How rope fails under load

[snowleopard]

Just helped an attempt to move a bogged down truck by towing with a long length of rope. Abandoned the attempt in the end but the modes of failure were interesting.

Knots:

Bowlines held
Double sheet bend: the sheath of one of the ropes started to melt then snapped and the core slid through
Rolling hitch slipped

Rope
Marlowbraid (14mm) snapped over an edge. Later it started to fail along its length with tears in the sheath resulting in hernias where the core protruded.

Dyneema (14mm) survived intact except where the sheath pulled off as described.

 

[ZuidWester]

Most of the failures with climbing ropes result from contact with sharp edges. The sheath is really only there to protect against abrsasion. Still alot of ropes get chucked because the sheath looks abraded. Lots of them end up on my boat. Great for mooring lines as they're springy!

 

[Ships_Cat]

Indeed interesting. Thanks for posting it.

John

 

[Danny_Labrador]

Many years ago I used to muck about with Land Rovers off road and all that. We always has a special “tow” rope with us 30 ft nylon 3 inch diameter, shackles each end. To get stuck vehicle out of mud attach and accelerate away - rope was designed to stretch (a lot) - eventually it reached its limit but the combines elastic force of the rope starting to try to retract and the vehicle still accelerating away would un plug anything – still have it, very useful.
Only downside was that you had to watch out for the recovered vehicle slamming into the rear of the tow vehicle at high speed !

 

[peteandthira]

Isn't "sheath" a naughty word?

 

[jimi]

Once towed a tree trunk out with an old climbing rope .. fortunately it was a company car!!

 

[mirabriani]

Me too
The All Wheel Drive Club occasionally cooperated with the Trail Riders Fellowship. Was it called a snatch rope?
Anyway on one situation the rope broke, sprang back and smashed a headlamp. Nearly took some ones head off too!

Moral, keep clear of tow ropes on board.

Safe regards Briani

 

[snowleopard]

I insisted everyone was kept well clear as the load came on. Each time something broke the ropes shot back at huge speed but, interestingly, they didn't go more than about 3 ft from the line of pull.