Rope abrasion

[potholer]

A friend of mine has all his ropes with a permanent double-fishermans in one end, held tight by an interwoven cable tie, which is always the bottom end, so if he is caving on his own rope, and the knot isn't at the top, it must be at the bottom even if it's buried in the bag.

The disadvantage here is that the rope will abrade at almost twice the usual rate, because the same end of the rope is always on top.

Could you elaborate on that?
Are you saying abrasion is some directional effect, or making a reference to rigging techniques where rope wear at the top end is a probability, or something else?

[ek]

I doubt there are any directional effects of any kind with modern kernmantle rope.

What I mean is that, if you want to lengthen the time it will take to have to cut off pieces of damaged rope, you can do that by about a factor of two by using a different end as the top end every other time you cave with the rope. The top is most subject to abrasion in almost all circumstances, at least in American style rigging where it is standard to have the rope run directly over an edge (albeit padded...sometimes).

But even in European style rigging, the rope is most likely to rub against the wall where it is clipped to bolts in the wall, right?

[potholer]

But even in European style rigging, the rope is most likely to rub against the wall where it is clipped to bolts in the wall, right?

I'd guess that the likeliest rope-wear situations in European rigging tend to be situations such as significant rubpoints either near pitch-heads (rubbing over convex ledge-edge) or mid-pitch (both cases usually followed very quickly by a rebelay) or glancing contact with a wall, often some way down a pitch, for which there are various causes..
Pitch-head contacts tend to be obvious and short-distance, and even where unavoidable, are largely situations where rope rubbing can be greatly minimised by careful use of the rope, such as climbing gently where the rope rubs over a convex ledge-edge, and don't tend to be situations where wear is noticeable.

However, even if temporary short-distance rubpoints were the main cause of rope wear, and such situations were much more likely just below pitch-heads, in practice, pitch-heads are still often some way from the top end of a rope due to the consumption of rope by traverse lines, and/or the use of a long rope for multiple pitches, so such wear would be spread out over a significant fraction of the rope.
It may well be that there would be very little wear in the bottom 5-10m of a rope always used one way round, but it could easily be the case that there's very little wear in the top 5-10m if that typically ends up being used for little-loaded traverse lines.

In practice, in UK SRT, significant rope wear often seems to be more of an acute problem due to specific instances of mis-rigging (or ropes getting caught behind flakes, etc), rather than a chronic situation due to cumulative wear.
If forced to guess, and thinking of the places I've ended up cutting ropes due to acute wear, or noticed patches of wear when handling ropes, I'd plump for the middle third of a rope maybe being the likeliest third to have a wear situation in.

[ek]

And yet, the likelihood of the amount of rope used for two traverse lines being the same is not so low.

Especially if they are really the same traverse line, as in a cave one visits frequently.

[potholer]

Obviously, if a rope is used over and over in the same cave and that cave has a significant close-to-start rubpoint, then wear will be concentrated, but for me (and my friend with the fixed knots), the only things we might do repeatedly tend to be rope-training trips, which also tend not to have significant rubpoints at all, assuming they are well rigged.

Thinking about it, I can think of a few potholes with unavoidable rubs near a pitchhead, but they stick in my memory as much from their rarity as from anything else, and they are largely rubs on smooth rock, or short rubs close to a rebelay where good ropeclimbing can largely prevent abrasion.

Clearly, the situation may well be different when using non-European SRT, but for me, I doubt that there's enough top-end-specific wear to result in using a rope always the same way round causing the rope to wear out any faster.

Even if wear concentration was a possible problem, for my friend with his permament endknot approach, it'd be simple to just switch ends every year or two, or to switch ends if/when the top end started to show signs of extra wear

[Tubo Longo]

ek wrote: But even in European style rigging, the rope is most likely to rub against the wall where it is clipped to bolts in the wall, right?

Well, the point in setting a rebelay is to avoid that the rope rub the wall.
More: if this happens right above the rebelay isn't much of a fuss at all 'cause basically such rubbing never occurs with a loaded rope (so that the rope may ends up with wear and/or damage). Of course, for the ery same reason, the rope MUST never rub the wall below the rebelay, expecially RIGHT below.

What indeed at time happens is what Potholer already described, exp. about convex ledge-edge: in such a situation while rappelling the caver (and the rope) may be at a safe distance from the wall while climbing the rope tend to rub the wall over a definite section. Not always is practical to set a rebelay and/or a re-directional in such situations: so some care has to be practiced while climbing to the point of rub.

Anyway, at the rebelay the rope should not at all rub the wall: if it happens, the rebealy has not been properly placed and/or set (at time just adding a biner or a sling to the bolt is enough to properly position the rope away from any point of contact).

[hank moon]

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[NZcaver]

As Hank so perceptively noticed, this line of discussion (which was in the Loading a Stop in a "C" thread) started drifting off topic. So now it has it's very own thread. Enjoy.