Use of in-line figure of 8 knot

[Fulk]

Sometimes when tying a butterfly knot with a long loop I get a bit . . . well, tied up as it were, and I wonder if an in-line figure of 8 (see below) would be an acceptable alternative. Does anybody have an opinion / knowledge on this?

 

[Mark Wright]

I was first introduced to the In-Line Figure of 8 in the early days of the rope access industry in the late 80's.

The person who introduced me to it called it a Lazy 8. I remember seeing some breaking strengths for them many years ago but I can't remember exactly what they were. I do remember them not being much different to a conventional Fig 8, leading to some of the early IRATA training centres teaching them as an alternative to the Alpine Butterfly.

I've always preferred the Alpine Butterfly.

 

[ChrisB]

It only takes a load in one direction, pull the loop the other way and it will slip. To me that makes it inferior to the alpine butterfly and the figure 8 on a bight. I don't see any advantage over the 8 on a bight, unless it's stronger.

 

[Mark Wright]

It only takes a load in one direction, pull the loop the other way and it will slip. To me that makes it inferior to the alpine butterfly and the figure 8 on a bight. I don't see any advantage over the 8 on a bight, unless it's stronger.

If tied neatly (dressed and set) they definitely share the load well when used as a 'mid-rope' knot to create a 'Y' hang and don't deform. I don't remember them ever slipping on the few occasions i've used them, some of which were with rescue loads and when in a 'Y' hang configuration and being fully suspended below the rope loop. They were just as difficult to untie after a rescue load as a conventional Fig. 8 on the bight.

I'm pretty sure the testing was done as part of an IRATA Assessors workshop many years ago. They did both static and dynamic testing in both configurations, i.e., rope loop failure and main line failure. I'm pretty sure the knot immediately locked tight in the tests with minimal slippage, and was a fair bit stronger than a conventional Fig. 8 on the bight being loaded 'abnormally' in a rope loop failure. Unless the rope is chemically contaminated or rubs, or could rub over a sharp edge, I see no reason why the rope loop would fail. It's much more likely the anchor will fail and leave the rope loop intact, so any slippage wouldn't be safety critical. Any slippage would more likely be a benefit by offering an additional element of energy absorption.

I think we can sometimes get a bit too concerned about the rope breaking strengths for the different knots. However badly they are tied, none of them are ever likely to come anywhere close to failing with the forces we might potentially put on them. Even a badly tied Bowline in a typical 11mm Type A rope would be stronger than the minimum strength requirement for a PPE anchor that you might attach your rope to in an industrial environment.

I still prefer the Alpine Butterfly. It doesn't slip, you can load it in any direction and it's more than strong enough.

 

[mikem]

Is it really any easy to tie than a butterfly?

 

[andrewmcleod]

And almost certainly harder to untie afterwards...

 

[Fulk]

Thanks for all your replies.