Sling with larks-foot (girth hitch) a no-no?
Steve Pardoe
'Scuse a sort-of-on-topic article for once ;-)
I've been reading a 'merkin book about making the transition from gym [sic]
to crag, and it was suggesting tying a larks-foot (which they call a girth
hitch) in a sling to tie it round a tree, etc, such as when setting up
belays.
I seem to remember reading (or hearing) somewhere that this is a Bad Idea,
as when such a knot is shock-loaded, the nylon (or whatever) can melt, or at
least weaken, as the knot slips and tightens on itself (I've tended to use
a krab to link the two ends of the sling, instead, though of course this
effectively halves the length of the loop). However, no-one seems to worry
too much about knots in ropes.
Can't see anything about this on Stefan's FGA page at
http://www.cs.bris.ac.uk/~stefan/FGA.html . Is my concern just total
b*ll*cks (TM), or is there some truth in it?
TIA,
Steve
Tony Buckley
aspic, one presumes),
> Is my concern just total
> b*ll*cks (TM), or is there some truth in it?
If you read the little 'don't sue us if you die because this sling fails'
note that comes with them, it shows something about the relative loading
that different configurations can bear. AFAICR, a lark's foot arrangement
halves the loading the sling can bear. Whether this is due to melting or
not I don't know, but it's good practice to avoid using them.
Tony
Carol Haynes
single strand with a double strand. In a shock load the double strand will
cut the single.
I was told that the knot can reduce the strength to 30% of the slings
capacity.
Better to put the sling double round the tree and put a crab through both
end loops.
Carol
"Tony Buckley" <a.g.b...@dl.ac.uk> wrote in message
news:9du84t$pjm$1...@mserv2.dl.ac.uk...
Tom Hawkins
at Plas Y Brenin or something...
Tom
Carol Haynes <lairdswo...@SPAM.yahoo.ME.co.uk> wrote in message
news:9du9n2$6g5$1...@taliesin.netcom.net.uk...
Carol Haynes
Knots reduce the strength of anything when they are tied but not by a huge
amount for rope. I'd be surprised if there is a huge difference in slings.
Given that I do use tied slings at times I would appreciate any further
evidence people have of this. What about sewn slings?
Carol
"Tom Hawkins" <vertical...@bigfoot.com> wrote in message
news:tyCM6.21913$tU6.2...@news2-win.server.ntlworld.com...
Gavin Cox
> I find that hard to believe - does anyone have a reference anywhere?
Not quite larks footing around trees, but larks footing slings together to
extend them.
http://www.putzl.com/~klew/knot.shtml
Regards,
Gavin
Martin Whittaker
<lairdswo...@SPAM.yahoo.ME.co.uk> writes:
>I find that hard to believe - does anyone have a reference anywhere?
From "The Climber's Handbook" by Garth Hattingh: "A sling can be draped around
a tree or through a wormhole*. However, avoid using Lark's foot configurations
where possible, as these can weaken the sling by up to 75%!"
Now, whether you regard that reference as trustworthy is another matter, but it
is a reference.
>Knots reduce the strength of anything when they are tied but not by a huge
>amount for rope. I'd be surprised if there is a huge difference in slings.
From "The Handbook of Climbing", by Allen Fyffe and Iain Peter:
Knot strengths (percentages)
Unknotted rope 100
Figure-of-eight 75-80
Bowline 70-75
Double Fisherman's 65-70
Fisherman's 60-65
Clove hitch 60-65
Overhand 60-65
The same percentages are given in "Climbing: The Complete Reference" by Greg
Child.
Fyffe & Peter also state: "The lark's foot is a very simple but weak knot which
is generally best avoided, although it can be tied quickly and so has some
uses."
I wonder whether the advice against using a lark's foot in a sling is more
relevant with dyneema slings, which are narrower and thus will exert a greater
pressure on the crossing point when subjected to the same shock load? That
would also make the lark's foot bad for rope (which is what Fyffe and Peter
say), but perhaps less of a problem for 25mm wide nylon slings.
I'm interested in this question because I have a copy of "Climbing Anchors" by
John Long which specifically recommends using a girth hitch to secure some
thread or spike anchors. While the book is generally a useful reference on
setting anchors and belays, when I mentioned it to another climber friend they
said "Oh, I wouldn't trust anything in that book because it says it's all right
to use a lark's foot on a sling and everyone knows that's dangerous."
Anyone else got any specific references?
Martin
* This is the only reference I've seen to the use of anomalies in the
space-time continuum as protection placements!
Jeffrey Mazo
Martin Whittaker wrote in message
<20010517055720...@nso-md.aol.com>...
>
>From "The Handbook of Climbing", by Allen Fyffe and Iain Peter:
>
>Knot strengths (percentages)
>Unknotted rope 100
>Figure-of-eight 75-80
>Bowline 70-75
>Double Fisherman's 65-70
>Fisherman's 60-65
>Clove hitch 60-65
>Overhand 60-65
>
>The same percentages are given in "Climbing: The Complete Reference" by
Greg
>Child.
>
"Freedom of the Hill"s gives the same figures. They credit the American
Alpine Journal (unfortunately no full reference). That's presumably the
original source of these numbers.
Jeff
Jeffrey Mazo
I think there are two issues here. If you search dejanews (google) for
"Girth Hitch" you'll find some real data from Chris Harmston at the Black
Diamond labs, albeit tests on single samples. Two spectra slings girth
hitched together failed at 71% of rated strength. Note that the vast
majority of slings will break at a much higher strength than the rating, so
the weakening is much greater than these figures imply.
But this is for two slings girth hitched together. I think the "received
knowledge" that this knot is dangerous comes from a vague memory of this
particular situation. I would be interested in seeing data for a single
sling girth hitched over a branch, spike etc. I would guess that the
strength reduction would be a lot less than in the sling-sling scenario.
Jeff
Steve Pardoe
Many thanks for the comprehensive answers thus far... ... I think I'll keep
avoiding larks' feet (whether or "knot" in aspic, thanks).
There's some more comment below:
Martin Whittaker <martinwe...@aol.com> wrote in message
news:20010517055720...@nso-md.aol.com...
> In article <9duvot$e80$1...@taliesin.netcom.net.uk>, "Carol Haynes"
> <lairdswo...@SPAM.yahoo.ME.co.uk> writes:
>
> >I find that hard to believe - does anyone have a reference anywhere?
>
> From "The Climber's Handbook" by Garth Hattingh: "A sling can be draped
around
> a tree or through a wormhole*. However, avoid using Lark's foot
configurations
> where possible, as these can weaken the sling by up to 75%!"
>
> Now, whether you regard that reference as trustworthy is another matter,
but it
> is a reference.
Hmmm. Some of his books are sloppily edited (eg titles of mountain pictures
that are just plain wrong), but I've no idea of his technical reliability.
And I think he's South African rather that American, FWIW.
<snip>
> I wonder whether the advice against using a lark's foot in a sling is more
> relevant with dyneema slings, which are narrower and thus will exert a
greater
> pressure on the crossing point when subjected to the same shock load?
As in Carol's reference to cheesewire, of course.
> That
> would also make the lark's foot bad for rope (which is what Fyffe and
Peter
> say), but perhaps less of a problem for 25mm wide nylon slings.
Indeed.
> I'm interested in this question because I have a copy of "Climbing
Anchors" by
> John Long which specifically recommends using a girth hitch to secure some
> thread or spike anchors. While the book is generally a useful reference
on
> setting anchors and belays, when I mentioned it to another climber friend
they
> said "Oh, I wouldn't trust anything in that book because it says it's all
right
> to use a lark's foot on a sling and everyone knows that's dangerous."
Is that an American book? Perhaps it's a transatlantic thing. After all,
they clip into top-ropes with a bowline and krab (sorry, "biner") at the,
er, gym, don't they?
> Anyone else got any specific references?
>
> Martin
>
> * This is the only reference I've seen to the use of anomalies in the
> space-time continuum as protection placements!
Smart-*rse! ;-)
Steve
Crispin
> sling girth hitched over a branch, spike etc. I would guess that the
> strength reduction would be a lot less than in the sling-sling scenario.
Possibly sling-sling is better, because if (as an earlier poster
suggested) the sling gets cut by a
2-strand-on-one-strand-cheesewire-effect, this is avoided with the
sling-sling tie when the hitch 'flicks' around into a symmetrical reef
knot. In any case there will be little slippage of the knot so not much
risk of cutting.
It's the fact that it's not symmetrical when tied around a tree
(especially if there's friction between sling and tree), and also that
trees are bigger than slings so there is more slippage, that causes the
single strand to be held still while the double cuts it.
Maybe. What I'm saying is don't larks foot round a tree but it might be
alright for joining slings. (Though I've always done it with a karabiner
anyway - easier to undo).
--
Crispin
Martin Whittaker
<ste...@AMpardoes.com> writes:
>Many thanks for the comprehensive answers thus far... ... I think I'll keep
>avoiding larks' feet (whether or "knot" in aspic, thanks).
I've been doing some more thinking, reading, searching on the 'net and playing
with rope and tape slings. I've read the data on slings girth-hitched
together. I have no idea how that relates to a sling girth-hitched round a
thread anchor, but it does seem pretty clear that the presence of the knot will
reduce the overall strength of the sling. This would seem to me to be a bad
thing.
I can't see any good reason to put a lark's foot in a sling going round a good
thread anchor (tree root, "wormhole" or whatever). John Long's book suggests
that it may be useful for chockstones where you think the sling may creep
between the stone and the wall. My first thought on this is: if you believe
that the anchor may fail in this way then should you be using it anyway?
However, I played around with some slings and discovered that there is one
instance in which a lark's foot might just save your neck with a dodgy anchor
like this. If just one of the two loops of tape encircling the chockstone does
manage to creep through between the stone and the wall then the knot will drop
out and leave you with a sling looped once around the chockstone (how you
retrieve the sling from this position is an exercise left to the reader). So
you will still have an anchor, although it will give by a distance equal to
half the circumference of the chockstone at the point where the sling was
knotted round it.
However (again) there is another way to gain the same degree of security (such
as it is) without putting a knot in the sling. What you do is to drape the
sling round the anchor, then put a half twist in ONE side before clipping the
two ends together with a krab. If one loop of the sling creeps through in this
instance, the half twist causes the sling to form a double loop around the
krab, but again the anchor will still be intact. I'm not much good at
describing this stuff, you probably have to try it yourself to see what I mean.
One reason *not* to do this might be that it risks placing a three-way loading
on the krab. I think the best way to reduce this risk is to use a long enough
sling that the two ends form a very acute angle when the sling comes tight.
Also, if one side of the sling does creep through then the anchor will give by
just under half the length of the sling, which might be a trifle disconcerting
(but less so than the whole sling coming away).
Another reason John Long gives for using a lark's foot is to secure a sling on
a spike anchor, ie to reduce the risk of it slipping off the end of the spike.
In my searches on the web I came across a knot at
http://www.cavepage.magna.com.au/cave/knot.html which seems to provide this
security while avoiding the issues presented by the lark's foot. On that page
it is called the "constrictor knot". I have found that it is possible to tie
this knot in a sewn sling which you are placing over a spike (you can't do this
with a thread anchor).
Again, I can't really describe how to do it, but it involves making the sling
into three concentric loops, then flipping one of the loops over before
dropping the whole lot over the spike and pulling tight on one of the other
loops. It's a bit fiddly, and because it goes round the anchor twice it uses
up a fair amount of the length of the sling, but it does seem to be possible to
cinch it up pretty tight to stop it slipping up the spike - certainly tighter
than a lark's foot, and with none of the right-angled crossings which make that
knot so suspect. With a tape sling, it is possible to work all the twists out
so that the tape lies flat all the way round the anchor, so ensuring that any
load that comes on to the sling is broadly distributed and helping to avoid any
"cheesewire" effect.
>> I'm interested in this question because I have a copy of "Climbing
>Anchors" by
>> John Long...
>Is that an American book? Perhaps it's a transatlantic thing.
Yes, it is an american book. However, my experience is that the laws of
physics work the same way on both sides of the atlantic.
> After all,
>they clip into top-ropes with a bowline and krab (sorry, "biner") at the,
>er, gym, don't they?
I've got no problem with a properly-tied bowline, especially if the tail is
re-threaded. Actually, I think a bowline can be easier to tie than a
rethreaded figure eight.
At least one person I climb with at my local wall clips in to the top-ropes
with a figure of eight on a krab clipped in to the belay loop on his harness.
He did the same thing when we went cragging together once. He reckons it's an
Alpine thing, something to do with being able to swap ends on the rope without
untying. I don't know whether I should be discouraging this behaviour. At the
end of the day, I know I can belay his rope safely: if his attachment to the
rope fails, it's his problem. I'll still have the rope, so if I'm at the top
of the pitch I can still get down...
Carol Haynes
> In article <tg7cacp...@corp.supernews.co.uk>, "Steve Pardoe"
> <ste...@AMpardoes.com> writes:
>
> Another reason John Long gives for using a lark's foot is to secure a
sling on
> a spike anchor, ie to reduce the risk of it slipping off the end of the
spike.
Just use a clove hitch with spike anchors.
Carol
Steve Pardoe
<snip>
> Just use a clove hitch with spike anchors.
Yep.
S
Tony T
> However, I played around with some slings and discovered that there is one
> instance in which a lark's foot might just save your neck with a dodgy
anchor
> like this. If just one of the two loops of tape encircling the chockstone
does
> manage to creep through between the stone and the wall then the knot will
drop
> out and leave you with a sling looped once around the chockstone (how you
> retrieve the sling from this position is an exercise left to the reader).
So
> you will still have an anchor, although it will give by a distance equal
to
> half the circumference of the chockstone at the point where the sling was
> knotted round it.
>
Aahh. Topology. Doncha just luv it?
Möbius come home - everything's fine.
--
Tony "pissed off with my ISP and one glass of grappa too many" T
Replace the DOT for e-mail address
Rob Smith
'They (PYB) have been testing larksfoot slings to destruction & have found that
in all circumstances the carabiner failed before the sling'. I believe they
also said the only configuration where the sling came close to breaking at the
same time as the carabiner was where the larksfoot was around a large tree, if
the sling was rotated such that the load is at a tangent to the tree rather than
symetrical even this was avoided.
My conclusion is that, yes the larksfoot is weaker than other knots, but I'm
happy to use it here and using a carabiner to link the sling around a tree will
only weaken the setup as well as effectively shortening the string length.
Warning: All this is third hand & if you die don't sue me! - you may want to
see the results published before using said larksfoot etc. etc.
Steve Pardoe wrote:
<snip>
Carol Haynes
loading than slings (and are supposed to have a longer life too). If the
krabs are failing first then there is something seriously wrong with the
UIAA tests/certification, especially as destruction testing evidence has
shown that larkfooting significantly reduces the strength of a sling (what
ever figure you happen to choose)
Carol
"Rob Smith" <surnamef...@nortelnetworks.com> wrote in message
news:3B08ED04...@nortelnetworks.com...
Rob Smith
identically rated at 22kn and these are of course both 'ideal circumstances'
ratings with no knots in the sling & 2way, inline, closed gate loading on the
carabiner.
In practice the sling loses some strength because of the knot (larksfoot), the
carabiner loses some strength because it is 3way loaded when used to replace a
larksfoot around a tree. I'm sure you should be able to engineer specific
circumstance where one way is better than another but in practice the message
seems to be 'larksfoot sling is OK'.
Steve Pardoe
Oh dear!
Rob Smith <surnamef...@nortelnetworks.com> wrote in message
news:3B0912F7...@nortelnetworks.com...
> I'm not terribly surprised by this. Most of my slings & carabiners seem
to be
> identically rated at 22kn and these are of course both 'ideal
circumstances'
> ratings with no knots in the sling & 2way, inline, closed gate loading on
the
> carabiner.
A quick trawl through my own rack confirms that slings' ratings range from
14kN (on cams) to 30kN (for a big Clog sewn one). My krabs, plain and
screw, seem to range from 20kN to 27kN (all with gate closed, obviously).
> In practice the sling loses some strength because of the knot (larksfoot),
...
I think we can agree that it loses quite a large percentage.
> ...the
> carabiner loses some strength because it is 3way loaded when used to
replace a
> larksfoot around a tree.
In most cases, unless the sling is barely long enough to reach round the
fixed point, the angle subtended by the two ends of the sling should be
acute enough not to impose a significant three-way load, surely?
> I'm sure you should be able to engineer specific
> circumstance where one way is better than another but in practice the
message
> seems to be 'larksfoot sling is OK'.
OTOH...
> Carol Haynes wrote:
>
> > This is really worrying stuff ... almost all krabs are rated to higher
> > loading than slings (and are supposed to have a longer life too).
Yes, generally, but...
> > ...If the
> > krabs are failing first then there is something seriously wrong with the
> > UIAA tests/certification, especially as destruction testing evidence has
> > shown that larkfooting significantly reduces the strength of a sling
(what
> > ever figure you happen to choose)
Too much information, the bane of decision-making!
Here are some references. The (American) book which prompted my original
post was "Climbing From Gym to Crag" by S. Peter Lewis and Dan Cauthorn
(Swan Hill / Airlife Books ISBN: 1 84037 251 6) which has loads of
illustrated examples of a lark's-foot (AKA girth-hitch) used in a sling,
without any warning or qualification that I could see.
Counter to that is the following extract from "The Mountain Skills Training
Handbook" by Pete Hill MIC and Stuart Johnston MIC (David & Charles ISBN 0
7153 1091 7) which I've also found in our local library, and is endorsed by
the Association of Mountaineering Instructors. It has this to say about the
lark's-foot :
"The lark's-foot is included here, not as an essential knot but rather as
one to avoid using. It will often be deployed in situations where a clove
hitch should be utilised. The lark's-foot is a very weak knot, and it
dramatically reduces the strength of a sling when tied around an anchor. It
is also often used ill-advisedly to join two slings together, a situation
where a screwgate karabiner should be used.
"The only time that a lark's-foot should be used is to attach a sling onto a
harness to use as a safety line or 'cow's tail'. In this situation, the
sling is threaded through the leg loop and waist-belt central points, taking
the same line as the abseil loop, the lark's-foot tied and pulled in snug".
Well, I'm overloaded by all this, but my inclination remains to avoid the
lark's-foot wherever possible.
Thanks again for all the input.
Steve
r.na...@btclick.com
> Quoting from a pal currently doing stuff with PYB.
>
> 'They (PYB) have been testing larksfoot slings to destruction & have found
that
> in all circumstances the carabiner failed before the sling'. I believe
they
> also said the only configuration where the sling came close to breaking at
the
> same time as the carabiner was where the larksfoot was around a large
tree, if
> the sling was rotated such that the load is at a tangent to the tree
rather than
> symetrical even this was avoided.
>
You sure about this? Chris Harmsworth (formerly at BD in the USA) was
involved in some fairly intensive testing of "girth hitches" a couple of
years ago. The BD report indicated that girth hitched slings failed
consistently at relatively low loadings. I seem to recall that spectra
slings often showed evidence of melting at the fail point. It used to be
possible to find pointers to the BD report by a deja search on girth hitch
and chris harmsworth, but haven't tried it via google yet. May when I get a
minute.
Rob
r.na...@btclick.com
pictures and loadings that I was looking for was Karl Lew's: Chris H did the
testing, Karl put together the summaries. However, Karl's specified URL
from my google search on "girth hitch" at rec.climbing comes up as not being
available any more.
Rob
Carol Haynes
<r.na...@btclick.com> wrote in message
news:KzgO6.4031$26.39261@NewsReader...
> Why'd I say Harmsworth? It's Harmston. Sorry
It's because you were singing 'Stairway to Heaven' with a wobbleboard at the
time ;-)
Carol
Jeffrey Mazo
Carol Haynes wrote in message <9eb0m4$mig$1...@taliesin.netcom.net.uk>...
>This is really worrying stuff ... almost all krabs are rated to higher
>loading than slings (and are supposed to have a longer life too). If the
>krabs are failing first then there is something seriously wrong with the
>UIAA tests/certification, especially as destruction testing evidence has
>shown that larkfooting significantly reduces the strength of a sling (what
>ever figure you happen to choose)
>
>Carol
Not necessarily - you'd expect the majority of gear to fail well above its
rated strength. So who cares if the krabs break first, as long as they break
above their rated strength?
Jeff
Jeffrey Mazo
r.na...@btclick.com wrote in message ...
>
>You sure about this? Chris Harmsworth (formerly at BD in the USA) was
>involved in some fairly intensive testing of "girth hitches" a couple of
>years ago. The BD report indicated that girth hitched slings failed
>consistently at relatively low loadings. I seem to recall that spectra
>slings often showed evidence of melting at the fail point. It used to be
>possible to find pointers to the BD report by a deja search on girth hitch
>and chris harmsworth, but haven't tried it via google yet. May when I get a
>minute.
>
Chris's tests were of two slings girth hitched together.
Jeffrey Mazo
It still exists, its just been moved. Don't have the URL off-hand, but I
found it via the rec.climbing faq (www.tradgirl.com).
D.Virdee
Steve Pardoe quoted from a book:
>
> "The only time that a lark's-foot should be used is to attach a sling onto a
> harness to use as a safety line or 'cow's tail'. In this situation, the
> sling is threaded through the leg loop and waist-belt central points, taking
> the same line as the abseil loop, the lark's-foot tied and pulled in snug".
>
This is the only time I use a lark's foot - and I tend to use it alot if
I'm
bolt clipping (shit, what did I just admit to?) - esp. if you're making
many
rappel decents - you get to the next rap station, unclip the cow's tail
from you're
harness and clip into the lovely, shiney bolts, along with the 10 other
folk
ab-ing off at the same time!
A cowstail is a great way to secure beginners quickly on a multi pitch
route, too -
just clip them straight into the anchors - there's less (no)knots for
them to undo
when the have to start climbing - just undo do the locker, dismantle the
anchors
and up they come!
Mike
Karl's site is now at
www.putzl.com/~klew/
Mike
Rob Smith
r.na...@btclick.com wrote:
> Rob Smith <surnamef...@nortelnetworks.com> wrote in message
> news:3B08ED04...@nortelnetworks.com...
> > Quoting from a pal currently doing stuff with PYB.
> >
> > 'They (PYB) have been testing larksfoot slings to destruction & have found
> that
> > in all circumstances the carabiner failed before the sling'.
>
> You sure about this?
Nope, not until/if PYB actually publish their tests.
Denzil Broadhurst
I'm aware that people at Troll have done tests of slings using the larksfoot
round a belay point, and under shock loading have melted through the
sling quite easily. Don't have any figures to hand unfortunately. It's the
cheesewire effect as the moving part of the sling rubs against a fixed spot
on the end of the loop - rapidly overheats it.
Denzil
back2...@gmail.com
why use one when you can use a retreaded 8 on rope or a screw gate on a tape.
please use a rope protector, 1 to look after your rope 2 look after the environment we all enjoy being in
back2...@gmail.com
> Aparently, a larks foot is actually stronger than a knotted sling...MIC test
> at Plas Y Brenin or something...
>
>
> Tom
> > It is a cheesewire effect, if you think about it a larksfoot crosses a
> > single strand with a double strand. In a shock load the double strand will
> > cut the single.
> >
> > I was told that the knot can reduce the strength to 30% of the slings
> > capacity.
> >
> > Better to put the sling double round the tree and put a crab through both
> > end loops.
> >
> > Carol
> >
> > "Tony Buckley" <a.g.b...@dl.ac.uk> wrote in message
> > news:9du84t$pjm$1...@mserv2.dl.ac.uk...
> > > Steve Pardoe, for it was he, wrote asking about lark's feet (though not
> in
> > > aspic, one presumes),
> > > > Is my concern just total
> > > > b*ll*cks (TM), or is there some truth in it?
> > >
> fails'
> > > note that comes with them, it shows something about the relative loading
> > > that different configurations can bear. AFAICR, a lark's foot
> arrangement
> > > halves the loading the sling can bear. Whether this is due to melting
> or
> > > not I don't know, but it's good practice to avoid using them.
> > >
> > > Tony
> > >
> > >
> >
> >
maybe, a knoted sling only has 45-50% of the tape used!!!
back2...@gmail.com
> I find that hard to believe - does anyone have a reference anywhere?
>
> amount for rope. I'd be surprised if there is a huge difference in slings.
>
> evidence people have of this. What about sewn slings?
>
> Carol
>
> "Tom Hawkins" <vertical...@bigfoot.com> wrote in message
> news:tyCM6.21913$tU6.2...@news2-win.server.ntlworld.com...
