Snubbers and climbing rope

[thinwater]

Originally Posted by nhschneider

We use a bridle made of 18mm 3-strand nylon with stainless steel thimbles spliced into one end and eye splices into the other end. I recently replaced the chafe guard, using fire hose material which I stitched into place with a heavy whipping twine. We were anchored off of the southern Baja California coast in some northerly winds of about 25 knots and the rope bridle stretched so much that stitching that held the chafe gear in place snapped on each side of the bridle (the chafe guard remains in place as it’s secured still on one end). The bridle is almost 4 years old and has seen hundreds of days in use.

Fair winds and calm seas.

Yes, chafe gear must float. In fact, it is better to anchor it to the chock and not attach it to the rope at all.

[LongRange]

If very high snatch loads are anticipated, never use a prusik or rolling hitch or anything of the sort on the standing (load bearing) part of a kernmatle rope, including a climbing rope.

In the vast majority of such ropes the core floats inside the woven sheath. A knot like a prusik engages the sheath, with comparatively little engagement of the core. The sheath can thus get stripped by very high impulse forces, which absorbs a a bit of force but also completely destroys that section of the rope, with a greatly increased chance of total failure during the next massive tug.

Climbers use prusik knots to climb ropes, in lieu of a mechanical ascender, not to take the force of a fall.

A small percentage of climbing ropes are of a very modern "unicore" construction, where the core and sheath are mechanically bound to each other (by glue or weave). I expect that stripping the sheath with an ascender - or a prusik knot - is less likely with a unicore rope, though the jury is still out on whether unicore is a good thing overall.

[pmagistro]

Originally Posted by LongRange

If very high snatch loads are anticipated, never use a prusik or rolling hitch or anything of the sort on the standing (load bearing) part of a kernmatle rope, including a climbing rope.

In the vast majority of such ropes the core floats inside the woven sheath. A knot like a prusik engages the sheath, with comparatively little engagement of the core. The sheath can thus get stripped by very high impulse forces, which absorbs a a bit of force but also completely destroys that section of the rope, with a greatly increased chance of total failure during the next massive tug.

Climbers use prusik knots to climb ropes, in lieu of a mechanical ascender, not to take the force of a fall.

A small percentage of climbing ropes are of a very modern "unicore" construction, where the core and sheath are mechanically bound to each other (by glue or weave). I expect that stripping the sheath with an ascender - or a prusik knot - is less likely with a unicore rope, though the jury is still out on whether unicore is a good thing overall.

Actually we use three-wrap prussiks as a standard in rope rescue. Two 3-wrap prussiks has been a standard belay in rescue for years. Some teams are using different systems now but the data stands.

The exact forces change based on materials, but in general a prussik provides a force-limitation on the system, slipping around 6kn then regripping and distributing peak forces over a longer time period. This is an important safety feature to a system designed for live loads.

The only issue you may run into is that with repeated loads or very significant loads beyond the slip/regripping threshold for a prussik hitch, the prussik and/or host rope may glaze and become damaged or fail. Anytime a well dressed three wrap prussik slips, the involved components should be a) replaced and b) analyzed to determine what cause the excessive peak loading.

[thinwater]

It's important to remember that a snubber or rode system that is seeing loads beyond the SWL on the rope (ABYC H-40 Table AP-1) is not going to last long In general, this means at least 35 feet of nylon, although details vary. Just as high fall factors increase the risk for climbing ropes, short snubbers and rodes increase risk for anchoring an mooring.

[LongRange]

Originally Posted by pmagistro

Actually we use three-wrap prussiks as a standard in rope rescue. Two 3-wrap prussiks has been a standard belay in rescue for years. Some teams are using different systems now but the data stands.

The exact forces change based on materials, but in general a prussik provides a force-limitation on the system, slipping around 6kn then regripping and distributing peak forces over a longer time period. This is an important safety feature to a system designed for live loads.

The only issue you may run into is that with repeated loads or very significant loads beyond the slip/regripping threshold for a prussik hitch, the prussik and/or host rope may glaze and become damaged or fail. Anytime a well dressed three wrap prussik slips, the involved components should be a) replaced and b) analyzed to determine what cause the excessive peak loading.

Thanks for the info. I would never use a prusik in any situation where I am anticipating anything beyond a factor 0.1 fall. The "sliding dissipates force" thing is all very well, until an abraded sheath causes so much friction that the prusik rope simply melts, or the prusik manages to grip and strip the sheath clean off. It is only a question of which of the two ropes is getting damaged. Unfortunately for me, I have seen accidents caused by that practice, including a fatality.

There is no need for it either. Something as ubiquitous and versatile as a grigri provides far greater safety. (Not recommended for marine use, especially not for snubbers )

[pmagistro]

Originally Posted by LongRange

Thanks for the info. I would never use a prusik in any situation where I am anticipating anything beyond a factor 0.1 fall. The "sliding dissipates force" thing is all very well, until an abraded sheath causes so much friction that the prusik rope simply melts, or the prusik manages to grip and strip the sheath clean off. It is only a question of which of the two ropes is getting damaged. Unfortunately for me, I have seen accidents caused by that practice, including a fatality.

There is no need for it either. Something as ubiquitous and versatile as a grigri provides far greater safety. (Not recommended for marine use, especially not for snubbers )

While it's well beyond the scope of this discussion, the testing bears out an acceptable level of safety at a fall factor of .33, which is an accepted "worst case" in rescue and thus the basis for much detailed testing. My training allows us even to lead on static ropes, as long as we mitigate fall factors to .33 or less.

As it relates to sailboats and snubbers, that is the reason I state that either dynamic or static climbing ropes, in my opinion, would be acceptable and offer benefits.

[LongRange]

Originally Posted by pmagistro

While it's well beyond the scope of this discussion, the testing bears out an acceptable level of safety at a fall factor of .33, which is an accepted "worst case" in rescue and thus the basis for much detailed testing. My training allows us even to lead on static ropes, as long as we mitigate fall factors to .33 or less.

I tend to fall lots, so for me that is not an option

Originally Posted by pmagistro

As it relates to sailboats and snubbers, that is the reason I state that either dynamic or static climbing ropes, in my opinion, would be acceptable and offer benefits.

What would be the benefit of swapping out a stretchy nylon 3-strand snubber, which costs on the order of $1/m, for a static climbing rope which is designed for low stretch at a cost of $4/m+?

[pmagistro]

Originally Posted by LongRange

What would be the benefit of swapping out a stretchy nylon 3-strand snubber, which costs on the order of $1/m, for a static climbing rope which is designed for low stretch at a cost of $4/m+?

My point was more that either dynamic or static retired climbing rope would likely provide similar benefits and durability as three strand, and that it may be possible to source large amounts of either at little or no cost from climbers who hate to throw things in the garbage.

[LongRange]

Originally Posted by pmagistro

My point was more that either dynamic or static retired climbing rope would likely provide similar benefits and durability as three strand, and that it may be possible to source large amounts of either at little or no cost from climbers who hate to throw things in the garbage.

Whether or not dynamic climbing rope is appropriate for replacing nylon 3-strand as a snubber is the topic of most of this thread, and it is probably fair to say that opinion is divided.

Static climbing rope is a completely different story. It is purposefully engineered to reduce stretch, which makes it a poor choice for snubbers. Halyards, maybe, if it's going to waste

[sailingharry]

Originally Posted by LongRange

Whether or not dynamic climbing rope is appropriate for replacing nylon 3-strand as a snubber is the topic of most of this thread, and it is probably fair to say that opinion is divided.

Static climbing rope is a completely different story. It is purposefully engineered to reduce stretch, which makes it a poor choice for snubbers. Halyards, maybe, if it's going to waste

According to the data provided by pmagistro, a static rope elongates 2-4% with "typical" loads. If you assume "typical" is a 200 pound person, then that would extrapolate to 7-14% at 700 pounds. 700 pounds is about 15% of the breaking strength of a 3/8 (9.5mm or so) double braid nylon line. NE Ropes 3/8 double braid has a breaking strength of 4800 pounds, and a stretch of 6.5% at 15% (or 700 pounds). Sounds like static line is at least comparable to the ubiquitous double braid nylon dock line (agreed, double braid nylon is the worst dock line in common marine use -- 3 strand is better, and 8 plait is the best).


If I could source good condition static line at less than 50% the cost of new double braid, it sounds like it would be an improvement over double braid -- and if I could source it at 25% the cost of 3-strand, I might well consider it.


Fully agree that dynamic rope is a better choice.


Harry

[LongRange]

Originally Posted by sailingharry

According to the data provided by pmagistro, a static rope elongates 2-4% with "typical" loads. If you assume "typical" is a 200 pound person, ...

I do not think those numbers are congruent. A static rope will typically stretch only half a metre or so when top-roping over the entire 50m length. That's with a crab up top, which provides extra friction, thus leading to unequal loading on the two halves. Say 70-90cm with a rescue pulley, instead of the crab. That low stretch is why static ropes are sometimes used for top-roped belay during dozens or even hundreds of attempts at the same crux section.

Otherwise, static ropes are typically used for gear hauling, where weights are far in excess of 80kg, so I would guess pmagistro's "2-4%" stretch stats refer to hauling loads in excess of 100kg.

A rope that stretched that much uder the weight of a single climber would fall into the "semi-static" nomenclature, as used by Beal and Edelrid. Those are ropes that could potentially be used for lead-climbing, in an emergency, as long as the fall factors remained low. Since pmagistro mentioned "training" for lead-climbing on static ropes, perhaps they tend to use semi-static ropes in his neck of the woods.

Myself, other than clenching even harder than usual, I cannot think of what training I could apply to mitigate the awesome forces generated by a lead fall on a static rope. "Pop, pop, pop, goes the pro as you drop."

[pmagistro]

Originally Posted by LongRange

I do not think those numbers are congruent. A static rope will typically stretch only half a metre or so when top-roping over the entire 50m length. That's with a crab up top, which provides extra friction, thus leading to unequal loading on the two halves. Say 70-90cm with a rescue pulley, instead of the crab. That low stretch is why static ropes are sometimes used for top-roped belay during dozens or even hundreds of attempts at the same crux section.

Otherwise, static ropes are typically used for gear hauling, where weights are far in excess of 80kg, so I would guess pmagistro's "2-4%" stretch stats refer to hauling loads in excess of 100kg.

A rope that stretched that much uder the weight of a single climber would fall into the "semi-static" nomenclature, as used by Beal and Edelrid. Those are ropes that could potentially be used for lead-climbing, in an emergency, as long as the fall factors remained low. Since pmagistro mentioned "training" for lead-climbing on static ropes, perhaps they tend to use semi-static ropes in his neck of the woods.

Myself, other than clenching even harder than usual, I cannot think of what training I could apply to mitigate the awesome forces generated by a lead fall on a static rope. "Pop, pop, pop, goes the pro as you drop."

We've digressed pretty far from the sailing application, but here's a bit more data and info, along with some thoughts:

I use Sterling HTP static for rescue work, 10mm. 1.4% elongation at 300lbs, presumably more at higher loads but I don't have that data at my fingertips. I am perfectly comfortable leading on that rope, providing I can manage the fall factor to .33 or less (lowering the belayer, placing lots of protection especially lower on the route). It isn't standard practice per se but acceptable, as the forces an 80kg climber would create falling on that rope with a .33 or less fall factor are within the 6kn limit we want for our bodies (and the excellent protection I place when doing so). As it related to snubbers, the extrapolation is that even a super low stretch rescue rope provides significant reductions in impact forces with enough rope in service. Hence my earlier assessment that I believe that a long snubber of either dynamic or low-elongation rope would be acceptable.

The "awesome forces" LongRange refers to are certainly possible in high fall factor situations, but the testing I have seen bears out that if you keep the fall factor low, the forces remain comfortably low as well.

If you look at more common nylon "statics" like the PMI EZ Bend that is sold at REI stores everywhere, elongation specs are 1.6% at 300 lbf | 3.0% at 600 lbf | 5.8% at 1000 lbf. More generous for sure than the polyester statics that my training/testing/knowledge deem adequate.

So I'll stand by my statement that, -in my opinion-, a retired climbing rope in reasonable shape (such as a good section cut from a longer coreshot rope) should serve fine for the purpose of a snubber. I can't say it would be better or worse than 3 strand, except that retired climbing rope is an inexpensive or free resource that I hate to see go to waste.

[LongRange]

Originally Posted by pmagistro

We've digressed pretty far from the sailing application, but here's a bit more data and info, along with some thoughts:

I use Sterling HTP static for rescue work, 10mm. 1.4% elongation at 300lbs, presumably more at higher loads but I don't have that data at my fingertips.

Yes, that would be ~0.82% elongation at 800N, which is half a metre of stretch when top-roping an entire 50m rope, like I mentioned earlier. That is indeed a true "static" rope. Other than hauling gear, it's only legit use in climbing is to prevent decking-out when top-roping and the crux is right near the ground.

Originally Posted by pmagistro

I am perfectly comfortable leading on that rope, providing I can manage the fall factor to .33 or less (lowering the belayer, placing lots of protection especially lower on the route). It isn't standard practice per se but acceptable, as the forces an 80kg climber would create falling on that rope with a .33 or less fall factor are within the 6kn limit we want for our bodies (and the excellent protection I place when doing so).

Lead climbing on a static rope is most certainly not acceptable. Let's just make that very clear for anybody who might be reading this, on a boat forum(!), in years to come, unsure as to whether to grab that halyard and go lead climbing.

A F=0.33 fall on proper dynamic climbing rope will typically generate forces of 3kN on the climber. Other than being exciting, like almost every lead fall, the forces involved would be mild and bearable.

The maths is very complex, but with the static rope you are using, a F=0.33 fall would subject the climber to around 8kN to 9kN, ish, and the top piece of pro to somewhere around 12kN to 13kN. It will not kill, but it will ruin the climber's day, and quite possibly put them out of action for a while. Mediocre pro will fail.

By my back-of-the-envelope calculations, that rope of yours will break bones at around F=0.8, at which point the climber experiences 12kN and the top pro sees 19kN or so. Even drilled and glued ringbolts might fail at that threshold, especially in soft sandstone.

That is why rope companies go out of their way to differentiate dynamic and static ropes by colour and markings, and why in some circles it is common for climbers to give dynamic ropes female names, and static ropes male names. The consequences of accidentally leading on a static rope can be lethal, and barring a life-and-death emergency there is absolutely no need to do something so inherently dangerous.

It used to be done all the time, back in the days of hemp and sisal ropes, before the plastics revolution of the 1950s and 1960s. Back then climbers simply did not take risks that might result in a fall, because falling was often lethal.

The (forced) historical use of static ropes is also one of the main reasons why anything beyond 5.10d was once considered spectacular, while nowadays that grade is practically the entry point into climbing.

Originally Posted by pmagistro

As it related to snubbers, the extrapolation is that even a super low stretch rescue rope provides significant reductions in impact forces with enough rope in service. Hence my earlier assessment that I believe that a long snubber of either dynamic or low-elongation rope would be acceptable.

So I'll stand by my statement that, -in my opinion-, a retired climbing rope in reasonable shape (such as a good section cut from a longer coreshot rope) should serve fine for the purpose of a snubber. I can't say it would be better or worse than 3 strand, except that retired climbing rope is an inexpensive or free resource that I hate to see go to waste.

A static climbing rope is cetainly worse than bog-standard 3-strand, because it simply does not stretch anywhere near as much. Better than no snubber at all, I suppose.

[LongRange]

This diagram is slightly more pessimistic, indicating that 12 kN is reached by 10mm static rope at F=0.7, or perhaps slightly earlier by 11mm rope:



Personally, I'd rather go lead climbing on my 3-strand snubber

(Also totally )

[LongRange]

Originally Posted by LongRange

Better than no snubber at all, I suppose.

I take that back. The weight of static rope is measured in grams per metre, whereas the weight of chain is kilograms per metre.

The shock-dampening effects of chain catenary, debatable though they may be, are thus lost by the use of a static rope to bridge that bit of chain.

It makes static rope possibly the very worst kind of snubber, worse maybe than all-chain on its own, and surpassed in its inappropriateness for this purpose only by spectra, dyneema, and kevlar.