Alpine butterfly

[dgcunningham]

In the HSE Evaluation of Current Rigging and Dismantling Practices Used In Arboriculture: Prepared by Treevolution & Bruni et al 2008.

 

http://www.treevolution.co.uk/images/pdf/rr668.pdf

 

The Alpine Butterfly performed the worst in a series of 3 rigging tests resulting in a strength loss between 52-55% when compared to anchor hitch, buntline hitch, double fishermans and triple bowline. Table 7.7 pg. 173

 

Previously this reduction was considered to be in the region of 25- 39% (28-39% Lyon 2001) (25% Allaboutknots 2005)

[Dilz]

hmm interesting stuff, had a rope access worker over here in Sweden say the alpine butterfly reduced strength by up to 60% which has made me reconsider the system I use for setting up and advantage for pulling trees over, though with out having the correct measuring gear its hard to sya how much force is being put on the rope....

[dgcunningham]

60% is a pretty good rule of thumb. 55% was what the actual test was rated at without a margin for error and only 3 tests were performed, hardly conclusive. For the weights of the load, I worked with cranes on the railway for a few years and their training 'unofficially' suggested (as we were never supposed to lift a load without knowing the weight) 'have your best guess at the weight and then add a third, don't be tempted to fudge the figures to fit the system'. Seemed to work pretty well, only ever seen one crane nearly roll and those SLIs were screaming most of the shift!!!

[brachiator]

60% is a pretty good rule of thumb. 55% was what the actual test was rated at without a margin for error and only 3 tests were performed, hardly conclusive. For the weights of the load, I worked with cranes on the railway for a few years and their training 'unofficially' suggested (as we were never supposed to lift a load without knowing the weight) 'have your best guess at the weight and then add a third, don't be tempted to fudge the figures to fit the system'. Seemed to work pretty well, only ever seen one crane nearly roll and those SLIs were screaming most of the shift!!!

 

bits possibly third more than you think, you gotta love it and live by that rule, specially if you like your ropes to have a life lol.... (bit like slicing wood to fit your chipper without maxing it out (i.e stress and strain), seen some stress and then ive seen ropes take strain to the point of snapping, some stuffs just way heavier than you 'think', (communication with the rope man for anchor points on difficult trees is essential for me, i know from holding the rope on the ground, responsibility for climbers safety is on you! (i explain trees to folks in the same way, you can stress them but it'll recover as soon as you put strain on the tree it loses life) "if in doubt throw it out" Ross Smith, , alpine butterfly seems a pointless knot to me i use bowline with a bight for any midline knot (the marlin spike way) (not on the bight like they tried to teach at my school, that ones BS and cinches hard under heavy loads)

[Ian88]

I have seen and used it for industrial rope access and also for access into large tropical trees when you make a Y hang, i.e fig nine knot and alpine butterfly used to distribute one ropes load between two points. Its a nice easy one to adjust how big the loop is. Its also used for excluding damaged sections of rope and points of attachment in a line with minimal gear.

[DemonHedgeMaster]

I use it for force doublers but switch to a bowline on a bight for heavier rigging. using it on the end of tag lines to change the load angle on my wrists and a string of them at 1ft intervals makes a handy little rope ladder!