Rigging forces and angles

[Pete Mctree]

Very useful info Pete.

Are you at liberty to divulge where its from.

Pm maybe?

 

Cheers

 

I was given them whilst in Oz. I have no idea of there origins sorry

[Bundle 2]

Hey treediver

would be pleased to get isbn/ref or othern useful info on that vid eh mate!

[treediver]

I looked everwhere for this DVD.

Theres only a few places sell it in the uk and its not cheap. But thats whats you expect from a training aid like this.

 

Proclimber sell it

http://www.proclimber.co.uk/catalogue/index.php?main_page=product_info&cPath=33_59&products_id=301

 

Bloody expensive from there.

 

Direct from the ISA us shop

http://secure.isa-arbor.com/store/The-Art-and-Science-of-Practical-Rigging-P268C40.aspx

 

But finally go to

http://www.totalarb.co.uk

http://www.totalarb.co.uk/cgi-bin/products.cgi?fa=catlist&pid=60&cmpid=54&cmrid=1

 

They are waaaaay cheaper than proclimber ..over £100.00!!!!!!!!!

and at £115.00 you wont find this dvd anywhere cheaper.

Its even cheaper than buying direct from the ISA even if your a member.

The book comes with the DVD aswell.

[Tom D]

Found this as well last night, very useful for pulling a stem over. Don't know whether link will work

 

Did this on 41 as well, you can use these setups to raise limbs when lowering if you hav'nt got a Hobs / GPRS

[TreeSpyder]

A few things to remember is that you can't just beat force; you pay or equate for every drop of it; it is never created nor destroyed; just transferred etc.

 

Also, that the minimum loading/base is the load itself, and this is at inline. Anything not inline is leveraged.

 

Wood, is basically inflexible. 100# inline at 10' or 20' is the same. But, at any angle the distance makes a difference. What we do; is calculate maximum/potential loading; which is perpendicular/90 degrees. So, 100# at inline is 100#; but it's maximum potential is the 100# X the distance 10' or 20' etc.

 

For, all angles less than 90/full potential; we multiply the cosine of the angle X the potential. The cosine of 90 is 1. So, full potential X 1 gives full potential. The cosine of lesser angle is less than 1. Like, .5 for 30 degrees. So, 20' X 100# gives 2000'#s potential X .5 gives the leverage at 30 degrees. (notice that at 1/3 tilt, half the leverage potential is achieved!). Also, at 30 degrees, the 20' spar reaches 10' from it's base!

 

Flexibles like rope is different. You have to take the cosecant or 1/sin of the angle X the loading. Length doesn't matter. The angle is the leg from inline. So, if suspending a weight between 2 poles; we cut the load in half(2 supports); then calculate the angle of each leg from inline/ minimal loading. So, in a perfectly centered weight between 2 poles; that would be an angle of half the spread of the lines. If 1 is higher than the other and or not centered weight; then we calculate half the load per leg; of angle from inline(given poles are higher than the load). If, the load is on a pulley; then the lines could equalize; if not, they could carry different tensions; but would try to equalize by adjusting their angles to overall minimum loading.

 

Impacting is different. It is weight X speed (distance over time). So, i try to pretension lines; then tip load slowly over into them; then give wide face and try to make the load itself, give final pretension to the line as it tips on hinge. i also favor slowly pulling over the load with rope etc. to force a stronger hinge; as well as acting as final pretightening. Note the line only tightens more as the load's hitchpoint moves away from the support point. Sometimes i will even make the load tip left against a right support, so the line tightens up so much; it hen pulls the load right; as i also adjust the backcut to allow. this gives a tighter line, than if ya just tipped load to the right many times.

 

Hope this helped. Some call the cosine of 90 Zer0; but ultimately we mean to find at what point leveraged fully = 1 (0 or 90 depending on how ya look at it). Then work the angles of part of a multiplier of 1 to find the leverage and reach of the spar at a given angle. Also, 100# on the end of a 20' spar is a perfect example. Real life is length from hinge as pivot to the Center of Gravity X the weight.

 

-KC

[Log-ologist]

Dont dump wood on ropes. Try to let the wood weight the rope gradually. If in doubt, use a stronger rope or a smaller bit of wood.

...Jamie

 

In many cases in the UK situation several small drops are faster than one big drop. Its safer , takes less time to rig and is more easily cleared on the landing. Climbers are usually only concerned with getting wood down fast ,not the speed of the whole job start to finish.

[Andy Collins]

QUOTE=Log-ologist;28048]In many cases in the UK situation several small drops are faster than one big drop. Its safer , takes less time to rig and is more easily cleared on the landing. Climbers are usually only concerned with getting wood down fast ,not the speed of the whole job start to finish.

 

well said!!

[RPA]

Found this a while ago and posted on another thread. Table on page 3 gives a good easy rule of thumb for rigging.

 

http://arbtalk.co.uk/forum/showthread.php?t=471&highlight=rigging

[Pete Bannister]

Hi’ just joined your forum as an interested amateur.

I’ve viewed the various links referred to in the comments on this thread and I'm a little mystified as to why arborists appear to use a simple pulley block to lower large loads. The mechanical advantage gained from using a simple block is only from the increased length of rope used to absorb the force. Depending on the rope and the length in which the force can be applied, internal friction and elasticity will absorb a considerable degree of the initial dynamic force. (This fact doesnt get mentioned in some of the links refered to but its a major means of energy absorbrion in any rope system.) Clearly, I can see the point of using more rather than less rope length. However, if you use a compound pulley system (traditional block and tackle) in place of your single pulley you can easily reduce the resultant load to be resisted at ground level ( x 4 or 5 easily). It would also reduce the resultant high-level load (the load on the tree and the strop) by the same factor if the rope is allowed to run through the system whilst breaking. I’m wondering, is it the weight and awkwardness of raising a compound pulley system into the tree, or would snagging be an issue? Hope my point is not too stupid!

[Pete Mctree]

Hi’ just joined your forum as an interested amateur.

I’ve viewed the various links referred to in the comments on this thread and I'm a little mystified as to why arborists appear to use a simple pulley block to lower large loads. The mechanical advantage gained from using a simple block is only from the increased length of rope used to absorb the force. Depending on the rope and the length in which the force can be applied, internal friction and elasticity will absorb a considerable degree of the initial dynamic force. (This fact doesnt get mentioned in some of the links refered to but its a major means of energy absorbrion in any rope system.) Clearly, I can see the point of using more rather than less rope length. However, if you use a compound pulley system (traditional block and tackle) in place of your single pulley you can easily reduce the resultant load to be resisted at ground level ( x 4 or 5 easily). It would also reduce the resultant high-level load (the load on the tree and the strop) by the same factor if the rope is allowed to run through the system whilst breaking. I’m wondering, is it the weight and awkwardness of raising a compound pulley system into the tree, or would snagging be an issue? Hope my point is not too stupid!

Your point is more than valid, and thanks for posting it.

 

The use of a pulley serves three functions for me- firstly in the absence of a natural crotch, secondly to protect and therefore maintain the structural integrity of the rope (most double braids have relativley poor heat resistance) and thirdly to ensure a predictable amount of friction so making the rigiing and running of loads more predictable therefore smoother and safer.

 

I have used compound rigging systems when lifting , then subsequently lowering loads. The main issue i had was the exra rope in the system made it vey elastic thus difficult to manage. If there was a long fall height for the load this could be of massive benifit, as the load could be allowed to run, and i will have to have a look at it again and treat this as a positive.

 

Some great food for thought - thanks