I am rethinking the safety of something I’ve been doing for YEARS. Specifically, knots – the use of them, the strength of them, the validity of them. There’s a handful of knots that we learn early on in our climbing days and once we learn them we don’t give much thought to how or why they work. As long as they are working we kind of forget about them. One such knot, a very simple knot, is the girth hitch. It’s used in many different ways – rigging top-rope anchors, linking slings to harnesses, anchoring a belayer to the ground…the list goes on. I always knew that knots were the weakest point in a system but it wasn’t clear HOW weak until I read this article on BD’s website.
The article compares the strength of three different knots used for linking runners together. The knots compared were the girth hitch, the strop bend (basically a girth hitch on each runner) and the climber’s hitch. They compared various knots using various diameters of nylon and dynex slings (spectra was not tested here). They found that joining two slings together using knots could reduce the strength by more than 50% – that’s over half the strength of the system! If you combined two different diameters of runners the system is even weaker – the thinner the sling material the greater the reduction in strength.
Of the three knots tested the strongest knot was the climber’s hitch. Oddly, I had never seen a climber’s hitch! I am making it my mission to learn it.
The best thing to do is use a locking carabiner to link slings together – if you have a choice don’t use a knot to connect slings. If you are going to connect slings, connect them using the same diameter webbing and use the climber’s hitch.
I needed someone to remind me so I am reminding you – check your webbing, runners, and quickdraws and get rid of them if they look worn. I’m going to go through my stuff and retire any of those old draws and webbing that I’ve been using for years.
If you are interested, there is a lot more good stuff on the QC with KP page of the BD website, including the most recent article which deals with retiring old ropes (I am guilty in this department too). Reading this stuff will really put into perspective some of that gear you have on your rack that you might not think twice about using.