Author Topic: Knot to secure bear bag--a question  (Read 14810 times)

tomcohen

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Knot to secure bear bag--a question
« on: April 10, 2009, 07:04:06 PM »
We make bear bags from bullet proof fabric.  www.ursack.com.  Our new bags are closed with a 1/4" 2500 pound tensile strength cord.  Think of it as a laundry bag.  We need a knot that will be secure against bears and can allow the bag to be cinched very tight.  The best I have come up with is a shoelace knot which is then modified by threading the loose ends through their adjacent loops, and then pulling the loose ends until the knot is snug.

Two questions:  Does anyone have a name for the knot I described?  Is there a picture of it anywhere?

Does anyone have a suggestion for a better knot.

roo

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Re: Knot to secure bear bag--a question
« Reply #1 on: April 10, 2009, 07:14:29 PM »
We make bear bags from bullet proof fabric.  www.ursack.com.  Our new bags are closed with a 1/4" 2500 pound tensile strength cord.  Think of it as a laundry bag.  We need a knot that will be secure against bears and can allow the bag to be cinched very tight.  The best I have come up with is a shoelace knot which is then modified by threading the loose ends through their adjacent loops, and then pulling the loose ends until the knot is snug.

Two questions:  Does anyone have a name for the knot I described?  Is there a picture of it anywhere?

Does anyone have a suggestion for a better knot.

Have you tried this against an actual bear?  I'd think that if a knife can cut your bag or cord, it wouldn't last very long with a bear.

UPDATE:  After looking around your site, it seems that you have a spring slider on the twinned cord.  As a backup, you could tie a figure 8 stopper in the twinned cord, drawn tight against the slider.  Then to join the free ends of the cord around an object you could tie a Zeppelin Bend:

http://notableknotindex.webs.com/Zeppelin.html

Or you could use your favorite hitch to tie the cord to an object.

UPDATE 2: I should note that the side-oriented figure 8 bend (figure 8 version of the Euro Death Knot) can roll under serious load.  The figure 8 that I'm suggesting will usually (perhaps always due to the slider) be loaded like a regular stopper, though, which doesn't have this problem.

ref:
http://www.xmission.com/~tmoyer/testing/EDK.html
« Last Edit: October 28, 2009, 04:47:05 PM by roo »
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tomcohen

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Re: Knot to secure bear bag--a question
« Reply #2 on: April 10, 2009, 10:19:12 PM »
Thanks for the reply.  I should have made clear that we no longer use the slider/cord lock. We have gone to a thicker cord 1/4"+ and the cordlock is no longer necessary.  What is crucially important to us is that we can cinch the bag tight with the first overhand knot (or equivalent).  I'll try the zeppelin bend, but feel pretty sure that the euro death knot will not work because it would be too hard to cinch the bag tight.

We have been in business since 2000 and tested out bags more than a dozen times at the zoo and many more times with actual campers and actual wild bears.  The thinner cord was never chewed through.  Our newer thicker cord has the same tensile strength, but does not have a kevlar/technora core.  We don't see this as a threat--we learned long ago that a bear has dull teeth and a strong jaw.  Rodents can occasionally chew through the cord, but never a bear.

roo

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Re: Knot to secure bear bag--a question
« Reply #3 on: April 10, 2009, 10:44:23 PM »
Thanks for the reply.  I should have made clear that we no longer use the slider/cord lock. We have gone to a thicker cord 1/4"+ and the cordlock is no longer necessary.  What is crucially important to us is that we can cinch the bag tight with the first overhand knot (or equivalent).  I'll try the zeppelin bend, but feel pretty sure that the euro death knot will not work because it would be too hard to cinch the bag tight.

We have been in business since 2000 and tested out bags more than a dozen times at the zoo and many more times with actual campers and actual wild bears.  The thinner cord was never chewed through.  Our newer thicker cord has the same tensile strength, but does not have a kevlar/technora core.  We don't see this as a threat--we learned long ago that a bear has dull teeth and a strong jaw.  Rodents can occasionally chew through the cord, but never a bear.

No slider?  That's too bad.  Maybe you can have both ends emerge from a single grommet, instead, and then use the twinned cords in a Figure 8 Stopper.  You shouldn't have to squeeze the last 0.001 inch from the opening.  Your goal should be having a knot that will resist opening and can be loaded in multiple load paths without moving and without jamming (becoming difficult to untie).

If the bag is pulled while attached to a branch, the Figure 8 Stopper will be equally loaded on both ends, like a stopper in a taut rope.  This is a well-tested mode of operation that should be OK to untie and won't cause movement.

If the bag mouth tries to expand, the twin lines going through the grommet will load the Stopper, well... like a stopper.  Again, this is a well-tested mode of operation that should be OK to untie and won't cause appreciable movement.
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tomcohen

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Re: Knot to secure bear bag--a question
« Reply #4 on: April 10, 2009, 11:00:15 PM »
We have to make this work when not tied to a branch.  We used to emerge from asingle grommet, but we can cinch the opening tight enough this way.  If there is any slack, the bear can force its muzzle into the bag and extract some food.  I am pretty sure that the first part of any knot we use has to be an overhand knot.  A square knot will work in most instances, but a persistent bear could eventually work it open.

roo

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Re: Knot to secure bear bag--a question
« Reply #5 on: April 10, 2009, 11:30:41 PM »
We have to make this work when not tied to a branch.  We used to emerge from asingle grommet, but we can cinch the opening tight enough this way.  If there is any slack, the bear can force its muzzle into the bag and extract some food.  I am pretty sure that the first part of any knot we use has to be an overhand knot.  A square knot will work in most instances, but a persistent bear could eventually work it open.

Instead of "overhand knot", I think you mean the initial tuck of a reef knot.  The difficulty with a reef knot is that it's not stable in other loadings, for example when one of its free ends are pulled.  This may be partially avoided by finishing the reef knot with another (third layer) tuck.

I would like to think that there might be a cleaner and more solid solution, though.  Anyway, per my previous post, if you use your X-ray vision to see through the neck of the bag, a Figure 8 Loop can be made small enough to prevent a bear nose, even after the knot has be strained, although it admittedly may not be easy enough to do for everyone.

I'm sure there's room for improvement.
« Last Edit: April 10, 2009, 11:31:43 PM by roo »
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roo

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Re: Knot to secure bear bag--a question
« Reply #6 on: April 10, 2009, 11:57:49 PM »
You may be hestitant on this because it changes the design of your bag, but maybe you could eliminate the internal lacing, and just use a Constrictor Knot or a Boa Knot around the neck of a slightly longer bag.

http://notableknotindex.webs.com/boaconstrictor.html

When the Constrictor or Boa Knot is tied around flexible material, it can often be more easily untied by bending the flexible material so that the knot form is inside the elbow.  This allows some slack to be introduced into the knot.

If you are overly worried about the binding cord eventually sliding off the end, you could sew a chunk of plastic in a pouch near the binding.
« Last Edit: October 28, 2009, 04:46:33 PM by roo »
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Sweeney

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Re: Knot to secure bear bag--a question
« Reply #7 on: April 11, 2009, 08:03:33 AM »
This may be a bit clumsy though not difficult - tie a reef or square knot to cinch the bag tight and then take each end and tie a half knot around the standing part close to each side of the square knot to lock it (in effect a Fisherman's knot with a square knot in the middle). I'm sure a bear workig for long enough could loosen any knot but this might be worth a try.

Barry

tomcohen

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Re: Knot to secure bear bag--a question
« Reply #8 on: April 12, 2009, 01:27:08 AM »
I like the square knot plus fisherman's knot idea.  Now it needs to be translated into plain English aimed at the lowest common denominator campers.  How do you describe a fisherman's knot in plain terms?

roo

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Re: Knot to secure bear bag--a question
« Reply #9 on: April 13, 2009, 04:59:01 AM »
.  Now it needs to be translated into plain English aimed at the lowest common denominator campers. 

Along those lines, would a hefty zipper and a clip/carabiner work?  It doesn't need any explanation.
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trade use only

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Re: Knot to secure bear bag--a question
« Reply #10 on: April 13, 2009, 08:24:34 AM »
A Fisherman's Knot has the advantage of being really easy to remember
when you've tried it only once.  Just what you need.
And it's really easy to describe.

Because it comprises two Overhand Knots working together.
An incredible result from applying what anyone (!) knows how to do -
tie an Overhand Knot...

Try this to get the idea of teaching it
http://www.troop7.org/Knots/Fisherman.html

To get neatnest appearance, when you start with two lines with ends
lying side-by-side overlapping, if you start the first overhand knot
going over the adjacent rope, when doing the other end also start by
going over the adjacent.  Or under and under.  Then the two knots
snuggle together.  Anyone will be proud of the ability to do this neat
knot and will remember it well.  But that neatness isn't a necessity
to obtain the functionality you require.


Also, "over and over" or "under and under" is the simplest way (?) to
remember how to do the reef knot ("square knot") correctly.  You do need
to know a rule with this effect to avoid ending up with a much less
secure knot (typically the unfortunate "Granny Knot").

So the user will remember the rule, sparkling and clear, because they
are using it twice.  They'll feel like experts and, well - why
not...?!

roo

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Re: Knot to secure bear bag--a question
« Reply #11 on: April 13, 2009, 02:48:15 PM »
A Fisherman's Knot has the advantage of being really easy to remember
when you've tried it only once.  Just what you need.
And it's really easy to describe.

Because it comprises two Overhand Knots working together.
An incredible result from applying what anyone (!) knows how to do -
tie an Overhand Knot...

Try this to get the idea of teaching it
http://www.troop7.org/Knots/Fisherman.html



While I'm not sure what Sweeney means by "half knot", the problem with using an acutal fisherman knot structure is that if the bear pulls on a cord end belonging to the fisherman knot, it'll jam it.  That's a possible problem too with the Figure 8 solution.   Maybe it's not a big deal if you're willing to cut your knot free.
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Sweeney

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Re: Knot to secure bear bag--a question
« Reply #12 on: April 13, 2009, 05:41:28 PM »
For the record by "half knot" I meant an overhand knot around the standing part. Although there is a fisherman's knot here it is split into 2 parts by having the square knot in the middle and is therefore a bit less likely to jam - if this is a problem a simple half hitch may suffice if pulled tight against the square knot at each side. Another thought for what it's worth - use the cord with a square knot as now but first add a nylon cable tie running through the same channel as the cord. This will need to be cut off to open the bag but they are cheap, don't take up much room and weigh very little as well as being very strong and simple to use (perhaps when the risk is greatest?). A bit of heresy for a knotting site!

Barry

Dan_Lehman

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Re: Knot to secure bear bag--a question
« Reply #13 on: April 14, 2009, 07:29:07 PM »
... .   We need a knot that will be secure against bears and can allow the bag to be cinched very tight.
...
Does anyone have a suggestion for a better knot.
A quick suggestion is to use a Rolling Hitch of one end around the other.

--dl*
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Dan_Lehman

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Re: Knot to secure bear bag--a question
« Reply #14 on: April 14, 2009, 07:52:15 PM »
A *slower* suggestion is to use Ashley's #1029 eyeknot,
used as the alleged "Crabber's Eye Knot" was supposedly used:
put into position and then drawn tight to lock (here, "into position"
would mean drawing the bag tightly closed).

I believe that an effective method for tying this would be to
(1) have a stopper knot (Ashley's is a good one!) in the short
end (yes, a length bias is wanted; as with the Rolling H. tie-off),
and after making an initial closure of the bag
(2) form an Overhand knot in the long end near to the opening;
(3) then reeve the stoppered end through this (if not otherwise
tying that Overhand around the short end folded into a bight),
and finally (4) haul on the short end to close the bag more,
and then (5) haul on the long end and press/capsize the Overhand
into locking form.

Which all sounds intimidating, but it's more bark than bite, really.
The Ashley's stopper in the short end has two functions:  most
important is to prevent the end--since it's short--from being drawn
into the bag hem; and it should also give good purchase for Step
#4, hauling this end to close the bag more.

Step #5 isn't so much; the capsizing, such as it is, is simple.
The S.Part's Overhand will need to be moderately open/loose
in order to accommodate the reeving of the stoppered short end
through it to form #1029, but might then be worked a little
tighter; and then hauling on the short end will straighten that
and enable further bag-closure tightening.  An ultimate setting
of the knot should give back a bit of this tightening--pulling on
the part running opposite to the short end into the bag, i.e.--;
but it will still be well closed.

This knot structure has an attractive mutli-directional ability.
(It's one I'm working into use with an ELETriangle anchoring
structure (rockclimbing).  It's a fair replacement for a Sheet
Bend / Becket Hitch.

Thus, the long end is well defined to be loaded and effectively
turning the closure (which is a bend in load profile) knot
into an eyeknot (as is #1029).  NB, the short end (the end of
#1029) can go in either direction of its bight (i.e., go in at point
A & out at B, or vice versa--the right-handed/left-handed bowline
or sheet bend aspect)).

TO LOOSEN THE KNOT for untying:  pull the short end
away from itself (i.e., it is in two legs of a bight, so knotted;
pull these apart).  This action should draw in some material
from the S.Part or other end, adequate to enable loosening
and untying.

--dl*
====
« Last Edit: March 19, 2010, 06:27:47 PM by Dan_Lehman »