The diminishing loop counterbalance (DLC)

Transcription

1 Thomas Evans

2 The diminishing loop counterbalance (DLC) Not my idea Taught to me by others Someone else deserves the credit It is brilliant I am sharing it to help others

3 Introduction/Overview Required Conditions Rigging DLC and Belays The Edge Transition The Physics Final Thoughts

4 DLC is Light rigging Requires little gear Single rescuer Fast Efficient Simple Easy to use

5 Single patient and rescuer With or without litter

6 This is an introduction The paper is a study guide Use it with practice Do not trust me, try it!

7 Rigging: Pulley, rope, carabiner One patient Attached to rope With or without a litter One rescuer Climbs other end of rope Tethered to patient MA= 2:1

8 Rig for a free hang Friction reduces efficiency Friction can stop the system If not possible Try something else

9 Have enough rope Twice pitch length If not available Standard haul Standard counterbalance

10 Rescuer has solid SRT skills Climb Rappel Change from climb to rappel Change from rappel to climb Cross knots going up and down Switch ropes mid air Use ascenders! Efficient climbing system

11 Anchor for 2 person load Pulley and carabiner Rope, both ends at bottom Free hang! Attach patient to rope Tether rescuer to patient Rescuer climbs Patient can help (if able)!

12 Tethers Rope tail Cows tail Webbing Etc. Length situation dependant

13 Short Close for monitoring/maneuvering Long Ease of climbing Can change length Must have a connection at all times

14 PMP and prusik No longer lower patient No PCD facilitate maneuvers Easy change from raise to lower Progress capture Not necessary Often detrimental Situation dependent

15 Easy to escape load Change over If 2 ropes are needed Place knot in climbers side Climber crosses the knot On rope maneuvers easy Climber feels ½ difference in mass

16 Backup Often used uncritically Belays can cause problems too Balance between good and bad Consider the following:

17 Pro s Equipment failure Potential for anchor failure Human error Con s Potential for rope twist Potential for rock fall

18 Equipment failure A belay prevents dire consequences Exceedingly rare event Gear does not spontaneously fail In free hang No forces on DLC Failure vanishingly rare Against a wall Seriously consider a belay

19 Potential anchor failure Two person load More if patient catches on walls Belay solves this problem Better solutions are Build a better anchor (bombproof) Backup main anchor

20 Human error Always possible Use belays in training Use belays when: Do not hinder system operation Cause unacceptable rockfall risk

21 Potential for rope twist Twist can stop system function Belays may compound twist hazard Twist risk increases with Longer pitches Ropes hang close together In turbulent air (near waterfalls)

22 Mitigation Rig DLC with two upper anchors Anchors experience higher forces though Tag Lines Do not work for long drops No belay Common for cave rescuers Opt out to ensure system function

23 Potential for rockfall Moving ropes facilitate rockfall DLC moving parts over edge Adding a belay Adds a moving rope over lip Increases rockfall hazard If rockfall is a problem A belay may be detrimental

24 Situation dependant Weigh pro s and con s Equipment/gear/human failure Rope twist/rockfall Use when pro s outweigh con s

25 Belay appropriate for 2 people Attach to patient Improved rescuer maneuverability But, rescuer can fall Up to twice the tether length If belay desired at lip Clip to patient before edge transition

26 DLC is an effective small party tool Often used without a belay Limited equipment Limited personnel Belay use covered by protocols

27 DLC creates an edge problem Raises patient to edge, not over it Two solutions presented here Rig to a high anchor A second counterbalance system There are many other options!

28 Rig to a high anchor Patient clears lip in free hang Patient pulled over lip by A tag line A second haul system

29 Rig to a high anchor Add a releasable anchor Makes a smoother transition Locked off munter Locked off rack RLRH Etc.

30 A second counterbalance system Build a DLC Build a piggyback 2:1 With internal progress capture Required!!!! With change of direction Drape second tail over lip Long tail Enough to transfer to

31 Tips Place pulleys at lip Not over it Rope stretch pulls them over Carabiner gate UP! Pulled over lip twice Or use a screw link Pad the lip

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33 Notes Second system is 2:1 when tether slack Second system is 3:1 when tether tight More MA to overcome lip At lip Grasp carabiner and pull out and up Rock patient back and forth Patient can assist (if able)

34 System recap A DLC hung from another system A 2:1 when tether slack A 3:1 when tether taught Look at geometry

35 Credit where credit is due John Punches Anmar Mirza National Cave Rescue Commission Instructors The have championed this system

36 This is tricky Conservation of work Work = Force X Distance Work stays constant Distance doubled Force cut in half MA = 2:1

37 This elegance Two strands of rope Each take half the load Climber experiences: If lighter: +½ difference in mass Harder to climb If heavier: -½ difference in mass Easier to climb!!

38 The consequence On rope maneuvers easy! Changeovers Moving the patient The patient can help (if able)!

39 DLC Simple Easy Fast Efficient One person Little equipment

40 Elegant solution When conditions are favorable Excellent small party rigging tool Useful for call out rescues too Try it out! This is one of many options!

41 My instructors John Punches Aaron Stavens They corrected Content Grammar They added content Improved the philosophy Sarah Truebe Extensive editing

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