8 tonne rope failure, shock loading

[randyg]

I have run the whole thing through a hundred times, and aside from coming up with a way of pretensioning a 4 inch line set horizontally 50 feet away or just having a bigger line, I dont think I could have done much different aside from aiming the tree more at the house, but even that make me worry about how things could have been much, much, much worse.

I dont think Im being to pedantic. I take my very clean record for breakage very seriously. Big tree, bad ground, target rich environment with a tight timeframe and limited options. I am confident in my ability and track record but I am simply not happy with how it went, do I just need to harden up?

Had you pretensioned that line, the tree would have started over and shortly after the line would have halted the felling process completely. Been there, done that, not a good feeling having that tiger by the tail. Fortunately for me, I was tied off to truck and able to release the brake and follow down, with 26,000 lbs plus of truck skidding near the end, but nobody got hurt. Pucker factor was at an all time high. I since learned how to "predict" that scenario and adjust/eliminate altogether.

For me, I try and picture a door with two hinges. One is the hinge on the tree being felled, and the other the anchor point of the side loaded line (the stump in your case). One principal to keep in mind is the "hinge pins" must be in line. If you hung a door and the hinge pins were not in line, as you closed the door they would bind and something would have to break to get the door shut.

SIDEBAR: If you had a 20" diameter at the stump tree and after making the face cut and kicking out the "pie" you rolled a 20" long piece of 1" pipe all the way in to the apex of the face cut, and got down on one knee and eyeballed through that pipe, you SHOULD see the anchor point. If you can not, that line will either go slack or go tight as the tree starts over. No, I don't carry around a pipe, but you bet your boots I get down and eyeball along the apex to look for proximity of the anchor point. Start with a very shallow notch and adjust till it is sighted in, then make it deep as you want and re-check alignment.

Timber, using that stump like you did, and adjusting the hinge accordingly, I think the tree would have fallen way to close to the house. I'm not trying to explain how you should have done it differently, but hoping to explain WHY the rope broke. The desire to be more accrurate predictors sets us apart from those "cut and see" types.

What I WOULD have done differently if time allowed would take more limbs off the downhill side and leave them all on the uphill to counter the lean.

 

[TimberMcPherson]

Trucks always make me nervous as anchors but we dont always have much choice. Your right about lining up the hinges between scarf and arc of travel, the direction was fine as you can tell by where the tree ended up landing, I just didnt send the tree towards the house which would have got the line tight. Line got shock loaded instead of loaded by tree heading towards house gently, it snatched when the tree was about 45 degrees over, thats what broke it

If it was tensioned it wouldnt have stopped the process, and if I was able to pretension the big line I would have scarfed the tree differently, the idea of doing a collapsing scarf towards the house was to tension the line so it could swing the tree sideways along with winch help.
the tirfir had plenty of pull and the way the big line would have just guided it sideways, restricting its felling path in an arc.

A great plan if only I had the faith to aim the tree at the house! (well the best plan 4 arbs could come up with at the time)

 

[knudeNoggin]

Instead of a huge standard fiber like look into the exotic fiber, super low stretch, high tensile stuff..
You will have a smaller diameter line for the SWL and less stretch to take up on pretensioning.

And much less tolerance for dynamic/shock loading. (The rapid loading that
I've seen stated for tug lines of HMPE is a far cry from "shock" as seen here.)

Yeah, the line on top with the splice is [it]

Oh, hmmm, not the more monstrous lines around the saw, also with splices,
but 8-strand not 12/24?!
We haven't heard what the composition of the monster line was, but from
the photo & color, I'm guessing it's the increasingly popular CoExtruded PP/PE
material (often erroneously called "copolymer" (Technora is a copolymer,
in a technical sense, but not the coextruded stuff)). That's not so good for
absorbing shocks, in material or structure. (A light blue hue is common,
though there are some other colors.)

Btw, where did the break occur in the line--at a splice, or elsewhere
(since you said it kinda caressed the house, I guess it broke towards
the anchor end and was flung over ... )?

The bigger lines of your picture might be "polyDac" combo-fibre lines
(where polyester is combined w/PP or increasing CoEx, to bring surface
qualities vs. UV & abrasion of PES with lightness of olefins). And the
8-strand I think has more inherent load absorption.

Could a good big laid nylon bridle have given you the cushion necessary,
I wonder? --it's the sort of thing done in some heavy towing, at least.

-------

I did get a knot in it that required careful use of a sledgehammer ...

Which knot?
(In mooring lines of trawlers I've seen lots of bowlines that have capsized
into Pile Hitches on a dog-legged standing part! But a simple extended
tucking of the end could prevent this.)

*kN*

 

[knudeNoggin]

Hmmm, still curious, about which rope & knot.

*kN*

 

[TimberMcPherson]

Sorry missed your post!

Breakage occured about 15mm from the end splice which was attached to the falling tree, I regularly check my ropes and although this rope was far from being perfect, there were no obvious areas of weakness.

The knot was a simple marlin spike. My climber had tied it to secure the line a hitching pin we put on the end of a diggers arm to pull over some pines, pin came out easy, knot required some work. Really hard to put knots in such a long and heavy line. We kept it in a wool sack and used it from there.

Im not sure what you mean by a nylon bridle, is it like the rubber suspension you find on mooring lines?