HELLMANS Logging Equipment for Horse Traction
Test report SmP 2015-2
by Paul Schmit of Tuntange, Luxembourg and Albano Moscardo of Verona, Italy www.schaffmatpaerd.org email@example.com
By a comparison test in Swedish forest, different horse drawn logging equipment, manufactured by HELLMANS from HERRLJUNGA (SWEDEN), was analyzed.
The trials, which took place in August 2015, showed that lifting the log from the ground, either at the front and/or at the rear, by adapted equipment during the logging, has great benefits concerning the required tractive effort of the horse.
Furthermore, it was found that wheeled equipment can be extremely advantageous, this not just for increasing the efficiency of the logging operation, but also for the horse’s comfort at work.
All tested equipment proved to be of sufficient strength to support the high loads in forestry use, while being at the same time lightweight enough for easy maneuverings in the forest.
In order to eliminate uneven loads and peak stresses, articulated hitch devices, following the alternate movement of the horse’s shoulders, should be given preference over rigid shaft assemblies.
Further information about a horse’s acceptable draft power can be found at www.schaffmatpaerd.org.
Over centuries, in many European regions, horse-logging operations followed old traditions, and are still doing this today. In Central Europe, skidding logs on the ground by a simple singletree is a common practice.
Traditionally, Swedish horse loggers used wooden sleighs. This changed in the fifties, when extracting timber was not just limited to the winter months, with the large forest areas covered for months with snow. Today, Sweden is a pioneer in horse logging equipment and there exists a wide range of horse drawn tools offered by five companies, that manufacture it beside other professional activities. Most equipment is nowadays made in steel and often hotgalvanized, assuring a long operational life under rough forest use.
Another distinctive feature of the draft horse use in Scandinavian countries is the hitch system. In general, the traces are not drawn out to a singletree, but consist only of small tug straps, which connect the hames to a central tug ring between the pack pad and the belly band. In this ring is inserted a draft bar made of flat iron with a slot and a safety pin, which allows one to fix shafts on both sides of the harness. Herein, the shafts have a triple function. Besides the transmission of the tractive and steering forces, they also allow to brake the load, a not to be underestimated safety aspect.
Traditionally, these shafts have been rigid and made of timber. The simplest and most economic solution for people working in the forest. However, research done in 2016 and 2017 by SmP at the SWEDISH ARMY MUSEUM in STOCKHOLM (SWEDEN) and in the NORDIC MUSEUM at JULITA GÅRD (SWEDEN) led to the conclusion that articulated shafts have been in use beginning at the end of the 19th century. Mainly for team hitches in forest or farm use, non-rigid shaft assemblies were offered alongside rigid shafts by major Swedish wagon manufacturers as standard equipment around 1920. Today however, rigid shafts still can be found on modern forest equipment, especially on arch skidders.
When the horse walks, its shoulders perform alternate backward and forward movements. The Scandinavian style shafts, being directly connected to the collar via the front tug straps and with the collar resting on the shoulders, can follow these movements, when being articulated along a vertical axis, allowing a longitudinal movement of both shaft sides.
Therefore, within the trials for the present report, the influence of rigid vs. articulated shafts on the shoulder strain has also been examined. This by a comparison of the left and right side forces in the harness.
One of the goals of the non-profit association Schaff mat Päerd is, beside its own prototype development and manufacturing, to support other equipment manufacturers through the testing of their products and publishing related studies.
The present test report covers the standard logging equipment offered by HELLMANS from HERRLJUNGA (SWEDEN). Besides training courses for working with draft horses, HELLMANS offers services with horses in various domains and manufactures standard as well as customized solutions for horse drawn equipment. Further information about their product range can be found at www.backagard.net.
Technical characteristics of the equipment:
Singletree – 800 mm
Log grapple – 305 mm (max. opening 65 mm)
Skid shafts – 1000 mm
Arch skidder – 950 mm
Wheeled pole arch – 1250 mm
4-wheel forwarder – 1330 mm
Singletree – 50 mm
Log grapple – 1300 mm (including chain)
Skid shafts – 2200 mm
Arch skidder – 2700 mm
Wheeled pole arch – 1450 mm
4-wheel forwarder – 5800 mm (including shafts)
Singletree – 30 mm
Log grapple – 305 mm
Skid shafts – 360 mm
Arch skidder – 850 mm
Wheeled pole arch – 900 mm
4-wheel forwarder – 1400 mm
Singletree – 2,9 kg
Log grapple – 10,4 kg
Skid shafts – 20,5 kg
Arch skidder – 30,0 kg
Wheeled pole arch – 62,0 kg
4-wheel forwarder – 230 kg
Log in the test:
Diameter: front 360 mm / rear 280 mm
Length: 3300 mm
Weight: 221 kg
Horse in the test:
Breed: Swedish Ardennes
Date of birth: 01.06.1998
Height: 1,62 m
Weight: 900 kg
Collar size: 25” half sweeny
Materials and methods
The measuring tests took place in a forest adjacent to the BÄCKAGÅRD farm of the HELLMAN family in HERRLJUNGA (SWEDEN) on 14.08.15.
In order to evaluate the required tractive effort of each piece of equipment, the draft forces were measured on five different test sections A to E with the following ground conditions and lengths:
A forest track flat 15 m
B forest track uphill 49 m with 9,25 % pitch
C forest flat 53 m
D forest uphill 25 m with 13 % pitch followed by forest flat 12 m
E forest downhill 17 m with 15 % pitch
All measurements were made between 10.30 – 12.30 and 13.30 – 15.00 o’clock. This relatively long test duration was due to the breaks, in which the next piece of equipment to be tested was prepared in the forest and the horse was driven to its stable at the farm for resting. This allowed that all tests were done under nearly the same conditions.
The measuring device consisted of the following components:
– two Lorenz K-100 force sensors mounted between the leather front tug straps and the central tug rings on both sides of the harness
– an AHLBORN Almemo 2690-8 data logger with memory connector and micro SD card saddled on the back pad of the harness
The mounting of the draft force sensors in the front tug straps and the saddled data logger allowed for the change of the whole measuring device from one equipment to the next without any adaptation.
In order to assure the best working comfort of the test horse, the collar, collar pad, back pad and breeching were the horse’s own harness parts. SmP supplied the adjustable wooden “Lone Star” hames, the front tug straps with measuring device as well as the leather traces, the latter in use for the trials with the singletree.
The total draft force, represented in the following graphs, is a calculation. Preliminary tests of the measuring equipment on the SCHMIT-LAROCHE farm in TUNTANGE (LUXEMBOURG), performed on 06.04.15, and the corresponding data analyzing showed that the adding up of both single values of the left/right side draft forces is of adequate accuracy for the present considerations.
The measured values were recorded with a summary-measuring rate of 100 Hz resulting in a frequency of 33 Hz for each of the three dimensions (time, left side draft force and right side draft force).
According to the expectations, a comparison of the test sections A and C in the graphs 1 to 7 shows that the overgrown forest ground requires more draft force than the forest track, on average + 25 %.
The summary graph 9 not just points out the influence of the different equipment, but also of the ground conditions and slopes. As expected, the highest tractive effort for all tested equipment is required on the steep uphill part of test section D. However, the downhill test section E, at the end of the test circuit back to the starting point, doesn’t stand out from the measured values. It is, for most of the tested equipment, on the same level as the flat forest path of the test section A. This underlines again the influence of the ground conditions. The same is true for the test sections B and C, requiring nearly the same expenditure of force for all tested equipment.
Another trait to be highlighted can be found by comparison of the graphs 1 and 2. Considering just the summary graph 9 would lead to the conclusion that the singletree with log grapple, known as “Domänsax” in Sweden, requires the same tractive effort as the skid shafts. However, the two above mentioned graphs show clearly the shock-absorbing effect of the full-length leather traces connected to the singletree. Graph 2, related to the steel skid shafts, shows significantly higher draft force peaks, exceeding even 6 kN, which corresponds to a total impact load on the harness and by that also to both shoulders of 621 kg. Even in millisecond range, this strain is not to be neglected, especially as it can be assumed that the short nylon-reinforced front tug straps have a limited absorbing capacity.
By comparison of graph 2 to all other graphs, it can be concluded that the steel skid shafts, dragging the log on the ground and transmitting the impact forces almost undamped, is the most inefficient and uncomfortable way of working for the horse.
Even having steel shafts, the arch skidder, represented in graphs 3 and 4 shows significantly better characteristics than the single tree with log grapple or the skid shafts. This logging tool not only requires a smaller draft effort by the horse, but also offers smoother motion sequences. This can be explained by the fact that the front end of the log is slightly lifted from the ground creating less shock loads and lower friction forces.
Graphs 4, 5 and 6, relating to the trials made with the wheeled pole arch, lifting the rear end of the log, point out the advantageous influence of this logging tool. In all three combinations, with the log grapple connected to the singletree, with the skid shafts and with the arch skidder, the load of the horse can be reduced considerably. A fact which also clearly emerges from the summary graphs 8 and 9. Within this context, it is not surprising that the combination of the two arch type logging tools at the front and the rear end of the log offers the best results of the skidding tools. This despite the fact, noticed during the trials, that the log tends to swing back and forward in the arch skidder because of the low friction coefficient of the wheels at the rear.
In spite of its high own tare weight, listed in the technical data above, the 4-wheel forwarder can be rated best. Represented in graph 7 and in comparison to the other logging equipment, this basic wheeled forwarder, known as “Fössing” in Sweden, comes up with the lowest total draft force average values and peaks within this test series. This thanks to the low rolling friction and the suspension characteristics of the pneumatic wheels. Furthermore the log, as being completely contactless with the ground and tightly fixed to the forwarder’s frame, didn’t interfere anymore in the motion sequences of the hitch.
Following the graph 7, the 4-wheel forwarder allows to reduce the draft force peaks to 50% and the average draft force requirements to 11 … 45 % of the singletree / log grapple combination. In simplified terms, the horse has to pull with the wheeled forwarder half as hard as in the ground skidding method.
Summary graph 8 clearly points out that, for nearly all the test sequences, the left side shoulder of the horse was subjected to more physical stress than the right side. Therefore, beside examining the average draft force requirements of the different logging tools, another main test content was the analysis of the left/ right side draft forces on each piece of equipment and especially the influence of articulated vs. rigid shafts on the shoulder pressure.
As explained above, the arch skidder helps reduce the draft force needed to pull the log, by lifting the log’s front end. However, as can be seen in the summary graph 8, the highest imbalance between the left and right side draft force have been measured on this tool, either alone or in combination with the wheeled pole arch. This can be explained by the rigid frame construction, which cannot follow the alternating forward movement sequences of both shoulders of the horse.
This correlation is also visible in graphs 3 and 4 where the green curve, related to the left side, is more pronounced and oscillating than the yellow line, related to the right side.
All tested equipment proved to be of sufficient strength to support the high loads in forestry use, while being at the same time lightweight enough for easy maneuverings in the forest. No failures, like bent parts or cracked welds, have been noticed during or after the tests.
All tested equipment can be recommended for forest use, however skid shafts or log grapples connected to a singletree mainly for smaller loads due to their unfavorable motion characteristics.
Wheeled forwarders, either in 4-, 6- or 8-wheel configuration, are popular tools among Swedish horse loggers. The present test report highlights the technical superiority of this equipment compared to the tools sliding on the ground.
Related to the issue of animal welfare, the importance of shock absorption should be addressed when working with non-lifted logs and steel shafts.
Furthermore, following the present test values, articulated shafts should be given preference and should become the standard in the future on all equipment, not just for forest, but also for farm use. In particular for a better working comfort of the horse.
In additional tests, the different wheeled forwarders, actually on the market, should be examined in order to compare their characteristics and for confirming the conclusions of this test report.