Spider leg length (?)

[Chris Schultz]

I’ve got a 30’ piece of 3/8” tenex I picked up for a spider leg. I intend on cow hitch or running bow, coupled with taughtline hitch onto primary rigging line. Before I cut mine I’m curious about how long are peoples spider legs for limb balancing? I rarely have a need to deploy this, but I figured for the cost of the tenex it couldn’t hurt to have in my rig bag...My only real life experience is the piece we have in the tree service truck which is annoyingly long, and it’s not mine to cut..... thanks

 

[Reach]

We use a set of 20’ and 25’ spider legs for lifting and balancing, we’re using 3/4” Ultrex now, but we still have some 3/4” double braid as well which we use for smaller picks.

 

[Jehinten]

I bought one from Wesspur a few years ago at 20' long. It works pretty well, although doesn't get used often. It's a bit long for short trees where the friction hitch gets into the rigging point, but the excess tail can make for a short tagine to help it around obstacles

 

[Stumpsprouts]

That will be a great balancer. I find that under 20’ is not very useful. In those moments there is excessive tail, you can daisy chain it to keep it out of the way.

I have two such slings, one 25ish and one 15ish. I almost never use the short one.

I would keep it at 30 and cut it after a month of use if the tail really bothers ya.

 

[TheTreeSpyder]

What angle spread range y'all use?

 

[Stumpsprouts]

What angle spread range y'all use?

I’d say it’s often around 120, not often wider, sometimes around 90. Would love to learn others answer to that, good question!

 

[TheTreeSpyder]

​

090 spread is 45degrees spread each leg from centerline .
120 spread is 60degrees spread each leg from centerline.
2 support legs to centerline is 50% load each.
As support legs deflect from centerline
>> they are less efficient support columns require more tension for same load.
>>they also incur inwardly crushing side force, that leverages harder against weakness and deformity.

Deflection	Load​	Per leg	/cosine	=tension	X sine	=side
45	1000	500	.707	707	.707	500
60	1000	500	.500	1000	.866	866

Above finds tension from support column needed per leg divided by cosine, then finds side compression by multiplying tension X sine.
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Below shortcuts from support column needed per leg X tangent to find side compression without going thru tension calculation.

Deflection	load	per leg	skip	skip	X tangent	=side force
45	1000	500			1	500
60	1000	500			1.73	866

Side force escalates very rapidly flatter than 120 spread benchmark, more than doubling at 150 to 1866!!

 

[HigherGroundArborist]

I agree with @Stumpsprouts, longer is better. As I often tell my clients, “Whatever you decide, there’s no gluing it back together.”

 

[tek9tim]

I don't have much intelligent to add other than it's super easy to splice an eye onto the end that'll connect to your rigging line and use a klemheist to attach instead of using a tautline. A tautline is super easy too though.

 

[Chris Schultz]

I don't have much intelligent to add other than it's super easy to splice an eye onto the end that'll connect to your rigging line and use a klemheist to attach instead of using a tautline. A tautline is super easy too though.

I kinda dislike the klemheist ONLY because the whole tail needs to be fed through your wraps.... But if I do splice an eye in it, what dimension do you recommend? Rigging line 1/2”-5/8”. Tenex sling 3/8”

 

[tek9tim]

I kinda dislike the klemheist ONLY because the whole tail needs to be fed through your wraps.... But if I do splice an eye in it, what dimension do you recommend? Rigging line 1/2”-5/8”. Tenex sling 3/8”

Yeah, that’s a definite downside. I don’t recall what I spliced mine up at. IIRC, I just doubled it up and wrapped it around my rigging line and came up with an eye length that worked. And I don’t have my rigging gear handy at the moment to measure.

 

[dmonn]

When you splice tenex with a locking brummel I've heard you lose some significant strength (40%?). I think there's an alternative where you pass the bitter end through the standing end, then bury the tail. It's a long bury, but pretty easy to do. That supposedly reduces the loss of strength. But I'm definitely not an expert.

 

[Brocky]

If you just used a locking brummel with no bury it reduces the strength by half. With a proper bury it only reduces by 5-10 percent. A bury only of 3-4 fid lengths can get close to the break strength of the rope if reduced and tapered correctly.

 

[Phil]

I’d say it’s often around 120, not often wider, sometimes around 90. Would love to learn others answer to that, good question!

You'd have to invert your perspective on this configuration but the math should be the same.

 

[Stumpsprouts]

You'd have to invert your perspective on this configuration but the math should be the same.

I’ve seen this. Good stuff. My understanding is at a 90 degree angle it’s roughly 70% of the load on those two points, at 120 degrees roughly 100%, and over 120 degrees you increase past 100%. Since the general purpose of a balancer added to rigging is to limit movement, rather than to disperse load on the rig point, my takeaway here is anything up to 120 degrees is fair game. Is that your conclusion as well?

 

[Phil]

I’ve seen this. Good stuff. My understanding is at a 90 degree angle it’s roughly 70% of the load on those two points, at 120 degrees roughly 100%, and over 120 degrees you increase past 100%. Since the general purpose of a balancer added to rigging is to limit movement, rather than to disperse load on the rig point, my takeaway here is anything up to 120 degrees is fair game. Is that your conclusion as well?

I am inclined to agree. One key thing I took away from this video is the concept that one can relatively accurately visually estimate angles up to 120 degrees. If you're off by a couple degrees at angles below 120 it's not a big deal. Estimating angles near 150 is much more difficult and the change between 150 and 155 is vastly greater than the change from say 90 to 95.

The load on the rigging line/primary rigging point will only be the weight of the limb and whatever multiplier it sees from the route the rigging line takes to the ground. The load at each anchor of the balancer will be what sees the elevated load from a balancer with very flat angle. I think it would be hard to break gear in good shape even with a flat angle doing a limb balance but it's important to identify the ideal angle range and try to stick within that.

 

[TheTreeSpyder]

This is 100% :
2 legs of support so half of Load upwards lift needed per both legs of support.
Divided by the efficiency of support (cosine of angle/deflection from inline of each support leg) to show line tension needed to support load. The rope doesn't get weaker itself, just less efficient support at angle, just like a table leg, pillar etc.
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All the same repeated lessons in cosine/sine tho in larger context, in these older pics(recycling is easier!):
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120 ÷ 2 = 60 degrees deflection per leg (cosine .5)
So yes .5(cos) ÷ .5(half) x Load = 1x Load
90 ÷ 2 = 45 degrees deflection per leg (cosine .707)
So yes . 71(cos) ÷ .5(half ) x Load = .71 x Load
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And is most predictable to stay at 120 or less spread(60 degrees deflection each leg of support) as long as rope and supports can all take full Load within SWL margins.
Flatter/greater than 120 degrees spread forces escalate very quickly by comparison and can quickly escalate to being upside down/in the red range. It took 60 degrees change to go from 1/2 Load to full load tension on line, but doubles that in next 15 degrees and theoretically approach infinity in the next 15 degrees.....

The anchors also have to be able to take side load too. This is sine X tension = side force.
Or, tangent(table below) X half load = side force.
Cosine is to your support cause(cos), as its
Sine is the also carried sin, distraction from cos.
Wrenching capitalizes on sine rather than cosine, so is bastardization of support theory.
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The reason same numbers over and again is because they are typical benchmarks to know. Tangent is handy too as shortcut.

​

spread	degrees	cosine	sine	tangent​
000​	00​	1.000​	0.000​	0.000​
030​	15​	0.965​	0.258​	0.267​
060​	30​	0.860​	0.500​	0.570​
090​	45​	0.707​	0.707​	1.000​
120​	60​	0.500​	0.860​	1.730​
150​	75​	0.258​	0.965​	3.732​
180​	90​	0.000​	1.000​	infinite/ undefined​

Note also how the cosine and sine scales are mirrors of each other, shown here as matching colors(thus less to know, just to 45 not 90!).
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i use a clock mnemonic i made up for the angles and numbers associated to those angle (thus the less to know, now has mnemonic and in less increments of 6degrees).
It is very accurate to 100ths in first 'month'/5 minutes on clock. Every hash/tic/minute is 6 degrees.
The cosine/sine part for 12-1 covering 0-30 degrees can also b e flipped as above to show the mirror cosine/sine values from 2-3 o'clock of 60-90 degrees. And we know the center point 45degrees is uniquely cosine=sine=0.707(only time cosine=sine). This covers the whole 90degrees as also first season on the clock that was also originally used for an annual calendar also,no used as protractor and calculator for cos/sin.
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i have fuller cosine/sine/tangent and clock table on cos sheet of Capstan Frictions Spreadcheat(link). Another rope angle pic (link)
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This can apply to like a 'Clock Hitch'

Note how flat across this is on trunk, this wrenches tighter grip on tree (sine)
>>in trade for loss of column of support (cosine i think of as 'ColumnSine')
>>note is 6 legs support tho
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Linears like legs of support to carabiner use specifically cosine for support and sine for grip/frictions
Whereas a wonder of arcs are that they use both cosine and sine together for both support and frictions/grip in tension arc. As reverse of masonry arc carrying on all compression as cant carry tension, rope arc carries all tension in reverse flow of same geometry..
In linears support capitalizes on cosine and leverage on sine
>>sweating/swigging a rope is leveraging , thus capitalizes on sine
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Not shown:
If brought next step to some wrap_3 & pull_2
>>would have same effect on support as more grip or column support thru
>>flatter 'teepee' (an ol'Dunlap-ism i believe) giving more grip but less strength
>> 4 legs of support, and another gripping turn on host dedicated to grip anyway!
Thus w/fair teepee would be stronger and grip better than if pull all 3 Turns for carabiner.
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More pointed teepee support lines giving more strength in 4 legs
>>at cost of some grip on host, but that dedicated turn on host (not to carabiner) well makes up for that too. Simple wrap_3 pull_2 with ends as seam w/ fair teepee better than Clock HItch for the Clock Hitch makes choose between support and grip more so, where as wrap_3 pull_2 more likely to lend best of both worlds.
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All these are different facets and usages of same principles, that also extend from these flexible support devices on into rigid supports of rock, wood, metal etc.