Bend radius for rigging

[TheTreeSpyder]

When said handed down, meant surviving chain of custody to that point written;
yes that which was used at the time.
i think Ashley shows seeing these great friends slipping away around the corner of the 1900 century mark and trying to capture his present and what losses he already was seeing before all gone. Was trying to seek out and find to preserve things lost even before his own time, and then his time too, to avert further loss.
Thank Goodness !!!!! His work is a key pivotal, so that we would be further behind , not ahead without ABoK.
i think our intellect, even connecting/stringing together ideas/properties/amount evolved with knotting as a most formable material of utility. Nothing else could take rock and stick for hammer, so to spear, with rope handles, hung on rope belt, with clothes tied on eventually even skins tied to feets as shoes evolved.
.
i think round host is key, and takes things from a distance to a degree perspective.
But, a smaller host would concentrate same wear stress to smaller area, and so expresses wear more emphatically and most noticeable if shared out to RT/'double bearing'(ABoK) on host.

Side Note also while here: small host with Bag/Groundline of nip above center crossing of Clove form, has more chance of riding higher into/towards greatest/greater nip region of the 2/1 pulley pull position at apex of arc. May even be better than double bury nip of Constrictor to side sometimes; especially if also folded/bunched as a slip to express even more boldly at the key nip point of top nip(lesson#1663 as greater/greatest nip more than #1662,1664) in Bag.

I can't find it in a quick image-search now, but there is a now pretty old (1980s?) knots-strength table produced IIRC by Samson showing --unusually, despite its relevance!-- the Anchor Bend (aka "Fish.BEND") & 2HHitches (again, IIRC, it was this sans a "round turn") for both a 5/8" ring & a 4" (?!) spar in, hmmm, 1/4"(?!) rope :: the former was weaker on the ring, and a bit stronger on the spar. .:. My surmise (all I got) is that on the larger dia. object the Anchor Bend pulled out enough tail so that its SPart ran pretty straight into tangent contact & around, whereas the 2HHs would give some bite into the SPart and have more weakening (though IIRC the diff. wasn't all so much).
Interestingly, in his first writing on knots --The Sailor & His Knots(?)-- in 1926 A. opined that the Anchor Bend should be finished w/HH and then the tail seized to the SPart ; that this would ensure that the turns didn't tighten around the anchor and ... have that wanted double bearing, really, more like a double eye knot than an hitch. --though this opinion seems to have been forgotten on writing ABoK decade plus later.

i look at this particular effect as a single or double Half Hitch(HH) slides down the firepole of SPart to seat at host and shear again across the SPart as a support column at ~90o/Samson angle on pillar. the direction of pull in usage of the HH makes all the difference, such as a termination HH pull across at 90 or a continuation/bend type of prefixing a Timber to make Killick that pulls along , not across a length.
A HH spaced away from host pulls along not across SPart support column like a prefixing HH in Killick, then seizing or perhaps even friction hitch to keep HH floating off host if can as it buffers force to the seam of seizing/friction hitch, both forms that would deform primary support column of SPart the least/if at all. This increase in efficiency/strength from more inline legs, of more towards 2 independent legs of support w/o deforming primary, at a loss then of some grip on host that a single Turn slid down the SPart and shearing across SPart column would give more of.
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i think this model is as the BullsEyes(termination) similar to later "Shells" and then DeadEyes(dead as in non turning pulley type position of redirect) presented in ABoK. The BullsEye is/was simply roundish oval to thread around and seize back to self making a strong seam w/o harsh bending/deforming of SPart to weaken, so then attack next weak point of not a smaller, harsher connection/termination but softer diffused/larger round than self or rail etc. So this is what i see in BullsEyes, DeadEyes and Shells: larger diffused, softer round joint/termination after not bending SPart otherwise.

knudeNoggin lends can't maximize both lessons at once w/RT on host and SPart.

kN can't make sense of what he's doing in this sentence! (-;

*kN*

Believe taught can't capitalize on
.
lesson#1720 :
"The ROUND TURN AND Two HALF HITCHES
is named by Steel in 1794. If a spar is small a round turn is preferable to a single turn. It makes a stronger knot and dissipates the wear."
&
lesson #1669 with RT around SPart
"The FIGURE-EIGHT HITCH and round turn If the rope is weak and the hoist is heavy, a Round Turn on the Standing Part adds materially to the strength of the knot."
.
At the same time. i figured this would be/named as due to further loss of tension from RT friction on host(rather than single/simple Turn) not enough /as much to grip SPart w/RT for the #1669 effect that would pull more along the SPart as a support column more like splice or rack, than shearing across same SPart support column with a simple/single Turn like in Half Hitch at Samson angle.
.
i do believe as i have played with this , that i do see some more proper along the SPart column pull by RT on SPart(#1669) even after RT on host(#1720), when positioned as for BullsEye #1533 of holy grail of not pulling across 'sacred' SPart as primary support column, but along with it instead most properly reaching for 2x strength if could. That leaves the arc as the Achille's Heel, so softened by larger round and perhaps also spreading out wear as shown in lesson#1720 for more surviving/stronger knot by consideration of less wear on the now double bearing on the opposing side of host from load pull.

Always a pleasure and expansion, ty.

 

[knudeNoggin]

We should pause this at :: (1) book assertions are often bunk ; (2) these structures haven't been tested (and in a variety of materials --cordage & tied-to object).

Re the more-material-to-spread-the-load, with a round turn, this puzzles me in that irrespective of the number of (round) turns after the SPart's initial turn onto the object, there yet IS still that initial turn --same forces, et cetera. The "tensionless hitch" has been promoted as somehow kinder to trees (for rockclimbing top anchor); but if anything, it is worse, as the follow-on wraps simply give more material to elongate under load and to ... have more material of SPart flowing out and abrading --in contrast to the hugging of two legs of an eye knot, each having half the force of a hitch, and neither moving much against the tree.

*kN*

 

[Bart_]

When I watch you guys talk, I feel like I did the first time an instructor said "hold the guitar like this, press your finger here on the string and pluck it with the pick - twang..." So much water flowing under the bridge to get a handle on. I'll keep trying. Appreciate your knowledgeable inputs.

 

[KentuckySawyer]

I was taught long ago to maintain a 4:1 ratio when running lines. Anything less could damage the rope with repeated use. For a typical 1/2-inch rope, you’d need at least a 2-inch diameter for your pipe, bollard, pulley, or ring. Has the industry standard changed? I see guys running 3/4-inch lines through rigging rings on a regular basis. A local here rappels off a single carabiner when doing crane work. Has the standard changed or is it just being ignored?

Don’t get me wrong, I’m no purist. I’ve certainly used a figure eight, friction savers, and smaller than 2-inch rings and pulleys with 1/2-inch line in various applications for decades. I just try to minimize the less than 4:1 ratio use when loading the a line with a significant load. For me, “significant” with 1/2-inch is more than a 500-lb static, or a 200–lb dynamic load.

Most of the ropes people are using are so overbuilt that they can get away with ignoring "best practice" guidelines. There might be some truth in the posts above, but who's going to sift through all that? Personally, I'm comfortable bending most ropes rigging ropes 180 degrees over a good sized rigging thimble. Rappelling off a single carabiner isn't for me, but I doubt the rope will break because of it. Might wear out the biner though.

 

[Muggs]

I have a question about impact rigging block design. Most (all?) have what DMM calls an “anchor thimble” to improve the bend ratio but it’s significantly smaller than the main sheave. If I want to follow best practices and use a larger sling than my rigging rope this makes the bend ratio very unfavorable on the anchor thimble. Why wouldn’t designers want a 4:1 ratio on the thimble also? Is this to prevent users from getting the ends mixed up? Save weight and keep the cost down?

Maybe it's a little ok to scrimp on the thimble because there's no motion there.

I have wondered about this question for a long time as well. The only possible answer I can come up with is that the tension and compression of rope fibers around the sheave is quite different when the rope is moving (ie load line) vs. stationary (ie sling). Does anyone know the mechanism that explains why this would be? Part of me thinks that if I'm using a half-inch load line on a good block with a 5/8" sling, the anchor thimble should be larger diameter than the main sheave...

 

[Shadowscape]

The rigging rope is moving, and with it going over a bend the fibers have to shift. The outside ones space themselves apart and the inner ones need to bunch up closer together. And they have to move under extreme pressure. The larger the radius the less shifting under this load needs to be done. The sling on the upper one is not moving so the fibers don't have to shift under load.
It is not an issue of distributing the weight over an area, but fiber shifting under pressure.

 

[Muggs]

Fair enough, but the sling is seeing twice the load of the rope, and in a negative rigging situation the fibers on the sling are going from zero load to max shock-load in a small fraction of a second, jammed up against that small anchor thimble. There must be shifting of fibers when the sling goes from zero to 100 like that?

 

[Shadowscape]

Fair enough, but the sling is seeing twice the load of the rope, and in a negative rigging situation the fibers on the sling are going from zero load to max shock-load in a small fraction of a second, jammed up against that small anchor thimble...

Have you had one break?
The heat from the fibers shifting under extreme pressure is going to take a much greater toll on your rope than the shock load on the sling.

 

[Muggs]

No, but I've never broken a rope in my rigging before either. Only broken ropes I've seen were from pulling with trucks, redneck style

 

[Shadowscape]

Your block there in the photos is for a 1/2" rigging line with a 9/16" sling.
I bet your rigging line will break before the sling does if pushed beyond its design limits.

 

[Shadowscape]

Of course, it would be a tough experiment as the load would have to be running during the test rather than a straight pull test. But an interesting idea to ponder. If you ever do decide to try that experiment, you can't borrow one of my blocks though.

 

[Muggs]

I agree that my rope will break before my sling does. Slings are usually made these days from fibers that are stronger than the load line, in addition to being larger diameter cordage. I guess it's just my general observation that anchor thimbles seem undersized in a world where so much emphasis is placed on sheave bend radius. I had not thought about the heat generated by the fibers shifting under pressure, that's a good point.

 

[Bart_]

Related to the heat generated is the heat capacitance of what you're heating. It's a case of input heat energy = how much degrees temperature rise where the rope fiber strength is dependent on the degrees rise. Power is motion x force, stationary the motion gets very limited vs travelling around a pulley or biner while the forces remain roughly comparable in order of size. My take. Pondering actual quantitative values is where it gets interesting, or realizing some new gotcha effect in a process.

Ponder - where does all that energy go to get a tension ratio? Heat. Aha could become quantitative any time now

Classic example was a guy on here natural crotched a top with an "adequate" rope but the stretch on taking the load skidded the rope in the crotch under load, heat, snap was the theory. You can snap dyneema throw lines over a crotch via skid heat weakening as you tug the stuck bag. How do I know. ;(

 

[TheTreeSpyder]

Dynamic changes in where arc bends as an impact vs. change factor at rest. Somehow as like terminating vs. flowing electric, water, air etc. thru their force channeling devices. Force going to arc vs. cranking around it.

 

[Vicente]

No, but I've never broken a rope in my rigging before either. Only broken ropes I've seen were from pulling with trucks, redneck style

Making me feel judged over here.

 

[Friedrich]

I agree that my rope will break before my sling does. Slings are usually made these days from fibers that are stronger than the load line, in addition to being larger diameter cordage. I guess it's just my general observation that anchor thimbles seem undersized in a world where so much emphasis is placed on sheave bend radius. I had not thought about the heat generated by the fibers shifting under pressure, that's a good point.

i have made the same observation regarding anchor thimble size and think that is one of the beauty‘s of rings.

i‘ve snapped two slings (3/4 tenex) during dynamic rigging, and rope only while pulling (non critical) i think the sling is more often the weakest link than people realize.

 

[southsoundtree]

What rope in that rigging?

 

[Friedrich]

if i remember correctly it was 5/8“ sirius.

 

[Muggs]

I think the sling is more often the weakest link than people realize.

Keep revisiting this concept for a project I'm working on, and I agree 100%. I think the sling is very often the weakest link in our rigging systems.

Don Blair's Weak Link Law: "the lowering line itself must be the weakest link in the rigging system. All rigging components, i.e. blocks, slings, connecting links, must have safe working loads in comfortable excess to that of the lowering line employed".

For terminal rigging, it's not enough to just make the sling "one size up", or even 2 sizes up, from the rope, especially with double braid slings. It should really be double the tensile of the rigging line being used. This probably forces me to use Tenex, even when I would prefer a double braid sling.

In my neck of the woods, 5/8" rigging line is as serious as it gets. There's nothing I would get into that would need bigger. So 5/8" Sirius is rated at 14,200 lb, while a 3/4" Tenex-TEC sling is "only" 24,800 lb. Feels a bit nuts to say that a sling rated for almost 25K lb is undersized, but with heavy, terminal rigging, once you get into shock loading and such dynamics, it really is.

 

[Muggs]