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Old 30-05-2013, 07:42   #76
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Re: In defence of the sheet bend

My cat can undo a sheet bend. Just sayin'.
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Old 30-05-2013, 08:03   #77
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Re: In defence of the sheet bend

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Originally Posted by estarzinger View Post
By the way . . . . one more thing to mention is cleating off bare dyneema single braid. I am using a tug boat hitch (which is quite easy and simple and appears not to slip) rather than the conventionally 'yachty cleating pattern' which appears to very very slowly (a couple inches per day) slip when under decent cyclic loading.
Sounds familiar, some friends do high speed winch systems using tech12, similar to dyneema sk75 etc, they had real problems terminating the rope inside the winches with the same problem, very slow creep. In the end cast the line into epoxy to create a termination.
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Old 30-05-2013, 08:58   #78
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Re: In defence of the sheet bend

G'Day all,

I'm interested in the condemnation of the lowly bowline, apparently due to its tendency to "shake loose". We, and very many others, have used bowlines to attach jib sheets to clews for years. I can not think of an application which would subject the knot to more shaking, frequent slacking to zero load and general abuse... yet I have never had one come loose.

Could someone explain this apparent paradox?

Cheers,

Jim
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Old 30-05-2013, 09:12   #79
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Re: In defence of the sheet bend

A bowline will shake loose if the tail is too short. It wants 3" minimum.
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Old 30-05-2013, 09:14   #80
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Re: In defence of the sheet bend

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I was thinking some more on why the double fishermans might have failed so quickly in my test, and this would imply that the triple would be as bad or maybe even worse. The problem seems to be that the loaded part of the rope is buried and well insulated inside the knot, so any heat generated by friction and elasticity is trapped, building up until it melts. the heat must be large as it melted the cover of the kernmantle rope we were testing.

Knots like the sheet bend have the loaded part more on the outside where any heat buildup can escape. unfortunately I didn't test a sheet bend. But the bowline held up much better than the double fishermans bend.
Hi Stormpetrel
The triple need not necessarily be worse, as the mechanism may alter when the distance to the first curve in the knot increases. I came across this observation in T. Moyer et al's 2000 report on testing of high strength cord:

"For a double fisherman's knot, Gemini and Titan share an interesting failure mode. The sheath breaks at the knot and the slippery core unties, pulling through the sheath. When a triple fisherman's knot is tied, this does not happen. The strength gain for the triple fisherman's is not large, but it is enough to change the mechanism."

This was not noted for the 7mm nylon they tested (I think that was kernmantle, but it is not clear), but this may alter as the diameter of the line changes (what diameter kermantle did you use and was it new line?).

To save you looking it up, the Gemini they refer to has an aramid core & polyester sheath and the Titan a UHMWPE/nylon core and nylon sheath (Dyneema which is 100% UHMWPE was not tested).

It was really interesting to read that when a Figure Eight knot was tied the tensile strength decreased by 47% for the UHMWPE/Nylon line, but only 8% for the nylon line.

When a loop was tied using a double fisherman's, the UHMWPE/Nylon loop only had 65% of the tensile strength of the nylon loop.
(The tensile strength of the 5.5mm hybrid UHMWPE/nylon they tested was about 10% greater than the 7mm nylon to start with).

The Triple Fisherman's knot added nothing to the strength of the nylon loop compared to the Double Fisherman's, but increased the strength of the UHMWPE/nylon by about 20% . So it is may be worthwhile adding an extra turn when using Dyneema.

It was be great to see some testing of Dyneema with a variety of bends in loops, including testing of various severities in the radius of the peak of the loop. Anyone with access to equipment?
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Old 30-05-2013, 09:18   #81
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Re: In defence of the sheet bend

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Presumably this was TIC however for the less knowledgeable, "defence" is correct unless you are USA indoctrinated
Ouch. Tongue in cheek, indeed.

For the record, in terms of indoctrination, I read for the doctorate in the UK.

Feel glad we aren't spelling it "defenze."
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Old 30-05-2013, 09:28   #82
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Originally Posted by Jim Cate View Post
G'Day all,

I'm interested in the condemnation of the lowly bowline, apparently due to its tendency to "shake loose". We, and very many others, have used bowlines to attach jib sheets to clews for years. I can not think of an application which would subject the knot to more shaking, frequent slacking to zero load and general abuse... yet I have never had one come loose.

Could someone explain this apparent paradox?

Cheers,

Jim
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Old 30-05-2013, 09:29   #83
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Re: In defence of the sheet bend

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My cat can undo a sheet bend. Just sayin'.
Any cat can. A really talented animal can shake out a carrick bend as well.
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Old 30-05-2013, 09:37   #84
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Re: In defence of the sheet bend

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Originally Posted by Jim Cate View Post
Could someone explain this apparent paradox?

Cheers,

Jim
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Old 30-05-2013, 09:56   #85
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Re: In defence of the sheet bend

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PS: The carrick bend, I have come to think, is pre-eminently suited to large stiff hawsers. Does anyone else share this feeling?
While the carrick bend indeed seems better suited to hawsers, I have read that when a carrick bend collapses on more flexible line it will still be secure. No doubt its load-carrying capacity will diminish at this point, but it should still be a stable knot.
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Old 30-05-2013, 10:02   #86
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Re: In defence of the sheet bend

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Originally Posted by Jim Cate View Post
G'Day all,

I'm interested in the condemnation of the lowly bowline, apparently due to its tendency to "shake loose".
I know the climbers simply don't use the bowline. They use the figure 8. One big difference between the climbing and sailing use (like for the jib sheet) is that we tend to progressively load up our knots, while climbers tie their knot (to their harness) and then it must hold an enormous snatch load the very first time it is loaded (if the lead climber falls). So, I suspect it is that the bowline is more reliable with 'progressive' loading and less reliable in that first single massive shock load.

Sailors also want their knots to be easy to untie even after big loads. That's a bit less important for climbers.
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Old 30-05-2013, 10:11   #87
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Re: In defence of the sheet bend

I disagree with the assessment that an Alpine Butterfly is a difficult knot to tie.

For the bend, the hand-wrapped style allows you to quickly tie two lines together.

Here are a couple of references. There is an even easier way to perform the hand-wrapped join (close to how they create the loop in the YouTube video).


Alpine Butterfly Bend | How to tie the Alpine Butterfly Bend | Climbing Knots

Heres a good one that taught me a couple:
Bends

Why I like the alpine butterfly so much is because you have the ability to create 3 three different knots with only one technique.
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Old 30-05-2013, 10:13   #88
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Re: In defence of the sheet bend

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I know the climbers simply don't use the bowline. They use the figure 8.
I went through a NOLS instructor course back in the early 70's, when the bowline was still taught to climbers. One of the reasons it fell out of favor was that it was too easy for a student to tie incorrectly, unlike the figure eight. Any novice can see when a figure eight is tied correctly, but a messed-up bowline doesn't show itself as readily.
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Old 30-05-2013, 10:22   #89
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Re: In defence of the sheet bend

I still use "the lowly bowline" all the time for all sorts of things, and it rarely shakes loose as long as there is some load on it. If I am worried about its security in some critical situation I just tape the end to the standing part. I also sometimes take a couple of turns through the eye in order to spread the load out further--in other words, a bowline with two round turns. You can do that with a lot of hitches, like is done with the anchor bend, to spread the load out.
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Old 30-05-2013, 10:31   #90
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Re: In defence of the sheet bend

In the late 70's, I experienced a bowline come loose when a skipper I was crewin' / racing for shared it over another boats line tied to a post. We went inside to a grill to have lunch and his boat got loose and slammed into another guys yacht. Damage and screamin back and forth the whole thing. Not sure one side or another of the knot is better (facing down), but it does cross my mind every time I tie up, and I consciously try to keep the better of the knot facing a direction that is 'public'. Could be myth though.
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