Pretensioning Crane Picks

chris_girard

chris_girard

Branched out member
Location
Gilmanton, N.H.
Ok, the reason why I'm asking this question, is because I've heard different things from different climbers and I just want to throw it out there to get a wide range of opinions and reasons.

What do climbers like to use as a percentage when pretensioning the sling before cutting? I have heard anywhere from 30% all the way up to 100% of the estimated weight of the pick.

On trees that are dead and where the piece may break when in the air, I can see where going up to near 100% may be a good thing, so you can see if the crane can lift the piece safely.

Most of the time, I would think between 30%-50% would be good.

Any thoughts?
 
with our k-boom, i go to 100% and sometimes beyond at first to tighten slings properly, then back off below that, maybe try for about 90-100% and watch my kerf as I cut through. If kerf opening too much, back off more. IF kerf closing, add more pick up. Of course, recheck and make sure over COG and make sure that's not off and that that's not why its opening or closing up.
 
When I'm setting the slings, and especially true of multiple slings and/or dead leaders, I like to see a bit of a tighten up so I can tell where the strongest tension and balance is going to be. This is a basic cinching, not really a formulated % of load. For that, I like to see it tensioned to 100% of a conservative estimation of the load. I don't want to risk having an operator overloading the rigging; however, at some point during the cutting there will be a total lift of the load, usually just over 100% to generate an upward pull as the last fibers release in the cut.

Jesus, I'm starting to sound like the others . . . I feel like a goddamned lawyer explaining myself! Any post where I see the dreadful "and/or" being used, I know I've got an assh*le on my hands.
 
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Jesus, I'm starting to sound like the others . . . I feel like a goddamned lawyer explaining myself! Any post where I see the dreadful "and/or" being used, I know I've got an assh*le on my hands.

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LOL, you make me laugh, but I really do appreciate the advice.
 
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Tough question to answer.
For me, it depends on the weight, limb angle and how many tie offs there are. Most of the time 50-60% of the estimated weight. On vertical cuts, I'll go up to 75%.

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I'm with Norm....unless I was expecting it to slip, then I'd test the water a little more
 
Thank you everyone for taking the time to answer this question.

I know that its a tough one, with really no one correct answer. Every crane pick is different and to try and quantify it with a percentage is very difficult.
 
I take up the load until the ball stop spinning and the cable seems to be taught , if you take too much it will spring or kick when the rig takes the weight , and load weights are only estimates..The worst thing if its hooked right is the load renders or sits on the saw and thats a quick fix with the flick of the wrist I hand signal no radios ..
 
I learned early on from using the GRCS what a bad thing it is to overload a piece and have it pop right up in the air in front of me. Not a pleasent experience.

That is why I am conservative in my estimates when doing crane picks, maybe a little too conservative.
 
I try to be just under the weight then pick the piece off.With overlapping cuts it works real well(providing wood isnt too thick between the kirfs.
 
I popped one off before and it almost knocked out my teeth , the pic went up and down catching the side of the trunk and scaring the hell outta me ... Now I start the cut and adjust to the load as it renders .. I have seen a crane stand up before and its the most helpless feeling in the world , if you head down the crane may catch ya there and if you stay the boom may be on your skull..The newer machines are built to deflect alot ...I have worked with hydro and lattice type cranes and its all different ..
 
I have to say as gay as it sounds and I have been around cranes for a long time , the videos of you doing removals wearing the remote in the tree are incredible and its really hard to impress me with a crane video, I remember the first time that I watched one I sat with my mouth wide open , I am a true fan..
 
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Always 100% of the estimated weight, this way you test every component in the system(mainly the tree) before the critical point when you cut it.

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I think that is a very concise explanation. I can agree with that logic and for the most part, I'd say we do the same on a majority of our pretensioning.

But, we still have some different opinions with reputable guys here.

Would it be fair to say, "It depends"? It depends on limb angle, weight, potential targets below, the condition of the limb, coarse barked tree vs. slippery barked tree, diameter of the limb where the choker is placed, etc...

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Would it also be fair to question, "What is the minimum pretensioned percentage we should apply?"
 
I agree with Mark. Different types of cranes are different. There is much more boom deflection on a kboom.I think i still pretention it under the pick weight. There is much less movement to the side with a k boom yet it can stress the boom sideways more if the piece wants to move that way than having alot of load line out.
 
I still say 100% because first, you want to test everything to make sure the piece isn't going to break after the cut and second if your acurate with your estimate there won't be any movement after the cut.

If you underestimate the weight the pick will drop onto the slings, if you overestimate the pick then it will jump up.
 
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If you underestimate the weight the pick will drop onto the slings, if you overestimate the pick then it will jump up.

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Very good point classic. Here's a picture that was posted on the Buzz a few years ago, that shows a piece that was pre-tensioned WAY TOO MUCH and what can happen.

This was how high the piece jumped up to and you can see where it slabbed off in the back. The crane being used was a large 175 ton.

http://www.treebuzz.com/forum/images/upload/10326-DSCF25.JPG
 
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