question about shock loading a rope and blocking

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still scares me. how do you know if your not exceeding the limit on that rope with a skid steer? theres just no way to tell. if that rope snapped it could break a window or worse.
 
Re: question about shock loading a rope and block

funny thing you mention a window.. I did break a storm window on that job.. just unclipped my lanyard and dropped it.. as the clip swung around the tree, it hit an old storm window just wrong.. cost me $20.. freak thing.. you just never know.. lesson learned..

And to answer your question.....
firstly the rope doesn't have to be stronger than the skid steer in that citiation.. it just has to be stronger than the hinge.. (did you notice the holding wood on that stump?)

Secondly... THAT skid steer (on grass) cannot break a rope. Doesn't matter how you tie it..

Thirdly.. I used a double bowline.. good habit!

{I changed the title of the thread after the spam attack midline...TD}
 
Re: question about shock loading a rope and block

I really dont have a problem with the stick dropping my bigger question is the dropping of the top. The back-cut seems way low from the notch. Box or no box this is not that involved that something has to be so radically changed. Small shallow notch with a conventional back-cut would have worked just fine. The pull with the skid steer did all the work. That fancy cut was irrelevant.
 
Re: question about shock loading a rope and block

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I really dont have a problem with the stick dropping my bigger question is the dropping of the top. The back-cut seems way low from the notch. Box or no box this is not that involved that something has to be so radically changed. Small shallow notch with a conventional back-cut would have worked just fine. The pull with the skid steer did all the work. That fancy cut was irrelevant.

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You are coming in a little late on that discussion and are further derailing this thread..
That said, I hit metal on the backcut and was trying to drop the level of the cut down below any potential for the metal. Figured it was some kind of light hanger..
 
Re: question about shock loading a rope and block

Yes I am coming in late, but had a question and frankly didn't want to read through all the fluff to get the answer. Thanks for the answer.
 
Re: question about shock loading a rope and block

Cuttenwolf, you generally don't like confrontation, so don't bother responding to Daniel. Unless you need someone to vent on, then he is your man.
 
Re: question about shock loading a rope and block

heres a new subject with shock loading. so we know there is a way to measure shock loading and stretch values with ropes but is there a way to figure out how much load is put on the slings? what if your using a 5/8 12 strand to block light loads and a super static rope like amsteel for slings. as far as i know your sling should break at a higher value then your rope so what im getting at is if 12 strands stretch more absorbing the shock load is it necessary to have a higher value sling? you would think youd be able to get away with using a 1/2 sling(10,000lbs) with a 5/8 12 strand(10,000).
 
Re: question about shock loading a rope and block

You've got roughly double the force on the block sling as the rope, as you have two legs of rope pulling on your block/ sling.
 
Re: question about shock loading a rope and block

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stretch in the sling has little effect becuase there not much line there to stretch..

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Every little bits helps. Stretch in a block sling is beneficial to the climber.
 
Re: question about shock loading a rope and block

i actually have a friend making me a 14' 3/4 dynasorb sling for me Norm.
cool.gif
 
Re: question about shock loading a rope and block

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stretch in the sling has little effect becuase there not much line there to stretch..

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Every little bits helps. Stretch in a block sling is beneficial to the climber.

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Is there any science to support statement Norm?

Extra stretch in the sling creates (2x the stretch) movement in the piece which might even result in more force, dependng on the other factors...

When the rigging software came out they showed that leaving even a little play in the marl and running bowline would increase the force..

Keeping blocks tied up tight!.. as close to the cut as possible with very little wiggle room is the way to go...
 
Re: question about shock loading a rope and block

Thanks X. That's what I always do. I usually finish off a Cow Hitch by twisting the block with my left hand while pulling the working end of the sling. It tends to cinch it up nicely.
 
Re: question about shock loading a rope and block

[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
stretch in the sling has little effect becuase there not much line there to stretch..

[/ QUOTE ]

Every little bits helps. Stretch in a block sling is beneficial to the climber.

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Is there any science to support statement Norm?

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http://www.yalecordage.com/videos
scroll down to the last vid.

Is there any science to support your statement Daniel?
 
Re: question about shock loading a rope and block

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Extra stretch in the sling creates (2x the stretch) movement in the piece which might even result in more force, dependng on the other factors...

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Can you explain how this can possibly be true? And what are the other factors?
 
Re: question about shock loading a rope and block

becasue the block creates a 2:1 system, any play in the sling, wether from leaving it tied loosly or stretch, will double the effect of the slop on the distance the piece falls. So 1' of stretch or play in the sling will create 2' extra fall in the piece. That can amount to a lot of force in certain scenarios.

I was wondering if there is any science to support the conclusion that extra stretch in the sling reduces shock loads, as it may be the opposite.
 
Re: question about shock loading a rope and block

During indoor demonstrations, we have caught wood with a dynamometer in the system. Even with an excellent ground person running the lowering line, the force on the dyno is consistently 6-7X. During the filmimg of 'The Art and Science of Practical Rigging, the results were right in line with that, a force of 6.5X, catching a 660 lb. ash log.
During lifting operations, if the 2 ends of the lifting rope are parallel, the force is 2X.
Widening, or increasing the rope angle, decreases the lifting power (can more work lifting), but also decreases the force at the block (beneficial for the climber and tree) during lowering operatons.
Daniel, this profession is dangerous enough. Why wouldn't you use every piece gear you have to put a little more safety into the equation? You use True Blue for rigging. Why not use a shock absorbing block sling as well, like Husky or Polydyne?
 
Re: question about shock loading a rope and block

Norm,
When you've been at this game for a long time, you learn to turn every little thing to your advantage, whenever practical and possible. And also that a lot of things in this biz are "counter-intuitive".. I would use the dynamic slings if I thought they would help reduce shock loads. The question is "do they"? We obviously know that stretch in the rigging line is a huge factor in reducing shock loads. However that does not mean that stretch in the sling will do the same.
 
Re: question about shock loading a rope and block

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...I would use the dynamic slings if I thought they would help reduce shock loads. The question is "do they"? We obviously know that stretch in the rigging line is a huge factor in reducing shock loads. However that does not mean that stretch in the sling will do the same.

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I have to agree with Daniel--intuition can be misleading. I'll go one further and say I love it when my intuition proves to be wrong and I learn a new thing. This is such a case.

After fiddling with this with pencil and paper for a while, I decided I should write a short program that would simulate all the features of dropping a load on a block. The factors involved are the stretchiness of the rope and the sling, the various dimensions of the rigging scenario, the weight being dropped, and friction in the pulley. I assumed a perfect pulley to make the problem slightly simpler. I also assumed rope stretch is a linear function of tension. This is pretty accurate when the range of tensions is modest, say 20% to 30% of rated maximum tension. So for the rope shown, Samson stable braid, the rope should be quite linear between 2000 and 4000 lbs. Here's a screenshot of the program:

RiggingSling.jpg


Bullrope: Besides stable braid I also tried a stretchier nylon double-braid.
Weight: In pounds, the weight to be dropped.
Height above block: In feet. This is before any sling length is added to the picture.
Block to Ground: In feet, distance from block to rigid tie-off. In the example shown we have 34 feet of rope to stretch (no sling involved).

Sling Length: In feet. This is the amount of sling hanging down below the anchor point. This number is added to the height above block number to give the true distance the load will fall, 9 feet in this case. When the rope and sling stretch as they stop the load, the load doesn't end up 4.5 feet below the block, but somewhat farther still. And of course the block moves downward as well.

Sling Stiffness: This is relative to the bull rope. In the screenshot we assume the two legs of the sling supporting the block have a combined stiffness 4 times that of the bull rope.

Bullrope Tension: This is the maximum shock load experienced by the bullrope at maximum stretch. Naturally the sling experiences twice this much.

The results of dozens of scenarios were consistent: Any sling length whatsoever increased the ultimate shock load. The longer the sling the greater the shock. And the stretchier the sling the greater the shock.

The numbers in the screenshot are for the rope alone. Including the sling in the calculation gives an answer of 2648 lbs., an increase of about 6%.
 
Re: question about shock loading a rope and block

I'm wondering why the trend in rigging is bigger faster? For example, while a rope like dynasorb might allow you to take bigger pieces, why? I've always felt comfortable with the size pieces I take - lived in Cali and did the euc-man thing - learned allot, and have come to realize that the only advantage I see to a rope like dynasorb is that it could give me a bigger safety-factor with what I'm already comfortable doing. Why go bigger just because you can? (and who says you can - the tree is the "ultimate" factor here - not the rope and gear) Each rope construction has it's function - learning to use them appropriately in conjunction with all our other cool gear is the "art and science" of it all :)

peace,

mk
 
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