UKC

see title.....someone on another thread mentioned they could, I've never done it, and I think was told by a Plas-y-Brenin instructor not to.

In reply to collism:

Not really, no. At a very narrow angle at the wide end you could get away with two slings or whatever, but not a proper three way pull.
They were originally designed for Italian hitches I believe.

I thought so, just wanted to check

In reply to collism: No, no crabs can, if it is going to be loaded 3 ways use a maillon.

In reply to peterjb: How do you go about building a belay with spread out placements without 3 way loading?

In reply to Alasdair Fulton:

One way is to bring the two slings together, tie a big overhand knot in the two together, so you've got a double loop at the end, and clip the krab into that.

Good question, anyone.....

In reply to Alasdair Fulton:

bring your anchors to one point using an sling/rope using an overhand knot and clip that one point to a screwgate.

Overhand knots are not much use when your setting up a hanging belay, clinging to a sheer face,

I was instructed by Plas-y-brenin guy to feed the rope through 1st anchor attaching the return rope onto a Krab with a clove hitch , then continue with 2nd and 3rd anchor

Technicall you have loaded the Krab 4 times (3 anchors and harness) though the rope to anchors is taut so if partner falls there's little movement, therefore the load isn't a problem

In reply to collism: What's the maximum angle you can load the wide part of a crap at before it's considered 3 way?

Does 10 degrees make any difference?

In reply to Alasdair Fulton:
I think the general rule is that two anchors less than 60 degrees apart is preferable, and more than 120 degrees is a bad idea.

Thats fine for anchor advise setting up, but even if you have 3 anchors within 60 degrees you still have 4 loads on the Krab

What are the mechanics behind 3 way loading failure?

Does the crab fail due to the increased load or is the gate that fails?

Is it because the crab is designed to take laod down it's spine and not across the wide radius at the top?

I wish I knew - someone with a physics degree - please answer

In reply to collism:
There is an even easier answer to all this, and that is to buy two small krabs for a fiver each, rather than buy one large one for a tenner, and then you won't need to attach both anchors to one krab.

The rule about anchors not being more than 120 degrees apart still applies though.

In reply to collism:

The continentals seem to think that 2 or 3 slings, ropes or whatever clipped into the same krab is ok. Must admit that I do this when on bolted belays.

http://www.planetmountain.com/english/Lab/techniques/bolt-belays/2.html

JH

I have 12 Krabs and after a pitch and setting up belay, I generally don't have 3 Krabs spare not to mention the mess of 3 Krabs with clove hitches a Krab to belay and a figure of 8 knot

In reply to collism:

3 way loading doesn't mean having more than 3 loads on one krab. It's the direction of loading rather than number of loads that's the important factor in failure.

In reply to collism:

Get a long sling for setting up belays. It saves all the faffing with the rope, makes the belay more versitile, prevents any problems with 3 way loading, and means that you have all the rope for the next pitch.

Mark

So it basically boils down to the angle then, not the number of loads?

eliminate the angle from the question, it doesn't matter

lets say they all around 60 degrees

I agree with the sling method, if your safe, but how do you tie a overhand knot and equilise the sling with one hand

In reply to collism:

three separate krabs is a lot tidier than faffing around with three clove-hitches on one krab IMO...however, I don't practice what I preach because I also frequently run out of screwgates and have to double up on anchors.

The worse case scenario is running out of krabs alltogether and having figure8 the anchors to the loop - now that is messy!

In reply to collism:



If your that desperate, ie your halfway up an E5 multipitch with hanging belays midway through a 6a move, you could always just clip into one of your anchors with a sling or a quickdraw, sit on it, then arrange the rest.

3 way loading is something to bear in mind,
but any stretch will decrease the angle and especially with a belay where it won't take the load of a lead fall (a lead fall uses your weight to assist in holding it, and when building your (e.g. hanging) belay you weren't worrying about absorbing a large upward pull more than you were worried about anchoring your ass to the cliff), and with friction over the edge of a cliff, you're going to struggle to generate enough load to break a krab.

In reply to Paz:

Thanks the best answer I've seen

In reply to collism:

I beg to differ.

Assume you have 2 anchors at 120 degrees apart. You then apply a third load, such as a falling climber, again at 120 degrees. Therefore the krab is being loaded in 3 directions. Krabs aren't designed to load like this.

Assume you have a krab attached to 3 or 4 anchors, but the anchors are all within a few degrees of each other. Now when the krab is loaded the stress on the krab is reduced as the loads from the anchors almost act in one direction.

You assume wrong, lets say all anchors (lets say 3) are all within 90 degrees

The krab is attached to harness and 3 clove hitchs to each anchor

Technically you have 4 loads on the krab

In reply to collism:

The difference between an HMS and a normal D screwgate is that, because the load is through the centre of the krab (the bottom of the wide curve), both of the straight 'arms' have to share the load (as opposed to the D where the load is primarily through the spine and the gate side is weaker). For this reason, 3 way loading of an HMS is not the "no no" some people think it is.

Krab happens not due to in plane loading but because of either gate open (hence a screwgate) or twisting or bending forces (a twisted fig 8 descender, or the krab over a rock edge).

In reply to GrahamD:

That's "Krab breakage happens", obviously.

In reply to GrahamD:

Your explanation is not quite right. Interesting piece in the AMI journal last month about this. HMS shouldn't be any more loaded than any other type of krab. The strength is in the back bar in all but ovals and maillons.

In reply to collism:

If you want a proper mathematical answer to this, either a, buy an A-level maths/physics book or
b, buy a decent ropework book which will explain all your questions quite easily.

I would tell about you angles properly but I really can't be arsed so in brief if you have 2 anchors on a belay which are 90 degrees apart and your second falls of creating a 1KN force (easy number to work with), 1KN goes to each anchor, if the angle was 45 degrees 0.7KN would go to each anchor, and if you were stupid enough to put them 120 degrees apart 1.73KN would go to each anchor, a total force of 3.46KN even tho your second only generates 1KN! Hence a good reason to keep your anchors close together! As far as three way loading goes its a bit more complex but krabs are designed to take loads in line with the back bar (bit opposite the gate), three way loading doesn't do this.

Hope this was of some help, it's much easier to see it all drawn out.

In reply to beermonkey:

Your 90 degree figure is out. It's in the 70-75% figure.

In reply to collism: Complete load of nonsense.

Of course krabs can take at 3 way loadings!

However their strength will not be as much as the '3 sigma' guaranteed strength of 20+kN they have when loaded 2 ways along the major axis.

Based on a quick consideration I would suggested that I can't see how a 3-way load should be any worse than a krab in it's weakest configuartion i.e. cross loaded. Therefore it should be possible to use the krabs minor axis strength rating (e.g. 6 to 9 kN) as the basis for the MINIMUM stength in a general 3-way load scenario.

In most 3-way load scenarios 2 belay anchors are being equalised and attempt is made to orientate the karb in the best possible manner. It is in this regard that HMS krabs are particularly good. Assuming that the largest internal load on the krab is aligned along the major axis, the minor axis loads can be calculated for differing angles between the resulting loads.

For normal angles between anchors this is striaght forward and these estimate can be made:

60 degress
Max load <= 3.46 x Minor axis strength
90 degrees
Max load = 2 x Minor axis strength
120 degrees
Max load = 1.15 x Minor axis strength

However at very wide angles greater than 127 degrees it will be actaully be safer (and more natural) for the karabiner to be orientated the 'other' way from normal with the minor axis taking the resultant belay load. The anchor loads 'pulling it apart' are likely to force the krab into that orientation anyway.

Therefore for around 127 - 160 degrees
Max load = Minor Axis Strength

With most karabiners the minor axis strength is 6-9 kN. Therefore it is easy to see that two anchors/loads with no more than 90 degrees between them are of little casue for concern. However load angles approaching or exceeding 120 degrees cause a mcuh more worrying reduction in strength.

This tallies exactly with what is normally taught when considering belay anchors -
60 degree OK. 60-90 degrees poor. 90+ degrees avoid!

However, even in the worst case the strength should be at least that of the minor axis strength rating of the krab.

Hope that helps.

In reply to brt:

I thought it was sin90 that configuration, hence 1?

In reply to beermonkey: cos45 is it not?

In reply to Mark Stevenson:


That is very much more to do with the load on the anchors rather than on a hypothetical single krab in to which two or more independent anchors might have been clipped. It's a bad idea to build any belay with obtuse angles between the tie-ins to the anchors, whether or not they all bear on one krab.

In reply to collism:

In practise I can see no reason to actually have to use a crab in this way, even if you've run out of other crabs. So I guess some very hypothetical calculation of strength should be needed.
Personally I'd rather not be sat on a belay working out the relative strength of the one crab i'm clipped to, when i could use a sling or pull through more rope to avoid the situation.

Wil

In reply to katonka:

Should NOT be needed.

In reply to katonka:

Yeah, I avoid this problem entirely by tying the rope from the anchors into the tie-in loop of rope on my harness with a figure of eight.

In reply to Martin W:

That was precisely the point I was making. The guidelines are based on anchor strength, not karabiner strength but the same rules/conlusions apply directly to the case of using a single karabiiner.

In reply to collism:

Doesn't need a physics degree, its either A-level matths/physics or postgrad metallurgy. Crabs will take a large force along or close too the main axis. i.e. parrallel to the gate. They will take less force (usually around 1/3) perpendicular to the gate due to the gap in one side. With two forces pulling in opposite directions it is asumed the krab is able to re-orintate so that the forces align along the major axis. IF a 3rd force is added along the minor axis the krab can't reorintate and you get a significant cross loading which can cause failure. With 2 or more anchors being added to a single krab the forces should be pulling in the same direction and therefore be safe. If the anchors are more than 60 degrees apart then you get a significant force generated in the anchors perpendicular to the major axis (in order to produce the reaction force along the major axis). This will make the system unsafe.

The main problem with this is that most krabs can't accomidate 2 knots or slings at each end. For an HMS the wider end can take 2 clove hitchs so you could use it to join two anchors SO LONG AS THE ABOVE CONDITIONS ARE MET. However you would not then be able to use it for your belay device as you would no longer have room to use it.

Also if anchors are more than 60 degrees apart each individual anchor will experiance more than the load applied to the system. That is the system will be LESS safe than a single anchor.

BTW loads in this context are the climbing rope and the anchor atachments. body wieght (unless you are outragously obease and insist on carrying the kitchen sink in your rucksack) is about 1/10 of the cross-loading failure point.

belay device, ground anchor and climber cliped to one HMS should NEVER give a 3 way load cos the belayer should still have their feet on the floor!

In reply to brt:

An HMS doesn't have a back bar - its symetrical so the load HAS to go through the centre of the krab and so it will be equally shared between the two bars - or did you mean something else ?

In reply to davidwright:

Sorry if the anchors are 60 degrees to the resultant force then each anchor takes more force than it would if used alone (cos 60 =0.5). but beyond 60 degrees seperation (i.e. 30 degrees to the resultant) you stop getting significant safty benifits from 2 anchors.

krabs always fail at the gate. even if load along the major axis. failure due to 3 way load occurs early because the gate is weaker when pulled open rather than streched.

In reply to all:

the discussion is interesting but at the end of the day it is all rather academic - how many modern carabiners have you heard of failing on a belay?

So keep your anchors within sensible angles, and bob's your uncle.

In reply to collism:

Jesus Christ. I just hope everyone (with a few exceptions) on this thread doesn't share UKC's distaste for the SPA. I suggest you go on a training course.

Don't three way load krabs. I think there used to be some nice examples of what happens if you do on the wall in The Castle.

I have one krab that is designed for two clove hitches but I normally use two or more krabs. It's not messy and it's easy to see if you did it wrong.

You have a hanging belay, makes no difference. Of course, if you were doing routes that required you to cling on by your fingertips whilst setting up a hanging belay then I'd imagine you'd have learnt how to do it confidently first.

In reply to all: I think the bottom line is that if you set up a good belay and belay properly, it doesn't matter. Even if you do have some wide angles in your system, the force of the second falling on the rope is unlikely to come even close to the breaking strains required to do damage. Add into the equation the friction of the rope on the rock and the belayers own body weight and I challenge all the number crunchers out there to come up with a realistic situation where the HMS krab may fail. Assume that the belayer at the top is doing his job properly i.e. not leaving 6 miles of slack in the system.

In reply to davidwright:


There's a photo on Needlesports' web site that says otherwise! Look at the section about the DMM Eclipse krab here: http://www.needlesports.com/acatalog/Mail_Order_Karabiners_22.html This krab was cross-loaded across the gate and, although the gate deformed (so I suppose argubaly it did "fail" at that point), the krab actually held the load up to the point where its back broke.

In reply to Jon Dittman:

Agreed. Deserves to be the bottom line again:

The bottom line is that if you set up a good belay and belay properly, it doesn't matter.

In reply to Martin W: So what? The krab failed at 13.5kN when it should have failed at 7kN. I would love you to show me a situation in climbing where you can load a +7kN cross load on a krab without doing something really stupid.

In reply to GrahamD:

Pedants corner

They nearly all nowadays have a slight downward curve so as to orientate the rope/sling towards the non gated side of the 'biner. That's where the strength is. Having found the journal I was looking for, the nearer the gated side a load is applied, the weaker (I use the word losely) the 'biner becomes (I think the figure was 14kn on a 24kn tested 'biner).

Oval 'biners load centrally which is reflected in there lower rated standard; 18kn IIRC.

It's all a splitting hairs'ish though. I personally feel that it's just as easy to do something right as it is to do it wrong... use a belay/rope loop to belay from; don't overload krabs etc etc. Why compromise?

In reply to Alasdair Fulton:


I wouldn't want to load a crap at any angle. I try to avoid treading in them!

In reply to Jon Dittman: "So what?" to you too. I was merely pointing out that davidwright's assertion that krabs always fail at the gate was demonstrably inaccurate.

In reply to Martin W:

Ok I'll accept that. I was thinking about the older style where I would expect the falure to be either the gate pin braking or the fastening hook going in a stiffer gate. For a properly loaded krab usual mode of failure is for the thing to straighten under load starting at the gate.

David

In reply to Jon Dittman:

At the belay with a modern rope you shouldn't get that kind of force even if you did do somthing realy stupid. peak loading in the rope is 8-9 kN. At the top runner you could get twice this if you took a long fall on to a high belay cliped as a runner but to cross load or 3 way load a krab there you would have to have done something really odd

In reply to brt:

I'll agree that there is not really any reason not to do things the 'right way' (meaning best practice - there is no one right way) and you don't actually need any krabs on your harness to tie in..

All I was pointing out is that HMS Krabs are not as fragile as some people seem to be making out and don't routinely fail, at the gate or anywhere else.

where those 3 way loaded by ropes/slings or leavered open by 8's?

in a trivial case an ATC cliped to a Krab cliped to a belay loop could be 3 way "loaded" but the 3rd load would be tiny.

less trivialy a clove hitch coming from one anchor and out to a second is also a 3 way "load" as the force on the krab would be on two diffrent ropes pulling in diffrent directions given the way the knot grips the krab. Is this really diffrent from 2 slings doing the same thing and overlaping on the krab? (BTW that set up anchor-clove hitch-anchor comes straight out of the spa handbook).

In reply to Martin W: Soz fella. I think I was a bit OTT.

In reply to GrahamD:


That we will agree on.

In reply to Jon Dittman: No worries, we each got our respective points made.

Why not just use an Alpine Butterfly, if you're worried about loading directions?

In reply to collism:
Not really. But in extremis, I'd rather 3-way-load an HMS than a snap gate!