Climb skills: Ropes & belay devices

Posted by Jonathan Garside on 05/03/2006
Skinny or fat - what's your preference?

Like many climbers I’m a jack-of-all-trades. I climb trad, sport, big walls, winter routes, boulders and plastic. I own half and single ropes ranging from 8mm to 10.5mm, and a selection of belay devices to suit. Currently a Reverso, Reversino and GriGri fight for space in the bag.

Equipment manufacturers strive to make their gear as light as possible, and it’s hard not to be impressed by the advances made over the last few years. But when it comes to belaying, light is not always right - you need to consider the rope and belay device as a team.

In the old days there wasn’t too much choice. The original belay device was the sticht plate, which used a grabbing action as well as friction. Then along came the Lowe Tuber and the Black Diamond ATC. These allowed the rope to be controlled more fluidly and proved immediately popular, setting the trend for todays devices. Yet at the same time, ropes have been getting thinner, and the wrong combination could catch an unwary belayer out.

Getting skinny
Take the Beal Joker rope, it’s 9.1 mm in diameter, and passes all three UIAA standards as a single, half or twin rope. Sounds perfect? Perhaps, but Beal make the following important point on their website, “Used as a ‘single’ this rope may not be grippable by all hands, and in all devices: in effect its fineness makes it a rope which demands expert holding and controlling. Classic devices, designed for higher diameter ropes, will give reduced braking, and some self-locking auto-brakes may simply not work.” In short, combining this rope with a poor choice of belay device and an inexperienced partner could mean you hitting the ground.

The right device
So how do you choose the right belay device? Well, there’s no UIAA standard for “grippability” as it’s proved very difficult to design a standard test, so personal judgement must be employed. As an example, my Reverso can be used with half ropes (8-9mm), but on my 8mm ropes I’d opt for a Reversino instead, being concerned about the braking ability of the bigger belay device. Another climber may disagree, but you just need to consider the facts and come to a decision yourself. Think about the rope’s diameter, the relative weights of climber and belayer, and how effectively you’ll be able to grip the rope. And if you have a variety of ropes, you may need to have more than one belay device

Impact force
Usually ignored by climbers, the impact force is the force transmitted to the climber and other elements of the system at the moment a fall is arrested. When a falling climber comes to a stop, the rope absorbs much of the energy created by the fall - the other main energy absorbing elements being the belayer, the climber, and most crucially, the top runner. Every rope has a stated maximum impact force (MIF), stated in kilo Newtons (kN), and this provides an indication of its energy absorption characteristics. Given two ropes of the same standard, one with a low MIF will absorb more energy than one with a high MIF, giving a lower force transmitted to other elements of the system. This comes at a price, as lower MIF ropes will be more stretchy, giving longer falls. For example, bungy cord has a very low MIF, but you’d fall a veeeeeery long way, whilst static line has a very high MIF, but a leader fall could be catastrophic.

During a fall, the top runner sustains the impact force generated by both the falling climber and the force held by the belayer. In total, the force exerted on the top runner is about 1.6 times the force exerted on the climber - the pulley effect. It’s not surprising those top runners fail! It’s long been known that grabbing belay devices result in a greater force on the top runner when compared to more dynamic belay devices, and tests carried out by the Italian Alpine Club demonstrated that ropes with a lower MIF can also result in a lower impact force on the top runner. In one test using a conventional belay device, there was a 30% increase in the load on the top runner when a rope with a 10kN MIF was used, compared to a rope with a 7kN MIF. This increased to 35% when a grabbing belay device was used - the science behind the reason that you should leave the GriGri (a grabbing device) at home when tradding at Stanage or hitting some ice.

Conclusions
When choosing a rope look at its MIF. If you do a lot of ice or trad routes, using ropes with a low MIF and using a non-grabbing belay device is a good idea. But when sport climbing, a rope’s MIF may not be such an important consideration as the bolts should not fail. Using extenders effectively to ensure the rope runs as straight as possible will also greatly reduce the impact force on the top runner.
 

EXPERT Q&A

This issue the climbing expert is Andy Perkins. Andy is an IFMGA Mountain Guide, based in Chamonix. And in a past life he used to work for Troll Equipment as an equipment designer and rope access and rescue instructor so should know, er, the ropes. See www.climbex.u-net.com.

Q. What’s the difference between single and half ropes?
A. Single ropes are stronger, less stretchy, thicker and heavier than half ropes.  If you’re using just one rope to climb (e.g. sport climbing, indoors) then choose a single.  If you need two ropes to reduce drag (e.g. trad) or to do full length abseils, then go for two halves.

Q. What length of rope should I get?
A. Anything less than 50m is a bit passé these days, so go for 50m for British trad and alpine, 60m for UK sport climbing and continental icefalls and 70m for the odd continental eurosport venue and certain Mal Duff routes on Ben Nevis!
 
Q. Is it safe to buy second hand ropes?
A.
Absolutely not.  You have no idea of its history; how it’s been stored, how much use it’s had, and crucially whether it’s had to take any big falls.  All of these things can drastically affect the rope’s ability to absorb the energy of the fall and to withstand the maximum impact force.

Q. When should I think about retiring a rope?
A.
Manufacturers are obliged by EU regulations to give what’s referred to as an obsolescence period for ropes.  Different manufacturers will look at this in different ways, but as a climber you should check the instructions that come with a rope first, and then keep a constant eye on the state of your ropes.  If they look worn or thin, then think about retirement.  If they look or feel damaged, then do retire them - now.

Q. What’s the best belay device for a beginner to use?
A. I’m with Jon Garside on this one: Assuming a beginner is going to be using single ropes, the Reverso is a great choice, with no moving parts, and clear diagrams on the side to indicate how to thread it up. Whichever brand you end up with it should be simple and moderate to grabby.

Q. I’ve heard GriGris are dangerous. Is this true?
A.
There is a misconception that because the GriGri is an autolock device it’s suitable for beginners. This has resulted in some nasty accidents, either through a misplaced sense of security or an inability to balance the position of the lever against the tension on the dead rope.  I think the GriGri is a great device, but needs more training and familiarisation than a device with no moving parts, and an awareness that you still always need to keep a hand on the dead rope. 



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