Need help deciding on a heavy-duty rigging setup..

eyehearttrees

Active Member
1st, does anyone have the formula for dynamic weights that actually takes rope-elasticity into account?

Am hoping for help/suggestions/advice on buying a new rigging setup, I have medium-duty (1/2" line / 1/2" anchor rope holding rings up top and natural trunk-wraps down below is my go-to) but it doesn't let me negative-rig / block-down stuff (I aim to keep total-force to 1k lbs maximum so if I had to load the line from a negative angle(blocking down) I would be hitting 1k with the tiniest pieces so I pass on a tree removal if it's thick and I can't fell it where it stands....I've got to thinking that a few hundred $$ could be enough to rectify this but am hoping for brands/product/company suggestions and strength-opinions because I haven't heard a rule-of-thumb for stuff like canopy-anchors for blocking (I just see people use absurdly strong 3/4" or 1" tenex which I assume is overkill but unsure)

So am thinking something like this:

$230 for 150' Stable Braid (3/4" 20k MBS, ideally find just 100' though, quoting prices from Bartlett's right now am sure I'd find better deals)
~$100 for a rigging-ring anchor, this is where I'm most-uncertain about the strength I need, I mean a 3/4" tenex sling is 20k mbs as well so part of me thinks that means it's too-weak (when the bull rope itself is 20k), although since it's a 2-ringed device it'd be used in a basket-hitch manner which is doubly-strong compared to the single-leg usage of the bull-rope....really feel like 3/4" tenex / 20k MBS is OK for my anchor but uncertain, would go 1" if necessary!
$50 on some more of the big 2" nylon-webbing slings (I've got a couple now, know they're overkill but they still work great!)

Am also considering getting a tenex prusik to use on a length of 1/2" rope for 'spider leg balancing' of longer limbs so would probably throw that in...my first order was through Bartlett's and am hoping to try another outlet (treestuff maybe? I'm pretty anal about who I buy from and the price-gouging at the big-3 really bothers me so I'd like to avoid them if-possible, at the same time obviously I'm not using rope I buy from an ebayer lol!)

PS- To be clear, I'm planning to use this setup for blocking-down Oaks (quercus virginiana is the most prolific in my area, probably 1/3rd of the work I do) so still can't just do giant sections / will have to be sharp on my #'s for what the setup can handle, any&all thoughts on 'the formula'(for max-load on the rope) and considerations on shock loading would be greatly appreciated :)
 

eyehearttrees

Active Member
I think some of my problem understanding the #'s is the whole "WLL" thing, I'm finding it almost useless and am finding that I'm just using tensile/mbs and then appraising the actual use-case in front of me...was just browsing some of the rigging-gear mentioned above and kept seeing "WLL" values and mentally noting them until I realized "How the F can you post a 'wll' for an anchor when you haven't specified if it's getting shock-loads/negative-rigging or not?", LOL seriously it makes a world of difference whether that 200lbs section of trunk is already under-tension when you finish your cut, or it's going to free-fall for 5' before hitting restriction, how on earth can you have these WLL's for rigging anchors when there's no context of usage?

I feel like appropriate weighting is around 1:3 max, 1:5 being super safe, if you're only holding stuff (like you've got the branch anchored & tensioned from above before you cut it), I'd probably want to keep a 1:5 spread for falling pieces/negative-rigging *but* that's after doing a proper calculation of the weight of what I'm dropping....I imagine/hope you 'get a feel' for this quickly, I want to be able to drop large sections under-control w/o having to spend a while on each piece doing math lol I'm just not in that mindset when in a tree, figure I can either learn the right way until it becomes rote or I can just get stronger/larger gear (am betting it's smarter to do the former approach, to really understand the forces I'm placing at any time!)
 

eyehearttrees

Active Member
First rule of rigging. The lowering line needs to be the weak link in the system
Would love any elaboration on this you could give! So far as I can see it is *inherently* the weakest part of the system, in fact the connection from the lowering line to the sling(s) of what's being lowered should be the weakest point, the rope gets stronger as it gets longer (due to shock-absorption) and of course the anchors should never be in-question (even w/ the 3/4" bull-rope I still feel a 3/4" tenex sling would be sufficient so-long-as it's used in a basket-hitch IE using both ends of it, like with 2 rigging rings)

BTW I love your avatar it's the only one on this site I routinely stop to check out, always makes me wish I could hike anywhere worthwhile (I'm in coastal FL by Tampa so it's just marshy crap everywhere nearby!)

edited-in:
Second rule.. don’t break the rigging line
Do you think it's cheaping-out to get a 20k lbs line? The Stable Braid seemed like the most cost-effective choice, the Notch offering ('kraken' I think) boasted great strength-per-dollar but I've begun to lose faith in Notch's #'s on their products..
 

evo

Well-Known Member
20k is pretty freakin strong. It’s good for swinging around 2k logs, which is a huge amount of weight.
Unless your in a situation where you HAVE to go big just take smaller pieces.

Your block sees 2x the loading from your rigging. If you broke a block or sling/ring. It would sling shot the material risking life and limb.
While the lowering device sees less load it’s equally important.
That is why all good rigging with a 20k line would have a block/sling rated at 40k.. many have opted to go with amsteel for a sling but I think this is a poor choice as it doesn’t handle shock loads well
 

Joeybagodonuts

Well-Known Member
I think some of my problem understanding the #'s is the whole "WLL" thing, I'm finding it almost useless and am finding that I'm just using tensile/mbs and then appraising the actual use-case in front of me...was just browsing some of the rigging-gear mentioned above and kept seeing "WLL" values and mentally noting them until I realized "How the F can you post a 'wll' for an anchor when you haven't specified if it's getting shock-loads/negative-rigging or not?", LOL seriously it makes a world of difference whether that 200lbs section of trunk is already under-tension when you finish your cut, or it's going to free-fall for 5' before hitting restriction, how on earth can you have these WLL's for rigging anchors when there's no context of usage?

I feel like appropriate weighting is around 1:3 max, 1:5 being super safe, if you're only holding stuff (like you've got the branch anchored & tensioned from above before you cut it), I'd probably want to keep a 1:5 spread for falling pieces/negative-rigging *but* that's after doing a proper calculation of the weight of what I'm dropping....I imagine/hope you 'get a feel' for this quickly, I want to be able to drop large sections under-control w/o having to spend a while on each piece doing math lol I'm just not in that mindset when in a tree, figure I can either learn the right way until it becomes rote or I can just get stronger/larger gear (am betting it's smarter to do the former approach, to really understand the forces I'm placing at any time!)
Different nomenclatures for different industries standards & sometimes the lines between industries get blurred.. Industrial stuff will generally have a WLL based off a certain standard... Said standard may have a certain required safety factor 1:4, 1:5, 1:10, etc. Arb stuff is a completely different animal whereas it's not always static. The industrial stuff is generally meant & rated around static lifting.

At least that's how I've interpeted the majority of wll stuff. To be honest, it's way way deeper than what i just mumbled & a much deeper understanding is required in order to be safe. If you find yourself questioning the very basics of this equipment... or have never done this stuff, it's probably not a good idea to go as big as your thinking of going.. Shit goes sideways so fucking fast my friend...

Either way, the working load limit is the working load limit I'm my opinion.. idc if it's static or dynamic, I'm not trying to push past it.

I'm not following on this..
Why have you started to lose faith in Notch's strength ratings? In your experience, what has failed to meet the expected strength rating on your equipment???
 

Jehinten

Well-Known Member
A couple of points on what you've mentioned so far, I try not to figure out the total force when considering the stretch in rope. If you rig pieces as if using a steel cable and make sure that your within specs, then the rope stretch will only further add a cushion of safety. There's no reason to try and load your system to max each time.

Stable braid is a great rope and it was the first rigging rope I looked at due to its strength and reputation, anymore I prefer ropes that have more stretch and can handle some tree friction without glazing as bad even with some strength reduction compared to stable braid.

For rigging rings I often use 3/4" tenex or double braid for the host rope, even when I expect lower weight rigging so that I do not have to change out rigging slings as I go.

As for the wll, that is the amount of force that these items should see, not the amount of weight. If the wll is 1000lbs, that is 1000lbs at static or 180lbs dropped 5 feet (without running the rope) for near 1000lbs of force.
 

colb

Well-Known Member
Coupla things.

Tenex prussic might be the wrong material for a prussic. Might glaze...

What diameter oak will you be taking on? To be honest, sounds like you're in medium-size trees if you want to take 1k chunks. 5/8" dynasorb or husky would be good for that. If you're too close to the roof to use dynasorb, you're probably needing to cut chunks or use a crane. I like 150' because I can rig down a spar from 60' up and my ground guy has enough to play with. Energy absorption makes things safer, so try to get a bungee cord rope unless you really need something else.

Power on!
 

Birdyman88

Well-Known Member
I posted this in another thread the other day. Dynamic loading is not well understood, so many just don't bother doing the calcs. If you want to lower your risk, i suggest spending time getting familiar with these calcs. I just cut and paste the following from the other thread on the Omni Block 4.5.

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Man, I don't mean to ruffle feathers, and I know this thread is a few weeks old, but the math and dynamic load calcs in this thread are not correct, but unfortunately very common. Not picking on anyone here, because this happens in just about every thread discussing dynamic loading. Sorry, I've been commenting in another post about the calcs for dynamic loading and energy absorption being misinterpreted and misunderstood and this is a what I'm talking about.

Okay, so let's forget about the block for bit and just look at the rope and load. So here's how it's works. Load above block has potential energy, when load dropped potential energy converts to kinetic energy, when it loads rope kinetic energy is converted to spring potential energy and heat. So in the above, 4,000 lbs drops 6 ft to start loading line. That's 24,000 ft-lb of potential energy that got converted into 24,000 ft-lb of kinetic energy that's fixing to being converted into 24,000 ft-lb of spring potential energy and a tiny bit of heat. So all we know so far is the amount of spring potential energy and heat that will be created in the rope - but that tells us nothing about how much actual force will be on the rope. To find the force, you must divide the 24,000 ft-lb number by the 20% EA Factor that Yale gives you. So let's say the 20% EA is 400 ft-lb/lb. So (24,000 ft-lb)/(400 ft-lb/lb)=60 lb. That 60 lb is HOW MUCH OF THAT MODEL OF ROPE YOU NEED TO USE in order for the PEAK FORCE TO EXACTLY EQUAL 20% of THE ABS. Now, let's say that rope is 10 lb per 100 ft, so 60 lb of rope is 600 ft. So if I dropped that 4,000 lb log 6 ft onto that 400 ft-lb/lb EA rope and I had exactly 600 ft of rope between the load and friction device - AND I DID NOT LET THE LOAD RUN - the peak force would exactly hit 20% of the ABS. From there, you can figure out what the force would be on the block and rigging point. Now, to take it one step further, if I used the same model rope, but in a larger diameter, then I would not need as many feet of the rope to equal that same 60 lb requirement since the larger diameter provides more rope weight per 100 ft.

So what happens if you use less than 600ft in the above example, then your peak forces will exceed the 20% ABS. Let's say I only used 100ft of the 10 lb/100 ft rope between the load and friction device. That's 1/6 of what I should have used to keep the peak force at 20% ABS, which means I should have used a rope with 1/(1/6), or 6x the EA factor, or alternately, a rope with 6x the weight per 100 ft. Since I did not use a higher EA rope, or a heavier rope, but the 400 ft-lb/lb, 10 lb/100 ft rope, then I generated a peak force that was the square root of 6, or 2.45X times the 20% force, or in other words I just put a peak force of 48% the ABS on that rope. Let's look at another, since we're blocking down. Let's say I only used 30 ft of rope between the load and friction device, then 600 divided by 30 is 20, and the square root of 20 is 4.47, and 4.47 times 20% is 89% of the ABS. In this case you just hit the MBS dropping that load. So, where did the "square root" come from? Hang tight, I answer that below.

EA factors are specific to each X% of ABS. Meaning there is an EA for 10%, another EA for 20%, another EA for 30%, etc. Yale only publishes the 20% EA because that's the percent loading we have accepted out here in the industry. If you wanted to use 10% load max, you would have to talk Yale and the other manufacturers into providing it to you. Or, if you understand the elongation curves (% break vs % elongation), then you can actually derive it on your own. Raw derivation however gets complicated so I won't get into it here.

So, to derive a different EA from a 20% EA that you already have, here's how you do it. Energy Absorption of the rope is really just the area under the curve of Force vs Elongation normalized to 1 lb of rope. In calculus terms it is an integration to find that area. So if my Force vs Elongation curve is linear, then the integration yields a 2nd order function, which means we have an x-squared in the equation. So EA is then a function of the SQUARE of the percent break. So if I know the 20% EA, then to find the 100% EA, I divide 100% by 20%, get 5, then square 5 to get 25, then multiply 25 times the 20% EA, and I now have the 100% EA. If you look at Yale Polydyne with a 576 ft-lb/lb 20% EA, and you want to estimate the "Red" Ultimate EA, which Yale appears to be refering to the 90% break (i.e., MBS) then you divide 90% by 20% to get 4.5, then square 4.5 to get 20.25, then multiply 20.25 times the 576 ft-lb/lb 20% EA and you get 11,664 ft-lb/lb 90% Red Ultimate EA. Yale actually publishes the Red Ultimate EA at 11,187 ft-lb/lb. The minor difference would be attributable to the fact that the Force vs Elongation curve is not perfectly linear, over the graph.
 

Birdyman88

Well-Known Member
And a follow up post with another example.

***************
I thought 4,000 lb was normal for some of you guys, lol. But, here is a more real example that might surprise some people. Your rope is Yale Double Esterlon 5/8. ABS 14,900 lb, 13 lb per 100 ft, and 20% EA of 265 ft-lb/lb. Really strong stuff. You have no reservations putting a 1,000 lb piece on this stuff. So you're blocking down a big water oak, and you just got below the two leaders and now you're looking at 30" diameter wood 20 ft above ground. Porty is waist high at 3 ft. You want to take a 3 ft piece of the stalk, which you have determined weighs 945 lb. You'll tie a running bowline followed by a marl. The COG of the section is 2 ft above the block, which means the load will fall 4 ft before loading rope. You are totally confident the Double Esterlon is plenty strong.

Okay, so now lets do the math. 945 lb load times 4 ft drop is 3,780 ft-lb of energy. Next 3,780 ft-lb divided by the 20% EA of 265 ft-lb/lb yields 14.3 lbs of rope needed to stay below 20% ABS. Now divide 14.3 lb by 13 lb/100 ft and you arrive at 110 ft of rope required. We already know that we can only have 18.5 ft in the system since the porty is where it is. So we need 110 ft, but we're only giving it 18.5 ft. Now, how many of us actually know whats fixing to come next????

Okay, so we are only using 18.5/110, or 17% of what's required. Another way to say this is we need an actual EA of 110/18.5, or 6.04X the EA of D-Esterlon. Or we need a larger D-Esterlon rope with a cross sectional area 6.04X that of the 5/8 - this equates to a 1-1/2" rope. But since we have neither, let's see how much force will be put on our 5/8. So, if we take the square root of 6.04, we get 2.45. Multiply that by the 20% ABS for the EA, and you get 49%. So that means that drop put 49% of the ABS, or 6,832 lbs of force on the rope. And, it only gets worse as you work your way down the stalk.

Does that surprise you? It did me when I started running numbers on loads. I sure don't take any sizeable loads for granted when I negative block. It also doesnt surprise me why ropes break in this business.
 
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southsoundtree

Well-Known Member
You'll tie a running bowline followed by a marl. The marl will snug about 1.5 ft above block, which means the load will fall 3 ft before loading rope. You are totally confident the Double Esterlon is plenty strong.
It's late, late and I just skimmed a bit...


The distance from the Center of Gravity of the section above the rigging block, not the distance from block to marl, is the important thing, right?

I think there is a diagram in the Art and Science of Practical Rigging, maybe.




Vertical speed lines onto armored/ padded areas can save some negative blocking, too.
 
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*useless info*

Well-Known Member
i think you are looking at elastic length and braking run to handle massive forces shown.
>>can try other factors like making it bust thru branches to slow down or controlled run to ~500# ground concussion to snub out rest of 'cigarette' into ground after lowering and limiting forces to
>>also 1000# is nice round number, but a lot of meat for such a folding drop.
>>less elastic rubberband(rope is rubbery/stretch compared to other elements in system) maintains forces and delivers to all connected points in system.
Don't have very many positive views of negative rigging of any real size
>>try not to do and to minimize distance between 1st hitch and catch of block hitch if do, do this doodoo.
>>if short load; can force hinge more slowly usually for more buffered delivery from hinge to line>> but short stubby pieces are harder catch.
>>playing that slow arc game on a CoG farther away can give very scary hard leverage forward/snatch doing this tho
To incite thicker hinge can pull with high line to top of load, can hyper tighten line and prussic pull line half way between support and load hitches/in face to pull across on rope to force hinge
>>can also use semi trailer truck tire changing 'spoon' to fit into kerf and give tempered steel lever
i also tried to sometimes drop bod hard backwards against hit to balance forces of both our timed hits more inline down stem support in mediums, in huges like this mite rather me to side somewhat of hit axis.
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Know your ropes>>Fresh ropes will have more elasticity than beaten lines
>>softer/feminine elasticity gets miffed faster usually and leaves line earlier in life before macho strength element fades.
After a hard hit may take line hours or over night to recover 'hysteresis' to same elastic dampening response to loads. So same trick immediately after can have different consequences in this game. Lunch between can tilt board more your way(but can require down/up trip..). Logically can't remove too many huges in 1 day playing that game
Especially when hyper pre-tightening, to then catch w/o run; hammering the hell outta the line!!
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Consider drops or crane, rather than control all for this like this; is safest. Playing this drop/invert/catch game raises mortality rate. RiP pioneer/scientist/contributor/benefactor/engineer Peter S. Donzelli; legend has it called it right, but ground crew did different and cost his life simply by taking 5 half circle arcs not reqeusted 3 on rope brake device. Even if not totally true, still ground control is a variable...
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Elastic length to first real frictions is the amount of elastic rubber band in system.
>>minimized when catch load high, more as line is lowered to be longer elastic device>> after you need it for primary hit...
Some buffered run can emulate this elastic dampening w/o hammering elasticity.
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Line strength is double edged sword; the stronger it is, the less elastic dampening extruded by same loading.
>>whereby if have same 10k line w/same 1k load >>convert 10k to 2:1 w/pulley on load
But now each leg is loaded 500#, instead of single leg 1000#
>>will get less elastic response of buffering peak pulses etc.
>>same thing happens when go up ladder to next strongest Arboplex or StableBraid etc. So jumping to 50:1 swl (extreme example) can make much worser in dynamic hits!!
>>(opposite direction)for smaller stuff off smaller stuff liked keeping elastic mountain/rescue line for rubbery dampening and slide off baby branches that couldn't take much more>>rope must fit job!
Continuing pulley theory to overhead supports:
>>IMMENSE side forces possible if spread support points to pulley
spread from 11:30-12:30to catch 6:00(each support leg 15 degrees from load centerline) load gets 25% of line hit as side pull to each support >>again as line lowers to more elastic length, the support angle is also more favorable, BUT only after initial hit!
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For rope turns and hitch points if no favorable taper or deformity, would make own with baby faces/humboldts cut to load and support as rope beds at rear rope arcs favored , straight side of cut against loading direction. Especially short, stocky. wider than long harder to hold pieces.
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Capstan, bollard, Porty etc. rope brake devices give predictable frictions, and act as heat sink for those frictions. Capstan math shows same brake force or 2" vs. 24" drum; so capstan size is to strength of capstan, soft arc of rope bend, thermal dilution and amount of heat sink, not brake force. So see branch frictions same, only as thermal insulator and smaller branch is higher concentration of that in smaller area as delivering same brake force... High friction point at redirect of ring support, bark rub etc. reduces loads to support because lowers loading to control leg, but reduces the elastic length of rubber band buffering presented to system.
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edit: CoG to block hitch point as hinge is load and hold, cosine vertical value doesn't change with height of CoG, only sine/horizontal val statically. Catch/hit is more vert. Larger turn arc of CoG is where this force cranks up thru hinge as rigid attachment. Total displacement shock val is CoG start to CoG finish, double height of CoG to block hitch point. As controlling value try to keep rope hinge distance of hitch(load) to hitch(block) short i think tho for tighter fold.
 
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Birdyman88

Well-Known Member
The distance from the Center of Gravity of the section above the rigging block, not the distance from block to marl, is the important thing, right?
Yes, it is COG start to COG finish. The above example now reflects that.

There's like infinite info on this stuff in the treebuzz archives
I saw some stuff out here on this one time, but there were a bunch of questions but nobody got anywhere with it. I'll go back out and look again.
 
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Tom Dunlap

Here from the beginning
Administrator
Thanks... huge thanks!!!! To the folks who wrote so much on this thread.

Lots of good info in the Archives...do some sesrches

Three excellent books to read:

Jepson ‘s To felll a tree
Blair: Arborist Equipment
Donzelli via ISA: Art and science of practical rigging

Having books puts the info in your hands to study. More important is all of these books were proofread by many people before publication. They are ‘The Truth’. Concise and accurate

ABE books is an excellent source of used books
 

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