Caving Rope Used to Pull Stuck Vehicle

[Scott McCrea]

We used one of my ropes to pull a SUV out of the snow in WV this weekend. Conventional wisdom says to retire the rope, which I will. But, does any one know of such a rope being pull-tested? Was strength seriously compromised?

[jharman2]

I've done the same thing with a caving rope. I immediately retired it to use as a tow rope. Said rope currently resides in my Jeep and pulled out several more stuck vehicles last year.

I'd be REALLY interested to see there is any decrease in strength.

I'd even be willing to donate my tow rope for testing!

[Carl Amundson]

I would retire it.
The problem as I see it is not the forces applied to the rope as a result of the towing, but possible exposure of the rope to oil, grease and road salts.

[chh]

Casual exposure to gas and oil will not really damage a rope. I'm not sure about salt
Scott, American Cable and Rigging on 280 will pull test a rope for you for a nominal fee. 15 bucks or so? Their rig is probably not big enough to pull test your entire rope, but maybe the section that saw the most abuse in the tow. Also, with breaking strength you'd also have to consider the age and previous wear and tear the rope may have suffered in the outcome.

So, approx. weight of a 4WD SUV: 4000# Approx breaking strength of new pit rope 6500# Could be that an older rope would break at 4000 anyway if you truly did weight it that much. But to give someone a tow you don't always load the rope anywhere near the weight of the vehicle, though concievably you could load it with even MORE than the vehicle weighs, depeinding on the situation.

So lets assume a 5000# breaking strength on an old rope. Working loads differ between ropes used for rigging and those used for climbing, but lets assume a 20% "safe" working load. That's 1000 pounds. Do you think you loaded it with more than 1000 pounds? Or thinking about it in another way, let's say an average single person with good footing can put 100 pounds of force on a pull rope ala tug-of-war style. Do you think you could have achieved the same "tow" with ten people?

Lot of assumptions in there, but it's fun to think about. If the rope was in good condition before the tow, I think I might just lop off the end of the rope used in the tow and salvage the remaining rope if there's enough there to use for something.

I just use 2 inch tubular webbing for my tow strap. Slightly cheaper per foot than than the straps you buy in the store, readily available in any length, and they usually take up less space than traditional tow straps. Quit using your caving ropes!

[MUD]

Quit using your caving ropes!

...and learn how to drive!

[Scott]

I have had to do that in Wv, Pa and once in Va. Rope got retired and has been used to haul tools/dirt out of pits we were digging. I rigged one from a 12 ft tall branch and played on it with my vertical gear and didnt notice any change, but that was only 12 feet and i wouldnt do it in a cave.

interesting to see if you can get it tested and see the results.


Scott

[Stridergdm]

And if you do insist on getting stuck in a snowbank, hope that these guys don't offer to pull you out.

(funny thing is same day I first saw that, about 5 years ago, on the way home, I came across a kid who had skidded off the road. And yes, used my trusty first piece, of long retired piece of webbing to get him back on the road.)

Word of advice too.... static rope works far better than dynamic rope.

But I still prefer webbing. Double it over a few times and you've got plenty of strength.

[NZcaver]

Yeah, I've retired caving rope to use for pulling vehicles too.

Be interesting to see what it breaks at, especially if there's a sample of the same stuff that wasn't used as a tow rope. My biggest concern would be the effect of using a static rope as a dynamic snatch strap. This often happens when getting a vehicle unstuck, and the towing vehicle starts with a slack line and then guns the engine to "snatch" the other vehicle out. With the right equipment this can be very effective, but there's a high peak force involved. Maybe not so good for a caving rope. Plus you'll *never* get the knots undone again.

[davantalus]

Same thing happened to me... Slightly different circumstances. My buddy ended up with a brand new beautiful 7/16" tow-rope.

viewtopic.php?f=5&t=9842

[knudeNoggin]

We used one of my ropes to pull a SUV out of the snow in WV this weekend.
Conventional wisdom says to retire the rope, which I will. ... Was strength seriously compromised?

You've left out information that would help make the decision
--and "conventional wisdom" looks damn shallow if it doesn't
seek such help! I'll repeat what I wrote/asked (unanswered)
in the thread referred to above.

How did you use the rope, exactly? I.e., how was it configured,
was it knotted, and so on. How does it look, afterwards, and how
does it feel? Is it the same length (and not now longer & thinner)?
I imagine that the pulling was done with care, slow-delivery,
in concern for the rope and vehicles. Could say four big guys
have pushed that vehicle out? That SUV was helping itself move,
wasn't it?

(My guess is that your rope is fine. And this is a caving not rockclimbing
forum, so we're not concerned with great loss of dynamic capability.)

The How-much-is-your-life-worth-? doubters could put that question
to anything: at some point, one needs to be able to evaluate the
circumstance beyond conjecture. The breaking strength of that
rope might be nearly adequate to hoist the vehicle, and
merely pulling it --"mere", at least, in some cases-- will take far
less load. Nylon fibres can endure about 70% of their maximum
load w/o sustained damage, I've been told [long ago, by a tech
chief at Plymouth Cordage (Goldline, remember?)]. And if you doubled
the rope (perhaps making a big loop/sling), you are halving the
force per strand. If the rope looks fine and knots weren't welded,
you're probably fine.

(As for petroleum products, well, petrol per se isn't an issue,
though for some time it was a rumored issue --rumors out race
research/facts, often-- ; additives in petrol might be.)

*kN*

[knudeNoggin]

We're still lacking the obvious information to complete this question:

How was the rope for the tows rigged?

davantalus wrote (in an earlier thread): "my 70 foot length of ~13mm static rope was used to pull my buddy's Acura MDX out of a small lake in the road"
and implied that it was end-2-end, single strand (in being just long enough to keep tower clear of the "small lake").

Scott has not described his tow rigging.

NZCaver suggested, on really hard (& thus potentially damaging) tows,
"you'll *never* get the knots undone again" --but did you guys knot,
and how, and how were the knots afterwards? These can be indicators
to address the question, which I'm surprised are not yet brought forward.

So, how was the tow rigged?

*knudeNoggin*

[Scott McCrea]

The rope was tied on both ends with bowlines--so we could easily untie them. It was steady pulled horizontally with no bounce. The 50' rope stretched a lot--probably ~10'. There is no visible damage and I don't feel and defects in the rope.

[knudeNoggin]

The rope was tied on both ends with bowlines--so we could easily untie them.
It was steady pulled horizontally with no bounce.
The 50' rope stretched a lot--probably ~10'.
There is no visible damage and
I don't feel any defects in the rope.

Thanks for the information. This points to what I think
is not severe use and an okay rope; but we have to note
that there's a lot of *guesstimation* in my back-of-napkin
reasoning.

At 50' with **about** 10' stretch --and the estimate probably
came from noting the length of the tow vehicle, etc.--,
figuring maybe 6' consumed by the two bowlines,
you have then 44' single strand enduring the load and
yielding most of the stretch,
which thus figures to be 20-23%ish.
A cursory Googling for info on ropes of this sort showed one
elongation-at-rupture figure of 30%. Working with these
figures and the particular rope maker could gain better
assessment (though they might have a CYA stance in any
offered advice). (A rope-engineer I pinged re this didn't
think that there'd be any or much damage at 20%, again,
in ballpark figuring.)

Another thing to consider is if the rope seems to have
taken a permanent stretch; I think that with some time
to relax that it will recover much stretch.

*kN*