Disclaimer: The views and opinions expressed in this article are those of the author and do not necessarily reflect the views of the Arboricultural Association.

Share this story


#ARBatwork #ArbMatters #PledgeLessPlastic & 12 Faces of Arb 1987 storm 2 Rope 2018 30 Under 30 3ATC 3ATC UK Open 50th annual AA AA award AA Awards Aboricultural Association Accident accreditation advice AFL aftercare AGM Agrilus Biguttatus aid air quality Alert Alex Kirkley All Party Parliamentary Group on Horticulture amenity Amenity Conference Anatomy Ancient Tree Forum Annual Awards APF APF 2020 app APPGHG application Appointment apprentice apprenticeship Apprenticeships Approved Approved Contractor Approved Contractors ARB ARB Approved Contractor ARB Approved Contractors ARB at work ARB Magazine ARB Show arb training ArbAC ARBatwork ArbCamp Arbor Day Arboricultural Association Arboriculture arborists Arbsafe Ash Ash Archive ash dieback Asian Hornet Assessments atf ATO Australia Autumn Review award Awards Barcham Trees Bark Beetle Bartlett Bartlett Tree Experts bats beetle beyond ism Bill Matthews biochar biodiversity biomechanical biosecurity Book Prize Book Shop Books Bookshop boundaries branch Branches brand Brexit bs5837 Budgeting Tool bursary business Call for Abrstacts Call for papers Campout Canker stain of plane carbon career Cavanagh CCS Cellular Confinement Cellular Confinement Systems CEnv CEO Ceratocystis Ceratocystis platani chainsaw chalara charity Charles charter Charter for Trees Chartered Environmentalist chelsea Chelsea Flower Show Claus Mattheck climate climate change climber climbing Cofor Colleges committees competition competiton conference Confor conifers conservation Consultant consultation Continuous Professional Development Contractor Contractors Cornwall Cornwall Branch Coronavirus Coroner Council Countryside Countryside Code Countryside Stewardship Course for beginners COVID-19 CPD cross industry news Crown & Canopy Cryphonectria parasitica Cumbria DART Date for your diary deadwood death debate Debt defra Design Devon Director disease diversity document donate dothistroma downloads draft Dutch elm EAC East Anglia ecology Economic Report economy Ecotricity education EFUF Election elections Electricity Elm yellows Emerald Ash Borer England England Tree Strategy English Elm environment environmental EPF equipment Europe European Arboricultural Council European Forum on Urban Forestry European Wood Pastures Event exeter Exhibitors Fall from Height Fatal Fatality felling Fellow Fellow Members Fera Field Trip Finance Fine firewood First Aid flood flooding for Forest Research forestry Forestry Commission forests freelancers FSC Fund4Trees funding fundraiser fungal fungi Future Flora Futurebuild gardening GDPR Geocells Gold Medal Gov.uk government grant grants Green Brexit Green Infrastructure Green Infratructure Guarantee guidance Guidance Note Guidance Note 2 guide guides Hazard Tree Health heart-rot hedges Helliwell Help Henry Girling Henry Kuppen History HMRC HOMED Homeworking Honey Brothers honours Horse Chestnut HortAid horticulture horticulturists HortWeek housing HRH HRH Prince Charles HS2 HSE HTA ICF ICoP identification Immigration import industry Industry Code of Practice industry skills Infographic InfraGreen Initiatives Inspiration Insurance Intermediate Tree Inspection International Urban Forestry Congress International Women’s Day International Year of Plant Health Investigating Tree Archaeology Conference Ips typographus Irma irrigation ISA iso i-Tree IUFC IWD21 Job job opportunity judgement JustGiving Karabiner Kew Kit land-based Landsaping Landscape Institute Landscape Show landscaping Lantra law Leaf Minor Lectures legal legislation Letters Liability licence London longevity LTOA Magazine manifesto maple Mayor of London MBE Melbourne Member Benefit Membership mentor Midlands moth' motion Myerscough NASA National Geographic National Tree Safety Group National Tree Week NATO Natural England NatureScot Netherlands New Year’s Honours News NHS nominations Northern Northumberland Notice notification NTIS NTOA NTOC NTSG Nurseries oak 'oak Oak Processionary Moth Oak-boring Beetle obituary Observatree occupation online opm Padua Papua parks parliament Perennial Pests & Diseases Pests and Diseases petition photo Phytophthora planning Planning Law Plant Health planting Plantsman Pledge Plumpton College policy poll Poster Power PPE Preston Twins Prince Charles Prince of Wales processionary Product Recall Professional Members prosecution Protect and Survive protected tree protection Qualifications Quotatis ramorum RC Reg Harris Registered Registered Consultant Registered Consultants Rememberance Day renewal REnvP Report Rescue research Research grant Resilience response results retrenchment review RFS rhs RHS Chelsea Flower Show Ride for Research Ride4Research rigging Rodney Helliwell rogue tree surgeons Royal Forestry Society RSFS Safe Working Practice Safety Safety Bulletin Safety Guides Saftey Sale school Scotland Scotland Branch Scottish Branch SDG Accord security seminars Share Sheffield Show Sierra Leone Site Guidance skills skills survey SocEnv soil soils South East South West SRT SRWP staff Standards statement Stationary Rope Stationary Rope Technique statutory STIHL strategy student Student Book Prize Student Conference Study Trip Sub-contractors Supporter survey Sustainable Soils Alliance Sweet Chestnut sweet chestnut blight symposium T Level T Levels Tatarian maple TDAG technical guide Technical Guides Technical Officers Technical Team Technician Members Technology Ted Green tender Thames & Chiltern The Arboricultural Association The Woodland Trust Thinking Arbs Thinking Arbs Day Timbersports Tony Kirkham Tools top-handled chainsaws,Elcoat, TPBE4 TPO Trading Standards trailblazer training transport Tree Tree Care Tree Champion Tree Council Tree Fayre Tree Health Tree Health Week Tree Inspection tree loss tree management Tree of the year Tree Officer Tree officers tree planning Tree Planting Tree Protection tree register tree species Tree Supply Tree Surgeon Tree Surgeons Tree Week Tree Work at Height Tree Workers Zone Treeconomics tree-felling TreeRadar trees trees' Trees & Society Trees, People and the Built Environment trust' trustee Trustees TrustMark Two Rope two-rope UAG Uitlity UK favourite ukas UKWAS urban urban forest Urban Forestry Urban Tree Challenge Fund Urban Tree Cover Urban Tree World Cup urban trees Utility Arboriculture Group UTWC vacancy VETcert veteran trees video Videos Virtual ARB Show volunteer voting VTA WAC Wales Warning Watering watering solutions Webinar webinars website Western Westonbirt Wharton White Paper WIA Witley Women Women in Arb women in arboriculture woodland Woodland Carbon Code Woodland Carbon Guarantee woodland trust woods Workshops World Environment Day Xylella young young arborists Young People’s Breakfast Event zoo

A simple rule of thumb for rigging forces from full-size tests

Author:  Andreas Detter
Last Updated:  14/08/2018
Lifting and resetting the test mass. The climber and mass were anchored with two fully independent systems. (Photo: Treemagineers Ltd)

Lifting and resetting the test mass. The climber and mass were anchored with two fully independent systems. (Photo: Treemagineers Ltd)

In the course of the Health and Safety Executive Rigging Research, studies on rigging forces have been conducted by blocking the friction device and measuring forces in the block at the rigging point during simulated drops.

The recorded peak forces did not act parallel to the trunk but on average at an angle of 30° to 40° to the trunk axis. This creates a lateral bending moment that may cause a stem used as an anchor point to fail. The forces that occur at the rigging point (i.e. the block) exceeded the weight of the lowered section by an average of 8 to 12 times, and this factor decreases with increasing mass (HSE Rigging Report 2008). In more recent drop tests with Teufelberger Ropes, the Treemagineers used logs with a mass of up to 750kg, which is three times the mass of the biggest sections used in previous tests (Donzelli et al., 1998; HSE Rigging Report, 2008; Kane et al., 2009).

Snatching one of the medium-size test masses. All drops were static. The piece was tied off on the lowering device at the base of the tree. (Photo: Treemagineers Ltd)

Snatching one of the medium-size test masses. All drops were static. The piece was tied off on the lowering device at the base of the tree. (Photo: Treemagineers Ltd)

The calculation of the forces that may occur at the anchor point during rigging operations is very complex, since numerous factors interact, and directly or indirectly affect the result. In addition to the mass of the lowered section, for example, the properties and length of the rope used also play an important role. For the experiments that are evaluated in Figure 1, only two types of rigging rope (double braid and kernmantle type) with 12mm and 14mm diameter were used. For those rigging systems, a rule of thumb for estimating the peak force in a worst-case scenario was derived.

According to this rule, the force peak on the pulley can be assumed to be 8 times the mass of the trunk plus 500kp (kilopond [kp] is a force unit equal to the weight of 1kg). The load on the short end of the rope connected to the dropped section (lead of the line) can be estimated by dividing this value by 1.8 (HSE Rigging Report 2008). This rule is of course a simplification, but it underestimated the peak forces for trunk sections by less than 10% in 22 drops where the friction device was blocked. On the other hand, the result was only by a quarter too high at max in this series of tests.

The estimates by this rule of thumb should not be readily applied to other rigging scenarios and different kinds of rope. For example, the use of more rigid ropes with higher strength or other braiding may lead to greater peak forces. Other tests show that when lowering crown sections that are still in leaf, even with a locked friction device, peak forces do not exceed the forces generated during the slow ‘dynamic’ deceleration of trunk sections with similar mass. These relationships are further explained in Chapter 8 of the HSE Rigging Report.

Figure 1: Evaluation of forces generated at the rigging point (block) during 22 topping-down operations of trunk sections with locked friction device. Data on P. sitchensis courtesy of Treemagineers and Teufelberger Ropes; other data from the HSE Rigging Report.

Figure 1: Evaluation of forces generated at the rigging point (block) during 22 topping-down operations of trunk sections with locked friction device. Data on P. sitchensis courtesy of Treemagineers and Teufelberger Ropes; other data from the HSE Rigging Report.

Unfortunately, studies where a forcemeter is placed between the pulley and the anchor sling at the rigging point may be misleading (e.g. Donzelli et al., 1998; Kane et al., 2009). With this setup, the actual distance of fall is significantly extended, and much greater forces will be recorded than in real tree care operations. In the meantime, however, a load sensor has been developed by Straightpoint in cooperation with the Treemagineers, which is integrated into a rigging block and thus enables unadulterated measurements of the forces during rigging operations.

The rule of thumb is displayed as the dashed line; the solid line indicates the average correlation between mass of section and generated peak force at the rigging point. The R2 value of this trend (least squares method) is close to 0.97 which qualifies the mass of the log as a very good indicator of the peak force (cf. Kane et al., 2009). Yet, using different ropes, setting up different rigging systems with reduced rope length or performing different rigging operations may alter the actual forces significantly. Therefore, the rule of thumb can only be applied by with caution and must be adapted to the actual situation by an experienced and competent person.

Andreas Detter holds an engineering degree in landscape architecture and works as a consultant, researcher and trainer at Brudi & Partner TreeConsult, Germany. He was the primary author of the HSE Rigging Report (2008), and he is still involved in research projects that aim at increasing work safety for arborists during climbing and rigging. He frequently teaches and publishes in the fields of tree biomechanics, basics of the pulling test method, ancient and habitat tree management and cabling of tree crowns.


Detter, A., Cowell, C., McKeown, L., Howard, P. 2008. Evaluation of Current Rigging and Dismantling Practices Used in Arboriculture (Research Report No. RR668), HSE Books. Health and Safety Executive, Norwich, UK. www.hse.gov.uk/research/rrpdf/rr668.pdf.

Donzelli, P.S., Palmer, K., Tompkins, R., Longstaff, S. 1998. ‘Dynamic Forces of Rigging Operations in the Tree Care Industry’. Poster.

Kane, B., Brena, S., Autio, W. 2009. ‘Forces and stresses generated during rigging operations’. Arboriculture & Urban Forestry 35: 68–74.

Schwenteck, G. 2014. ‘Dynamic Loading of Rigging Ropes under Practical Conditions’ (Diploma thesis). Technical University Dresden, Germany.

Article taken from Issue 182 of the ARB Magazine.