Cow hitches effect on MBS?

[Ledburyjosh]

Does anyone have any data or links to break tests of a cow hitch compared to single strand MBS?

 

For an example if a single strand is rated 10kn, and you tie a cow hitch, does this half it to 5kn, or initially double it for two strands, 20kn then half that so your back at 10kn?

[Canal Navvy]

http://www.hse.gov.uk/research/rrpdf/rr668.pdf

 

Well worth a look 🙂

[peds]

1 hour ago, Canal Navvy said:

http://www.hse.gov.uk/research/rrpdf/rr668.pdf

 

Well worth a look 🙂

 

That's not loading for me, could be an issue at my end though... anyone else?

 

There's definitely specifics with different knots, some are more kN hungry than others, but I always just say 50% for any knot for simplicity of maths, and to make sure any sums give an answer firmly on the safe side, rather than the dodgy side.

 

So yeah, a doubled single strand will be back at single single strand strength after both have been knotted.

One question to consider is... is whatever you're doubling for redundancy's sake really worth doubling? For ropes and soft goods the answer is often yes, for metal it's often no, and there are intricacies and exceptions all over the shop. 

[Ledburyjosh]

6 hours ago, Canal Navvy said:

http://www.hse.gov.uk/research/rrpdf/rr668.pdf

 

Well worth a look 🙂

Thanks, that does cover it. It also shows a wide range of results so lacking accuracy, which in its self may be realistic. It states a reductions in % but I can't make out what the baseline for that is, I assume single strand MBS. 

 

4 hours ago, peds said:

 

That's not loading for me, could be an issue at my end though... anyone else?

 

There's definitely specifics with different knots, some are more kN hungry than others, but I always just say 50% for any knot for simplicity of maths, and to make sure any sums give an answer firmly on the safe side, rather than the dodgy side.

 

So yeah, a doubled single strand will be back at single single strand strength after both have been knotted.

One question to consider is... is whatever you're doubling for redundancy's sake really worth doubling? For ropes and soft goods the answer is often yes, for metal it's often no, and there are intricacies and exceptions all over the shop. 

The thing with a cow hitch is its doubles hut only one is being loaded, so in unsure what applies. It would be great to see some break tests but ai cannot find any online at present.

[peds]

Oh you mean the other strand coming out of the cow hitch knot? Yeah, that doesn’t count at all, that's not doubled. It's just dead rope. I thought you meant two hitches on two single strands. 

 

You probably know about this crowd already, but they've got the biggest library of destruction testing vids I think.

 

 

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[peds]

 

 

15 minutes of breaking girth hitch/larks foot/cow hitch.

 

 

Edit:

I have to say... are you sure a girth hitch is the best knot for your intended use, if you are only weighting one strand? They are more commonly used in closed loops, where both legs get weighted equally anyway...

Seems like there's a strong risk of the knot pulling through when weighting a single leg, unless you tie off the other side of it or add a stopper knot...

Would a barrel knot work better for you?

Edited Monday at 15:15 by peds

[Ledburyjosh]

Yeah the cow hitch is a pretty common method. This is for tying deadeyes with rings/pulleys for rigging

[Dan Maynard]

5 hours ago, peds said:

Seems like there's a strong risk of the knot pulling through when weighting a single leg, unless you tie off the other side of it or add a stopper knot..

It goes twice completely around the trunk so chance of it pulling through is nil. 

[peds]

Groovy, thanks dudes. I've only ever seen it in mountaineering, usually attaching a lanyard or cow's tail.

Still definitely only the one strand weighted, anyway.