Bobbin bunches a sheath

[Scott McCrea]

Originally published in the October 2005 issue of NSS News (vol 63, #10). Posted here with permission from the author.


Another Bobbin Issue Diagnosed

By Andrew Howe NSS #49198

I recently did a 259 foot drop on an easy bend rope with my bobbin and experienced an issue I felt should be reported to all. I’ve previously done even longer drops (350’) on my bobbin without any issue besides having to feed the rope, so I didn’t think much of doing this drop.

What happened was the sheath got pushed down the rope making the rope fatter. I was the third person down and the sheath had been pushed down enough to make it too thick to feed through my bobbin. This occurred at perhaps the midway point or just below it.

Once I recognized what was slowing then finally halting my descent, I was able to stretch out the sheath beneath me, thus allowing the short section of tightened rope to feed properly. The process was: push the sheath, then feed the rope through the bobbin. However, in my case, by the time the problem was bad enough to halt my descent, little feeding was necessary.

Part of the problem was also due to the spools on my bobbin. They are very well used and thus the grooves are rather deep. As one might imagine, they are only the width of a tightened rope, thus they created a bottleneck for the fattened rope.

This was not a problem with subsequent descents that day on shorter rope, so the spools themselves are still completely functional on tight rope.

If one knows they will be doing a long single drop on a rope that has the potential to have the sheath bunch up, they should consider using fresh spools in their bobbin. But be careful on your new spools: fresh spools won’t have as much contact with the rope and therefore will have less friction, so the bobbin will be much faster on rope than you’ve grown accustomed to!

Of course, a rack is much better on descents like this one, so the better practice would be to avoid bobbins in long drops altogether.



Personally, I have never heard of this happening. Cheers to Andy for sharing his experience.

[hank moon]

i've had this happen before, but only on one type of rope. excess sheath slippage is mostly a rope problem imo...

it happened on a brand new bobbin.

i've done drops up to 120m on bobbins w/o issue...

[hunter]

Hank,
What kind of rope? I've used my Stop on a lot of caving rope and some dynamic rope and never had this issue. Knowing which ones to avoid would be handy.

James Hunter

[hank moon]

Hank,
What kind of rope? I've used my Stop on a lot of caving rope and some dynamic rope and never had this issue.

It was an EZ bend rope that was brand new and had not been soaked prior to use (shoulda mentioned that earlier). Soaking nylon ropes prior to use (especially slinky ones) is a good idea to help prevent sheath slippage.

[Ralph E. Powers]

Hank,
What kind of rope? I've used my Stop on a lot of caving rope and some dynamic rope and never had this issue.

It was an EZ bend rope that was brand new and had not been soaked prior to use (shoulda mentioned that earlier). Soaking nylon ropes prior to use (especially slinky ones) is a good idea to help prevent sheath slippage.

Does "slinky" apply to the Maxi-wear brand of PMI ropes? I've a spool coming my way soon and would like to avoid that slippage problem. Would I need to soak mine as well?
I've experienced a "fast rappel" on a brand new length of PMI-Maxi that hadn't been treated prior to usage. After the first couple of times it was okay. I anticipate this with my spool and realize that it is from the (oils??) on the rope after manufacturing.

Ideas? Thoughts?

[hank moon]

yo ralph

slinky most definitely does not apply to PMI max-wear. however, it is just about the worst choice of rope for use with a bobbin. that stuff is made for racks, man!

[Ralph E. Powers]

yo ralph

slinky most definitely does not apply to PMI max-wear. however, it is just about the worst choice of rope for use with a bobbin. that stuff is made for racks, man!

Nnn now you tell me... :P Well, I bought it because my last bunch wore like iron... hmm wonder if the Pit-rope would be better... mebbe I can change my order?
I want to be able to have a rope that can accomidate every device (as I train many) but want to have that strength of sheath and other positive qualities Maxi-wear provides...

If it's too late... sigh... ah well.

[David_Campen]

hmm wonder if the Pit-rope would be better...

I think it would be the same - IIRC, pit rope is the same as Maxi-wear just without any color in the sheath

[hank moon]

hmm wonder if the Pit-rope would be better...

I think it would be the same - IIRC, pit rope is the same as Maxi-wear just without any color in the sheath

Yep, c'est ca.

[CaveStar]

What is the function of soaking the rope prior to first use? I'm assuming you don't mean that I have to carry the rope into the cave all wet, but rather that if I soak it beforehand and let it dry, something about having been wet will still help hold the sheath where it belongs afterwards. How does this work?

[ian mckenzie]

Presoaking shrinks the sheath onto the core, which reduces slippage when it has dried. We had some big-time problems with 9mm sheath slippage in Peru in 2001, and preshrunk our ropes prior to future expeditions.

[Scott McCrea]

I thought nylon doesn't shrink.

[ian mckenzie]

Good point. My understanding is that it tightens the weave, and doesn't really shrink the actual fibres.

[potholer]

I'd assumed that most people soaked their new ropes before use, to help tighten the sheath onto the core, let the rope shrink to nearer its ultimate length, and get rid of the detergents/lubricants from when the rope was made - a brand-new rope can be horribly soapy and slippy the first time it gets wet.

I tend to repeat cycles of dumping coiled lengths of new rope in a crate of water and then taking it out to drip-dry and changing the water until the water stops looking soapy, or feeling soapy between my fingers.

Some views at:

http://www.zentastic.com/misc/life-on-a-line-part-1.pdf (section 2f onwards)

http://web.ukonline.co.uk/andy.mccarron/cncc/cor.htm (about half-way down the page)

[caverdoc]

When I get a new static rope (except for the few polyester Cancord lengths that I own) I soak it for 24 hours in a large barrel of water (typically a cleaned-out trash can). Periodically agitate the rope in the water to get it thoroughly soaked. Remove and let it drip-dry. If you don't have a trip coming up, once it's dry, toss it into some fresh water and repeat. This shrinks the total length of rope to a "true length" so that 50m rope isn't 2m off the pit floor!
I've read in some European sources that the clubs anchor a spool-type descender and run the wet rope through after cutting a couple inches off the end (without fusing the sheath to core). This "milks" the sheath down the core and off the end. After running the rope through this drill a couple times it is good to go. The only American ropes that I've had trouble with in this regard is some Smith Safety Products (SSP) 10mm from the 90's that I had. Using the anchored descender trick fixed the problem.
Most of my current rope stock is Highline, which is pretty tight. I do own quite a bit of 10mm PMI and haven't had the problems with sheath slippage described. I've also heard of some clubs rotating which end of a rope goes down the pit to prevent the sheath bunching.
Doc K