forests. Thedata were gathered by joining together two infor-mation subsystems HsPro and HsPPI. By the increaseof marked tree volume, the average volume of largeassortments grows exponentially, whereas with smallassortments, after the initial growth, the relationstake values closer to the asymptote of the curve(0.34 m3/pcs).

The results of the forwarding productivity studyare under a strong influence of the interaction ofimportant factors prevailing in the Croatian lowlandforests, and the study came to the following con-clusions:

Þ The forwarder class influences the level of for-warder productivity, and it does so primarilythrough its payload, or load volume, but alsothrough its speed and time consumption duringloading and unloading.

Þ Diminished levels of timber extraction by for-warders are influenced by conditions of off-roadsoil-bearing capacities as a result of the increaseof time consumption of forwarding, i.e. lowerspeed and lower load volume.

Þ The use of semi-tracks, which provide the mobi-lity of forwarders in unfavorable conditions, ad-ditionally lower the speed, increasing the timeconsumption of forwarding.

Þ The increase of forwarding distances diminishesforwarder’s productivity, as the share of the timespent moving grows within the structure of thetotal time consumption of the work shift. How-ever, the influence of distance on the forwardingproductivity should be viewed through its inter-action with the classes of soil-bearing capacityand classes of forwarders. Likewise, with the in-crease of forwarding distance, the load volumebecomes more significant.

Þ Stand conditions and forest management guide-lines demonstrated the impact on the producti-vity of timber forwarding through the well knownLaws of Mechanizing Forest Works, i.e. through fell-ing density (Productivity Law), features and di-mensions of processed roundwood (Volume-PieceLaw and Product Type Law).

Based on the obtained research results and requestsof the company H[, a model of forwarder productivi-ty for lowland forests was established and finally in-corporated into the production information subsys-tem. Real data from the first planning stage (forestinventory data, tree marking plan, assortment struc-ture plan, etc.) and developed forwarder productivitymodel, together with input work parameters ensuresthe objectivity of norms used in timber forwarding.

74 Croat. j. for. eng. 33(2012)1


Acknowledgements – Zahvala

The research was conducted with the support ofthe company »Hrvatske {ume« d.o.o. that providedthe financial support and insured the material andhuman resources for the execution of the project»Systematization of Norms for the Production of TimberAssortments – Norms for Forwarding«. The projectbearer was the Faculty of Forestry of the Universityof Zagreb.

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Saètak

Modeli proizvodnosti pri operativnom planiranju izvoènja drvaforvarderima u Hrvatskoj

U podru~ju hrvatskih nizinskih {uma za skupljanje i privla~enje drvnih sortimenata primjenjuje se posebanoblik primarnoga transporta drva, za koji je znakovita potpuna odignutost tereta (oblovine) od tla, pri ~emu sekoriste forvarderi. Forvarderi su samopogonjena vozila namijenjena pomicanju stabala ili njegovih dijelova kojidrvo izvoze utovareno u tovarnom prostoru vozila iz {umskoga bespu}a do pomo}noga stovari{ta, odnosno {umskeceste. U sklopu istraìva~koga projekta »Usustavljenje normi i normativa«, koji financiraju Hrvatske {ume d.o.o.,razvijene su nove proizvodne norme izvoènja drva forvarderima.

Proizvodnost izvoènja drva ovisi o kori{tenom tipu vozila. Stoga je za provedbu istraìvanja bilo potrebno pri-kupiti podatke o tehni~kim zna~ajkama novijih forvardera u Republici Hrvatskoj, ali i u svijetu. Potom se pristupilomorfolo{koj ra{~lambi na osnovi koje su se vozila razvrstala u razrede, jer je neodrìvo projektirati normu za svakitip vozila zasebno. Klasterskom analizom dobivena su tri razreda forvardera. To su laki, srednje te{ki i te{ki forvar-deri. Kao najva`niji ~imbenik pri razvrstavanju pokazala se nosivost forvardera. Laki su nosivosti do 11 t, srednjete{ki od 11 do 14, a te{ki forvarderi imaju nosivost ve}u od 14 t. U hrvatskom {umarstvu koriste se uglavnomsrednje te{ki i te{ki forvarderi, dok se umjesto lakih forvardera koriste razne ina~ice traktorskih ekipaà.

Primjena izvoènja drva razumijeva sortimentnu metodu izradbe oblovine. Stoga su zna~ajke tovara (pro-sje~an obujam komada i njegove dimenzije) posredno uvjetovane i prosje~nim dimenzijama dozna~enih stabala zasje~u i izradbu. Spojeni su podaci iz dviju aplikacija (HsPPI i HsPRO) za ona radili{ta na kojima se od po~etka pri-mjene tih aplikacija izvozilo forvarderima. Na osnovi podataka o doznaci stabala oblikovane su zna~ajke oblovine uetatu najzastupljenijih vrsta drva.

Informati~ka slu`ba poduze}a Hrvatske {ume d.o.o. preuzela je zadatak izrade sustava za prikupljanje i pohra-nu snimljenih podataka. Za pohranu se koristila baza podataka MS SQL Server 2000. Kao korisni~ko su~elje za prih-vat podataka sluìla je web-aplikacija zasnovana na dinami~nim mre`nim stranicama koje se u potpunosti izvr{a-vaju na posluìteljskom ra~unalu i izravno komuniciraju s bazom podataka. Sustav je izra|en pomo}u tehnologijeMicrosoft ASP.NET, programiran u Visual Basic.NET-u, a izvr{ava se na posluìtelju Windows Server 2003.

Rad je forvardera istraèn na 22 radili{ta metodama studija rada i vremena, primjenom povratne metodekronometrije. Radi {to korektnijega oblikovanja utro{aka vremena tim su podacima pridruèni i podaci prethodnihistraìvanja, opsega 8 radili{ta, te je oblikovanje utro{aka vremena rada zasnovano na podacima s ukupno 30 radi-li{ta. Pri ra{~lambi su upotrijebljeni prikupljeni podaci o sastojinskim i terenskim utjecajnim ~imbenicima izvo-ènja drva.

Pri planiranju privla~enja drva, kao najzahtjevnijoj sastavnici pridobivanja drva, postavljaju se zahtjevi zapoznavanjem prisutnih utjecajnih ~imbenika odre|enoga podru~ja te njihova djelovanja na djelotvornost kori-{tenih sredstava privla~enja drva. Va`niji utjecajni ~imbenici izvoènja drva iz sje~ina hrvatskih nizinskih {umanastali iz ovoga istraìvanja svakako su srednja udaljenost privla~enja, nosivost podloge (tla), obujam prosje~nogakomada oblovine u tovaru, sje~na gusto}a te nosivost forvardera. Regresijskom ra{~lambom utvr|ena je ovisnosttrajanja pojedinih sastavnica rada o utjecajnim ~imbenicima te je izra|en model proizvodnosti forvardera.

Po zavr{etku istraìvanja dobiveni je model prema zahtjevima naru~itelja ugra|en u program HsPPi. Tu jeaplikaciju razvila Informati~ka slu`ba poduze}a Hrvatske {ume d.o.o., a koristi se za planiranje proizvodnje.Glavni su dijelovi sustava za pripremu proizvodnje: priprema doznake, plan sje~a, plan proizvodnje i plan prodaje.

Croat. j. for. eng. 33(2012)1 77


Unutar dijela za izradu plana proizvodnje nalazi se i modul za izra~un normativa izvoènja drva forvarderima.Ovdje razvijen i opisan sustav za planiranje normativa izvoènja drva forvarderima uskoro zapo~inje s operativ-nom primjenom u hrvatskom dràvnom {umarstvu.

Klju~ne rije~i: forvarder, norme proizvodnosti, planiranje, nizinske {ume, Hrvatska

78 Croat. j. for. eng. 33(2012)1


Received (Primljeno): September 25, 2011Accepted (Prihva}eno): May 22, 2012

Authors’ addresses – Adresa autorâ:

Igor Stanki}, PhDe-mail: [email protected]. Prof. Tomislav Por{insky, PhDe-mail: [email protected] of forest engineeringForestry Faculty, University of ZagrebSveto{imunska 25, HR-10000 ZagrebCROATIA

@eljko Toma{i}, PhDe-mail: [email protected] Tonkovi}, dipl. ing.e-mail: [email protected] Frnti}, dipl. ing.e-mail: [email protected] {ume d.o.o. (Croatian forests LLC)DirectorateVukotinovi}eva 2, HR-10000 ZagrebCROATIA

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