Rope strength vs. tree strength

[Dadatwins]

Just finished a 2 day class with UAA /MAC ISA on safety and awareness. Nice to see Don Blair give a few talks on safety and rigging. Mr. Blair did make a hard point that I think should be recognized concerning rope strength vs. tree strength. Talked about how years ago when we used 1/2" manilla rope with 4k lb break strength, most climbers picked better anchor points and were very carefull about how big of a piece to cut. Now we have double braided 3/4" bull ropes with 20k lb breaking strength and he is seeing more crotch failures due to new climbers putting too much confidence in the rope and not thinking about the tree strength factor. As he said "The ropes are getting stronger but the trees remain the same" Most old climbers are still cutting the same size logs that they cut when tied with manilla, with today's double braided and tenex. This increases the safety factor of the rope used. Newer climbers who have never dealt with older type ropes tend to push the limit of the rope and forget to factor in the anchor strength. I think its great that newer ropes have made this biz so much easier and given climbers the ability to make larger cuts and get the job done faster and safer, but we must always consider, just because the rope srength moves up, the tree strength usually does not. Think about it and be careful.

 

[vharrison2]

Great post

 

[Stumper]

Actually 1/2 inch Manila was 2450lb tensle rope-give or take two or three hundred depending on manufacturer. When I was a kid the 1/2 inch was the climbing rope. 5/8ths Manila was the light bull rope and we had some 7/8ths braided nylon for the big hairy pieces. I agree with the gist of Blair's point though. Another trhing that I have noticed is that new climbing techniques, great though they are , have driven one of the old rules out of practice. The rule that I grew up on was ALWAYS run your rope around the trunk or the primary branch of the crotch. Throwlining into the top has made for greater efficiency in some cases but a lot of climbers are hanging on secondary branches in marginal crotches that haven't been inspected up close. It is more prudent (and would save some guys a lot of throwing) to throw into a lower/stouter crotch and advance a time or two in the tree.

 

[MasterBlaster]

I love breaking ropes, under the right situation.

 

[Ekka]

What you'll also find is that the force at the lowering point is double plus some for dynamic loading.

So, it would be good to get some failure stats of different dia and types of wood .... compressed upon it's own axis. In other words quantify it's lowering strength.

 

[RedlineIt]

And now we're taking boat winches that can crank 40:1, slapping them on the bottom of the tree, calling it a GRCS and cranking off whacking huge chunks of a tree all at once.

Anyone else get a bit of a sick feeling in their stomach >hoping< their rigging point can stand the forces the winch can exert?

It's a great tool and I'll use it again, but I'll go much smaller pieces than the GRCS can handle in the future. Our tools and techniques are making the trees look so puny.

Time to take a step back.

RedlineIt

............the redline is there for a reason, after all.......

 

[Frans]

And now we're taking boat winches that can crank 40:1, slapping them on the bottom of the tree, calling it a GRCS and cranking off whacking huge chunks of a tree all at once.

Anyone else get a bit of a sick feeling in their stomach >hoping< their rigging point can stand the forces the winch can exert?

It's a great tool and I'll use it again, but I'll go much smaller pieces than the GRCS can handle in the future. Our tools and techniques are making the trees look so puny.

The GRCS has a safe working load of 2500 lbs.
Shock loading can reach this working load limit with very light loads of 200 & 300 lbs.

The GRCS is designed to be able to work in just about any tree removal job. Should the user exceed the working load limits of the rigging or the rigging control device that person, and that person alone (not ANY device or rope), has the sole responsibility for any failures.
Nice try to attempt to blame the rigging or the rigging control devices. Kinda like saying the car is at fault for driving too fast....
I agree that proper training and experiance is essential to do our job safely, but is this not true of just about any trade?
Where you from? drop me a line via PM and i'll send you a video of drop testing the GRCS vrs. the Hobbs w/ a Volvo station wagon.
Frans

 

[Mike Cantolina]

When Blair said 4k breaking strength I'm pretty sure he also said 1" manilla.


Mike

 

[John Paul Sanborn]

Anyone else get a bit of a sick feeling in their stomach >hoping< their rigging point can stand the forces the winch can exert?
...

What Frans said and then some.

I do push the limits of my work, and have on occasion pushed to failure in noncritical situations, just to see what can be done.

To be in a critical situation and having great concern as to what will happen follows a "cut and pray" mentality.

If you "think" it will do what it is supposed to, then are practicing improperly. One does that only when an error will not mean anything big.

When in a critical situation, do only what you know will work.

But then you followed up with saying that is what you will be doing from now on. Just don't be afraid to take a chance in a wide opemn scenario.

 

[fiddlesaw]

come on, people talking about rope strength today?! How big are these pieces that cause the crotch or line to fail? Most of the time I use a crotch on the back side of the trunk, that is gonna increase the strenght quite a bit, don't you think?

 

[Jim1NZ]

It may not necessarily be the size of the wood being lowered, its the dynamic loads which do the damage.

What do you mean, using the back side of the tree?

Crotch strength studies of different species has been carried out, its just a matter of finding the information.

 

[John Paul Sanborn]

How big are these pieces that cause the crotch or line to fail?

Sometimes going big is what it takes to get it done in a day.

With rope failure, it's not just weight and force, but cycles to failure. If you max out a rope on a job then you may want to retire it after that job. I've built rope cost into jobs because I'm figuring in a 4:1 vs 10:1 SWL.

Brudi (did I spell that right Tom?) gave a talk on this last year I think. The 10:1 came up because no one really knows where we can go with this and people tend to over do it and use their ropes till the start to dryrot.

 

[Tom Dunlap]

Erk Brudi...

Since we have very little knowledge about tree strength it's always better to go smaller. The work that Erk has done can be used as a general guideline. He's done more work on whole trees and large parts of trees. Unless we were to pull-test every rigging point we have to rely on experience. The problem with this is that we really don't know what our safety factor is. We might use a limb that would test out at 10:1 and then another limb in the same tree might only be 1:1 and they could look the same.

Looking at trees after storms is a really good way to understand strengths.

 

[Dadatwins]

Unless we were to pull-test every rigging point we have to rely on experience. The problem with this is that we really don't know what our safety factor is.

Think that was Mr. Blair's point, lots of older climbers have broken a few ropes experimenting to see what it will hold and learn from it. Problem with the new stuff, it is so strong that the tree is becoming the test zone.