Author Topic: Tarbuck vs. Modified Tarbuck Knot  (Read 299 times)

Trakl

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Tarbuck vs. Modified Tarbuck Knot
« on: May 29, 2019, 07:41:58 PM »
I am interested in finding out if Robert Chisnall's modified Tarbuck knot overcomes the negative aspects of stripping the outer sheath of kernmantel ropes that the original Tarbuck knot is the cause of.  Budworth says that Chisnall uses the modified version for securing Tyrolean traverses and in other anchoring applications.  In regards to the wonderful paper by Mark Gommers titled Knots Study Guide, would the modified Tarbuck work in place of the strangled double overhand knot in the Multi-wrap Capstan hitch?  My thanks for anyone who can provide insight into these questions.
« Last Edit: May 31, 2019, 03:00:08 AM by Trakl »

Dan_Lehman

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Re: Tarbuck vs. Modified Tarbuck Knot
« Reply #1 on: May 31, 2019, 01:59:10 AM »
'ChisnEll' => 'Chisnall'
"Robert" => "Rob"   (--bit less common, methinks.)

How could it be less injurious --the gripping/stripping
coil is the same.
(And the late Bob Thrun said that he could see that
the supposed advantage of the knot wasn't physically
possible; but I never got him to try to explain why.)

Any gripping coil loaded on the *away* side (such
as this knot, in contrast to the klemheist / Blake's
(Prohgrip) hitches
) is going to bring such injurious
forces to bear.  The loading like "finger trap" is better.
--dl*
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Trakl

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Re: Tarbuck vs. Modified Tarbuck Knot
« Reply #2 on: May 31, 2019, 02:13:41 PM »
Dan,

Thanks for catching that spelling mistake, my apologies to Rob.....i corrected it straight away.

The modified Tarbuck does seem to keep the first turn open a bit more due to the way the knot is finished.  I scrutinized both knots under strain, but that is perhaps a moot point in regards to an end knot application for a climber's tie-in.  I was more interested in why Rob Chisnall liked to use it in anchoring applications.  It seems as though it might be placed between the Tensionless Hitch with the 3 wrap prusik plus carabiner, and the simpler version using the strangled double overhand knot.

Dan_Lehman

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Re: Tarbuck vs. Modified Tarbuck Knot
« Reply #3 on: May 31, 2019, 08:11:56 PM »
I was more interested in why Rob Chisnall liked to use it in anchoring applications.
It seems as though it might be placed between
the Tensionless Hitch with the 3 wrap prusik plus carabiner,
and the simpler version using the strangled double overhand knot.

I've not checked details to what you refer re anchoring, [1]
but one potential issue with the tensionless h. is that
of rotational force on the object, which the simple non-knotting
of the basic version won't address.  By using a gripping
hitch on the tail, one thereby does *violate* the "tensionless"
aspect --which only makes sense in reference to the tail--
by giving tension to it.  The tail's tension though will likely
not need to be fully equal that of the SPart, in preventing
rotation --otherwise, it's there to arrest it.

(I don't know of any studies on this issue.)

[1] Okay, reading Mark's paper, I see his two tie-off
methods.  I suggest to these that one might simply
make a turn around the TH's SPart running back
around to then tie off w/2 half-hitches (clove)
where the finish is with a slip-knot (i.e., this
would serve qua stopper against the 2nd HH
and the slipping tail would undo both stopper
& 2nd HH if pulled).

With stiff rope, one can find some things not so
easily done.  Mark thus shows flexible thinner
rope with the Prusik h. coming to the rescue
for the stiffer main rope.  (The knotted 'biner
might be omitted for a sheet bend variant,
to spare resources.


--dl*
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« Last Edit: May 31, 2019, 08:30:59 PM by Dan_Lehman »

Dan_Lehman

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Re: Tarbuck vs. Modified Tarbuck Knot
« Reply #4 on: May 31, 2019, 08:56:33 PM »
Whoa!!! 
>>>> Okay, reading Mark's paper, I see his ...

Purcell Prusik wrongly indicating where the
"three offset coils" are (p.53 of 66).  The image
on the LEFT is the "correct" version but the black
coil-indicator points to the wrong coils --it should
point as does the right-hand side (and that one
should be changed to point as does the left ...).
(Which then matches the orientation shown in
yellow rope on previous page.)
AND, the wording is wrong to say "towards" vs.
"away".  (I wasn't sure where the harness came
'til looking again where Mark has it, in the formed
adjustable EYE end.)  Again, see the yellow rope's
knot.  The coil that grips surely --one w/more turns--
should be oriented to grip LIKE BLAKE'S/ Klemheist,
in what I call "coil away" (from anchorage); this
coil will take some room along gripped rope to
extend & grip --and so will press & push against
the mirroring coil.

Is the double coil even needed?  --or why not use
a full / equal triple coil on both sides (which then
prevents any confusion) ?!
(On Rope 2nd ed. confused --turned upside-down--
images of a completely *offset* Prusik (i.e., it had
just a turn, no round turn, on one half) and thus
got hitches that pretty much will NOT grip, but
slide.)


--dl*
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