UKC

Hi guys,
I'm considering getting some Dragons, but have heard that the sling is not particularly durable, and needs to be replaced within 2-5 years, depending. Now, I am 100% aware that DMM will resling them for cheap, BUT it is quite likely I will be nowhere near Wales in 2-5 years time, and I don't enjoy the thought of posting a box of metal across the world to put a sling back on. Secondly it also feels a bit like posting your lamp to change the bulb.

So first off, wondering if anyone has any experience doing it? (I know Andy K is happy to tie Dyneema: http://www.andy-kirkpatrick.com/articles/view/equalising_slings_and_cords)

Secondly, I have done some research as to how to replace the sling (without sacrificing strength):

- Dragons are rated for 14kN: http://dmmclimbing.com/products/dragon-cams/

- Dyneema is slippery as heck, and most traditional knots will slip in it rather easily.

- A sewn 8mm dyneema sling will fail at about 26kN, while one tied with a Triple fisherman's will fail at 17.6kN (according to DMM themselves: http://dmmclimbing.com/knowledge/knotting-dyneema-vid/ )

- There are many new knots that are stronger than triple fishermans, EStar hitch and this one: http://l-36.com/bend_knot.php and some in here: http://igkt.net/sm/index.php?topic=4756.0

- These new knots are somewhere from 1.3X - 1.5x stronger than a triple fisherman's (according to the sites listed above) - which roughly puts an 8mm sling tied with one at a breaking force of 22kN or higher. This is also quite a lot higher than the rating of a dragon already, and is approaching the strength of a sewn sling. The testing is quite thin however, so much more data points are needed.

So, it seems it is feasible. Now I'm not a maniac, and would need to test this fully first before considering. But maybe this is interesting for others anyway, maybe you didn't yet hear of the new knots that are stronger than triple fishermans.

As a side note, here is some research done on cowstails by some French people: http://www.bethandevans.com/pdf/lanyard_tests_v6.pdf
Basically they found that sewn slings are absolute crap at absorbing forces (which is not only dangerous for you, but for the slings) , and instead the best cowstails for absorbing force are made from loops of rope tied together.

In reply to SenzuBean:

I'm not sure why you'd even consider it when you can send them back to DMM to replace properly.

Package them properly and they're not going to get damaged in the post.

Slings are static, so yes you need to use them appropriately. There's nothing wrong with using them as a cows tail as long as you are sensible and aware of their limitations.

In reply to jezb1:


Indeed, but if there's a better tool for the job, then it's probably worth considering

In reply to jezb1:



Some people like to be able to fix things themselves Especially if it's possible, which is what I'm suggesting.

In reply to SenzuBean:

Hi, looking at the sites you listed I think they are pulling a different material than used in climbing slings. Hopefully someone in the know will pop along soon, as I'd like to know what's best too but for different reasons

In reply to SenzuBean:

I have considered but don't really consider other options better for general climbing scenarios or my work.

Re. The cams, of course you can do it yourself but it won't be as neat as the original sewn sling. Personal choice of course.

In reply to SenzuBean:

Big no no from DMM

dmmclimbing.com/knowledge/knotting-dyneema-vid/

In reply to David Coley:


They are dyneema (HDPE) pretty much. Climbing slings are a blend of dyneema and nylon (the ratio is proprietary AFAIK), but since they're called dyneema and the melting point is so similar to raw dyneema, it's likely to be almost all dyneema. They are using round core, as opposed to tape, but the slippage problem of dyneema is the same (it's theorized to be related to the low melting point - it melts at the skin layer which lubricates enough so that everything can slip through).

In reply to Rick Graham:



Indeed - I linked that in my original post
But if you read what I posted, you might see why I think it might now be possible to tie a dyneema sling when considering these new knots, which could theoretically bring the tied sling's strength into line with a sewn one.

In reply to SenzuBean:

>

I´d be reluctant to transfer the relative strengths of knots from one material to another, the stuff they are testing (Amsteel) is nothing like the materials we use and the failure modes are generally different. I´ve pull tested some of it and believe me it´s pretty wierd.

In reply to jimtitt:

Have you access to a pull tester? Maybe you can test these new knots to see how they work out

In reply to SenzuBean:

Whenever the Dyneema slips (as it must do with any knot) it would appear to reduce the breaking strain considerably particularly in dynamic situations. Some of this could, theoretically, be reduced by keeping your knots tight but given the tendency of Dyneema to work itself loose over time this would need constant checking.
There are people who recommend that you don't even Knot a sewn Dyneema sling.
I'm quite glad you started this thread as it has convinced me that securing Dyneema by Knotting is to be avoided if at all possible.

In reply to SenzuBean:

Why bother, knotted slings on cams make for an awful bulky mess. Unless you get unlucky or you're frequently careless with them the standard slings will last for ages. When they're getting tired, bite the bullet, take an opportunity to get them re-slung when it crops up. Your other option of course is to just push a pre-stitched sling through and clip both loops, that's how I re-sling my cams.

jk

In reply to DubyaJamesDubya:



Actually that's why I'm excited by these new knots - they don't slip! They break, and at approximately 40-50% of line strength (this means it would be 50% as strong as if you had an sling that had absolutely no joins, no sewing, but was one continuous loop). Triple fishermans were slipping at around 25-30% line strength. A sewn joint also reduces the strength to somewhere between 50-60% of line strength, so these knots are coming very close to sewn strength. This is cutting edge knot research :p

And yes - knotting a sewn dyneema sling will drastically reduce its strength. However, there is a tradeoff - if you knot it and thus have a much shorter distance to fall, you won't apply as much of force onto it as well. Whereas if it's long and unknotted, it will be stronger, but you will be putting a much bigger force onto it.

In reply to jkarran:

... Your other option of course is to just push a pre-stitched sling through and clip both loops, that's how I re-sling my cams.


I've done that in the past.

In reply to DubyaJamesDubya:



Then you can't do the cool extending options that the stock slings can do, if I'm not mistaken. With stock you can clip both legs, or pull one down all the way to the stem and clip the one, now twice as long leg. Plus can tie knots to have any length between extra long and short - all for "free".

In reply to everyone:

I'm taking it that Larks Footing a new sling onto the cam is a No No?

In reply to Lusk:
Would using cord with a double fisherman's work? Plenty of people have cord on their hexes.

Neil

In reply to Lusk:


Your call but I sometimes extend mine like that. Data that came with my 6mm slings says 16kN larksfooted (onto what?) and anyway, what forms at the cam stem if you do it right isn't a true larksfoot anyway, it's basically just a slung pin (the cam stem) then the sling running over a couple of blunt edges (the sling hole). Downside is it imposes a small bending load on the cam stem.

jk

In reply to Neil Williams:


It's what I've been thinking since the beginning of the thread, I think that's the way I'd do it!


JK, I was thinking of cams with the loops.

In reply to SenzuBean:


I'm not sure that makes sense. If knotting a sling of any reasonable length on a cam can make the fall "much" shorter the fall must be very short indeed, of the order of a foot, or you fell off the belay ledge. It is therefore unlikely the strength of any sling would matter.

In reply to David Coley:


Sorry I got carried away and was talking about cowstails at anchors specifically with regarding the strength of a sling. I.e. at a belay stance, you can either fall a shorter distance onto a weaker sling (probably the better idea, as energy goes up by a square ratio to distance fallen - fall twice the distance, 4x the energy has to dissapate, while the knot will only weaken the sling by a max of about half), or a longer distance onto a stronger one.

In reply to SenzuBean:


Methinks you should do a bit more research!
Original Dyneema hybrid tape has a rated strength of around 16kN and sewn slings hold over 22kN and break at the pins, not the stitched joint, the sewn part is not the weak point.
Tape and cord strength is measured differently than finished (sewn) slings.

In reply to SenzuBean:


Why would you fall any distance on to a sling at a belay stance? You were the one who posted the link to yet another report pointing out for the umpteenth time the fundamental point that every climber should bloody well know: that it's a really bad idea to rely on a static system for fall protection.

In reply to jimtitt:



Care to provide this research?

And yes - I would love to actually do some tests on tied slings with these new knots and see how they perform. I'm not suggesting anyone do anything rash - just to consider that a tied dyneema sling might be a possibility with a type of knot that is a lot stronger than triple fisherman's (which even from DMM's own research, was still surprisingly strong - stronger than the cam was rated for).

In reply to Martin W:


I did not recommend falling onto the sling at all!
It is however a widely recommended practice to clip to an anchor with a cowstail - It's also recommended for people setting up single pitch top/bottom ropes as well while they're working above the cliff (p114 Mountain Skills Handbook (2009 Pete Hill, Stuart Jonhston) - "
*Personal Safety When Rigging*
Your own safety is extremely important - you are of no use to the group if you are lying on the bottom of the crag in a strange shape. When rigging, running an activity and de-rigging, always look after yourself and don't take risks.

Methods:
- The simplest is an 8ft (120cm) sling lark's footed onto your abseil loop as a cowstail. Have a screwgate karabiner on it, and it will be ready to use by clipping into an existing anchor or rigging loop. This method is extremely useful if you are moving between a variety of sites. When not being used, the sling can wrap around your waist and the krab can be clipped in to stop it flapping about."

So clearly it's not a sentiment yet shared by everyone that falling onto a sling is a wildly dangerous thing to do.

In reply to SenzuBean:

'Back in the day' everyone just made runners out of knotted nylon tape. I have re-slung cams with nylon tape and knotted it with a tape/water knot before with no problems at all.
I always think a mix of nylon and Spectra/Dyneema slings is best as you can use the appropriate material when necessary.

http://www.rockandice.com/lates-news/spectra-versus-nylon?page=1

In reply to Lusk:


Cams with swaged wire loops? Bearing in mind the problems BD had getting the Camalot wire loop to survive with a thin dyneema sling attached I think it's something I'd avoid. Cams with big loops don't need slings, cut off the tat, rack them on krabs and clip with an extender if you can't get them properly reslung.

jk

In reply to JamieAyres:




Lots of interesting advice:
2. Fall onto the first piece of pro: As in a daisy-chain fall, when you drop onto the first piece of gear—a common scenario on multi-pitch routes—you hit hard because there’s little rope in the system to elongate, and decelerate your fall. To soften the blow, use a nylon runner on your first piece. Though nylon stretches ever so slightly, at least it stretches some. (Also, use a fresh rope with a low impact-force rating, which will keep forces even lower.) As you climb past that first piece and introduce more rope into the system, thereby lowering the fall factor, you can runner-up the rest of the pitch with light and tidy Spectra.

3. Fall onto a sling girth-hitched to your harness: Another common mistake, this happens when you girth-hitch a sling to your belay loop and clip the sling to a placement to hang and rest, or to temporarily anchor yourself independent of the rope. Then, you either slip and fall onto the sling, or resume climbing, forgetting to unclip ... and lob. Again, the fall factor—and forces—are extremely high. Use a nylon sling instead of a Spectra one as your impromptu “daisy.”
<-- According to my last link from the OP, even better is a hand-tied sling (of material with dynamic properties) to use as your cowstail.

Thanks for the link Jamie. I'm fairly certain you're not the only one who has reslung their own cams and been quite alright. It would be nice to get some more testing done - I think that's the next step

In reply to SenzuBean:


It is. A wildly dangerous thing to do, I mean. There's nothing wrong with using a sling to stop yourself from being able to topple over an edge, though - it's all about the length.

I think the reason you're getting quite a negative reaction is that this method hasn't been tested in the situation you're proposing to use it. What you actually want to do are pull tests with real dyneema slings in the configuration you describe - and a knot can be stressed in at least two orientations depending on the positioning of the sling. Climbers are quite averse to changing critical things like knots without proper testing; this might be darwinian, the ones who aren't averse to doing this sort of thing are dead.

Also, the way we do things isn't always the best. Rethreaded figure of 8? Quite a s**t knot. Flat overhand, even more so. However, it is way more than sufficient for what we use it for, and other factors can be important - doesn't work loose, easy to tie, visually obvious if it's correct, and so on. Personally, I wouldn't want to use some of the knots you've shown because they're complex, and if you get a knot wrong you can be dead; I wouldn't be confident I'd tied it correctly. Confidence matters, too - when you're above that cam, you don't want the gremlins to start.

None of the above is actually a reason why not to do what you propose, but you may want to give it some more thought.

P.S. Did we climb as a group last July - your first climb? LMC?

In reply to climbwhenready:






Hey mate - yes that's me, I recognize you too Managed to catch the climbing bug hard that day!

I think what has happened is that using a _nylon_ cowsling to tie in was fine and quite safe for many years, and when dyneema came along - that method of securing remained without everyone realizing that dyneema is not suitable for doing that.

Important point to remember is that I'm not proposing a new knot to be tied "in the field", but rather from the comfort of home, with hours to tie and quadruple check it. Those knots can in my opinion be a lot more complex than something you need to tie in the dark when you're trying to avoid an epic. You'd never resling a cam in the field with these knots.

Anyway - will have a think about how to get some testing of these knots done.

In reply to SenzuBean:


doesn't E=mgh imply that if you double the distance fallen, you double the energy?

In reply to David Coley:

Yes you're quite right. Here's a handy calculator that shows it quite clearly: http://hyperphysics.phy-astr.gsu.edu/hbase/flobj.html
I had E = 1/2mv^2 in hand and wrongly assumed velocity doubled.

In reply to SenzuBean:



It´s not research it´s common knowledge, at least in my bit of the climbing industry.
The problem with the "strong" knots described generally is they overcome the problem of slip by adding anynumber of turns before the pinch part of the knot. This means in a dynamic test the performance will almost certainly get worse and worse since there is more material to slip inside the knot. Slow testing is easy enough but drop testing a whole new level of difficulty and expense.
Personally I would just either get my cams re-slung since it´s cheap and readily available on most continents or if the cams are too old then I double a thin sling through and don´t expect the world. If it had to be a knotted solution (and this isn´t my preffered solution) then I´d go for Ultratape or better Edelrid Tech Web since it´s a)stronger than normal dyneema tape and b) designed to be knotted or Tech cord.

In reply to jkarran:



Aye, that makes sense.

I think our OP is completely overthinking a (non existant) problem here!

In reply to SenzuBean:


you were not wrong. The velocity will double, via E=1/2 mv2. Both E=mgh and E=1/2 mv2 apply.