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baker_bc

joining dissimilar diameter ropes

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I have had real good results with joining dissimilar ropes. The tests I have seen show that it is plenty good. But as noted it is way important to knot the ends of your ropes. I have one occasional partner that insists on tyeing the other end as well. Often when you get down the ends are as many as 10 15 feet apart. Personally I do not like the tyeing of the rap ends together. Serious tangleing challenges often follow.

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If the knot is moving while the knot is under load and there happens to be a convenient crack waiting, it could jam.
Seems pretty unlikely. I have never seen, or even heard of, this happening. Seems that if this were going to happen, it would also happen when you went to pull the rope.

 

But if the knot moves very much you've got other things to worry about, like rapping off the end of your rope.
Agreed. Note that knot creepage can be reduced by breaking harder on the skinny rope than the fat rope.

 

Anyway, if you are doing multiple rappels, it is most convenient to alternate which rope is through the anchor. To always have to put the fat one through, would be a pain in the neck.

 

Agreed.

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The take-home message is, the EDK is the fastest way to join two rappel ropes (even of dissimilar size) and it is the best knot for avoiding stuck ropes.

 

I would be curious to hear from anyone who has joined a REALLY skinny cord (5-6mm) with a lead line for a rappel about what knot they used and if they noticed any problems.

 

 

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You can avoid the whole issue by climbing with double or twin ropes instead of that retarded "lead rope and a tag line" combo. But you might have to belay with a real belay device then instead of a GriGri :laf:

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If you're gonna use a really lightweight line for retrieval, there's something else easy you can do.

 

Thread the end of the rope through the anchor.

Tie a figure eight on a bight at this end of the rope.

Clip a biner through the loop.

Clip the biner around the hanging end of the rope. Now the rope is anchored to itself.

Tie the retrieval cord to the biner.

 

Now when you pull the retrieval cord it pulls the biner, and the free end of the rope feeds upward through the biner. The whole mess falls down on you like you would expect.

 

'Course I've never done it before but it works great in my head...

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I would be curious to hear from anyone who has joined a REALLY skinny cord (5-6mm) with a lead line for a rappel about what knot they used and if they noticed any problems.

 

We joined 6mm static cord with a 10.2 mm single rope using a triple fisherman knot. We had no problems, other than a single stuck rope (caused by the knot creeping into the rap ring and sticking). We alleviated this problem on subsequent raps by placing the knot on the other side of the anchor (i.e. pull skinny) so that the knot would creep away from the rings instead of into them. The knot crept about 12-16 inches per rap, despite best efforts to prevent it.

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I like to use a splice....if you're going to do something....do it right says I. After years of practice aboard the whaling fleet....I can do a decent splice in nigh on 3 hours now. Arrggg.

 

 

splice.gif

 

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If you're gonna use a really lightweight line for retrieval, there's something else easy you can do.

 

Thread the end of the rope through the anchor.

Tie a figure eight on a bight at this end of the rope.

Clip a biner through the loop.

Clip the biner around the hanging end of the rope. Now the rope is anchored to itself.

Tie the retrieval cord to the biner.

 

Now when you pull the retrieval cord it pulls the biner, and the free end of the rope feeds upward through the biner. The whole mess falls down on you like you would expect.

 

'Course I've never done it before but it works great in my head...

 

I'm not sure I'm visualizing this right, but I can't see how this system is an improvement. It seems to me the figure 8 on a bite is more likely to jam or snag something than a double fisherman. Also, there would be more friction in this system (i.e. you'd have to pull harder to get your rope down).

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plus, I'd worry about crossloading the biner against the anchor.

Edited by robmcdan

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I'm not sure I'm visualizing this right, but I can't see how this system is an improvement. It seems to me the figure 8 on a bite is more likely to jam or snag something than a double fisherman. Also, there would be more friction in this system (i.e. you'd have to pull harder to get your rope down).

 

Yeah, the figure eight/biner might get caught on stuff. But putting a 5 mil line through your belay device is also not really going to work, right? It seems like either way you're going to have to rap off a knot jammed in the chains. I think the eight is less likely to get caught in a link than a double fish. And that is putting aside the question of whether a 10 mil/5 mil double fish is trustworthy.

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I like to use a splice....if you're going to do something....do it right says I. After years of practice aboard the whaling fleet....I can do a decent splice in nigh on 3 hours now. Arrggg.

 

 

splice.gif

 

The first illustration looks like giant squids mating 8D

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It is a sick puppy that gets into watching squid mate. Just how is that you know what that looks like?

 

Inquiring minds want to know. :D

 

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Setting aside that fact that we are talking about knots and not splices, Ketch has provided us with the procedure for splicing twisted strand ropes. There is an entirely different method for splicing kernmantle ropes.

 

The standard method and the easiest results in a splice that is bulkier than the rope and would jam in a belay device other than a figure eight. The splice is very strong however.

 

There may be splices that are less bulky than the one I am thinking of but I'd worry about strength. If I had a brand-new rope get chopped like MCash, I'd be sorely tempted to try splicing it, but there is zero data on this in climbing ropes. Or is there...

 

Constant Diameter Splice

 

"Constant diameter splices, which reduce the diameter of the crossover area to approximate the ropes actual diameter, will significantly reduce strength performance. Please contact a qualified rigger for assistance."

Edited by catbirdseat

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Hey now carefull. There needs to ba disclaimer. I provided no help on the splicing, only in the mating of squid. Don't you love the interweb? I have been to many a rigging workshop and somehow the relationship between a long splice and the mating of squid never came up.

 

CBS is right though. a constant diameter splice will cause a large reduction in strength. Also the resultant lump in the rope would hang up in this use. Much better just to stick with an EDK or double fish. As to the previous comment about the viability of large differences. A double fishermans (or a triple) are essentially indepensant knots jammed aginst each other to provide a form of lock. As long as the twist of the knot wer correct for each other it should still be locking despite large differences. I have not seen any test on this though.

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Ok. I haven't had this issue so I have done some more research because I'm confused by a few of the posts. From what I've found out, if you put the fat rope through the anchor (pull the skinny), the stretch from the skinnier rope will cause the knot to move towards the rap ring/biner - not the other way around. Even so, it's suggested that this is still preferred over putting the skinnier rope through the anchor, especially if you're just running through a piece of webbing (heat from the movement). Anyhoo, that's according to Craig Leubben in "How to Rappel" and after talking to a few of my more experienced climbing partner. Not sure it's that big of an issue but since it was brought up...wanted to get the "skinny" on it :) Seems some of your real world experiences suggest otherwise though.

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You got it right. I said I had it bass ackwards, didn't I?

 

After that it was mentioned that it is not always very practical to insist on having the fat rope through the anchor.

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The EDK has a straight profile on one edge. The idea is that when the knot catches on an edge of some kind, it will flip out of the way allowing the straight side of the knot to pass the obstruction.

 

One_Sided_Overhand_Bend_WPK.JPG

 

It is no better in cracks.

 

Am I going blind, or is the 'EDK' just an overhand knot?

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I like to use a splice....if you're going to do something....do it right says I. After years of practice aboard the whaling fleet....I can do a decent splice in nigh on 3 hours now. Arrggg.

 

 

splice.gif

I think you should see how long it takes to splice 2 kernmantle ropes together. Shouldn't take any more time than 2 laid lines, right? ;)

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The edk is an overhand knot. With a short tail the knot can "roll" and it can become a death knot. With a long tail it is merely an overhand knot that will fulfill all of your needs.

 

 

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I have read a few things about joining ropes of different diameter and some guidelines around the various size ratios.

 

When joining ropes of different diameters >4mm it is best to use interlocking figure-of-eight-on-a-bight.

IMGP4057.JPG

 

Ropes diamter differences ~2-2.5mm it seems acceptable to join them as though both ropes are of the same diameter. However, knot selection seems key. Double and Triple Fishermans' are very strong but we all know the fun and ease that they untie with. A re-woven figure eight has plenty of strength for this application and has increased ease of untying.

IMGP4054.JPG

Extending the tails of any joining knot seems to be key. A meter of tail has room for the EDK knots (overhand or figure-eight) to flip over a few times and still have a measure of safety. Dressing and setting these slow the process.

 

Here is another picture of the 5.5mm retrieval cord and 10.5mm climbing rope rappel set up. In practice it is desireable to have the climbing rope extend down from the anchor node ~1m of avoidance room of the potential of fouling the line. The locking biner clipped through the loop and around the long line creates a closed loop so if the retrieval cord is defeated.

IMGP4063.JPG

I have used this setup since the mid 90's and have not had an issue with the joining knot becoming set in a crack. It has cut through the snow on the lip of an edge and become stuck but any rope would have been stuck. When prussiking up to the anchor it was very bouncy as the majority of the load appeared to be on the single fat line. In one case it snowed white fluff on me as the core was being cut over an edge but that just came with using a low-impact force 9.5mm rope as the mainline.

Edited by blueserac

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