Spliced eye slings

[rwilk]

Hello guys (& gals if any),

I'm new to the site and arborculture in general. I have been a silent reader for a few months. This site is great, and I have already learned alot.

Today though I have a need for some help. I have been doing some light rigging and mostly opening dropzone work. I have a large pecan tree that I bid on that will require some medium/ heavy rigging. I need to purchase 2 spliced eye slings, (1 for and anchor point up top and 1 for anchor point to attach the port-a-wrap). My funds, like everyone else, are limited. What would be the most cost effective and multi use length slings. The biggest trees I intend to tackle will be about 38"dbh. Also, what size block/pulley do I need. Will say to lower 6ft sticks of 16-20 wood.

I now have 1/2" 12-strand double braid ropes. 2 I use for climbing only, 2 I use for rigging only. What is a good heavy rigging rope.

I know these are alot of questions in one post, but hey lets get it all at once.

Thanks guys

rwilk

 

[treeclimber165]

I've always liked the $84 block from Sherrill. (#15160) It will hold up to 3/4" rope, weighs 3.5lbs and has a SWL of 4000lbs. I've used them for years and they hold up well. It does everything the fancy expensive painted blocks will do.

For use in the tree, I like the 5/8" CMI pulley attached with a 50Kn steel biner. SWL is 3400lbs and it only weighs 32oz. Sherrill #15221, $54 (pulleys were all on sale last month for 10% off).

For slings, the cheapest alternative is to buy 3/4" Tenex by the foot from a cheap online supplier and splice your own using a locking Brummell splice. Sherrill sells them all made up, but they are pricey considering the cost of materials and the locking Brummell is very easy to make in Tenex.

For a Bull rope, I like the Sampson Stable Braid. The 5/8" has a 16,300lb tensile strength, which is a lot more than most 3/4" ropes. Sherrill has a price match guarantee, and it is available substantially cheaper if you shop around.
I didn't shop and paid $179 for a 150' hank.

 

[rwilk]

Thanks 165

I can't splice my own yet, so I know I'll be spending a little extra. As for by the foot, what is a good length to tie a timber hitch or cow hitch on a 38" DBH tree.

rwilk

 

[treeclimber165]

Here's the NE splicing page, click on the link for 'brummel'.
http://www.neropes.com/splice/default.htm
Sherrill sells the slings 12' and 16'. If you splice your own, the splice will eat up about 1'. I have a 16', which is long enough for most trees around here. I'd prefer a shorter one for in the tree though. I'm going to get some more Tenex also so I can make up a couple more of different lengths. JPS knows a cheap place to get it online.

 

[Kneejerk Bombas]

Twice around a big tree takes a lot of rope. I have a 20 footer that goes once around bigger trees, so I supose you would need 40 or 50 feet.
The rope only needs to be as big as the lowering rope though.
How about one turn on the tree with bigger rope?

 

[treeclimber165]

Originally posted by Mike Maas
Twice around a big tree takes a lot of rope. I have a 20 footer that goes once around bigger trees, so I supose you would need 40 or 50 feet.
The rope only needs to be as big as the lowering rope though.
How about one turn on the tree with bigger rope?

I got the 3/4" Tenex sling for two reasons. It doesn't hold up to wear as well as Stable Braid so I bought a larger size, and it is what my Vermeer guy had in stock. If I were going to order another 16' sling, and pay $48 for it, I'd get the Stable Braid sling. But Tenex is available for $1-$2 per foot and the locking Brummell splice is really easy in Tenex. It is also the same splice Sherrill uses in their slings.

 

[John Paul Sanborn]

For the pulley anchor point I would say a hevy loopy sling, forces on it are 2x the lowering line, but used as a basket you get 4x the swl of a single line (minus the splice).

You can adjust one so that you can do a wrapped basket or girth hitch (choker) which reduces the inheatent weakness of any splce or knot.

I'll let Nick or someone with more resent splicing training give the reduction factor for the loopy splice but 7/16 tenex has a 900# swl on a single leg.

Sherrill has 4 different loopies listed on their web page, up to 2k. If you think you will exceed that then a stable braid sling long enough to ties a cow hitch would be better.

A big loopy or whoopie would be nice, but a long deadeye double braid would be most economical for the PW atatchement. 38 in D has a C of around 10ft so a 14 ft 3/4in eye sling would be able to be timber-hitched to the trunk. Watch out for taper, tie in just over it.

Bailey's rates it's 3/4 SB eye sling at 2040# SWL.

When running a PW you need to remember thet the friction breaking will multiply the loading force to the rope. Dave Spencer, in CN, did some dynomometer tests with his own PW model and found consistant force multipliers of around 3.5 wehn running the load down properly. so if you plan on doing 500# peiceshat is 1750# on the lowering line, doubel that for the anchor lines or 3500#.

I dont have my wood weight table handy but remember 65# for a cubic foot of white oak.

Time for the math police to watch closely

the volume of a cylinder is (pi r sq)h .... so for a 20 in 6 ft piece of white oak

3.14*(10*10)= 314/144 = 2.18*6 = 13*6 = 850.4

Soooo that means you may have loads around 1700 on the line if you go that heavy.

if this is the case, you may want to go to 7/8 stable braid for the lowering line which has a 2900 swl.

1/2 inch is 1000, 7/6-1300, 3/4-2040,

I was using 7/16 for most of my rigging, but have started to go to the 1/2 a lot.

Personaly the few times I rig out any real big stuff I reyly on the 10% SWL as being very conservative and my ropes are one part of my kitty I do not abuse.

 

[Kneejerk Bombas]

Two things John, first how do you go twice around a 10 foot tree and have enough left over to tie knots and hang a port-a-wrap with a 14' rope?
Second, how does the strap at the base of the tree end up taking 3.5 times the force as one leg of the lowering line?
Where's joe when you need him?

 

[treeclimber165]

Originally posted by Mike Maas
Two things John, first how do you go twice around a 10 foot tree and have enough left over to tie knots and hang a port-a-wrap with a 14' rope?

Go once around the tree and tie a timber hitch, not a cow hitch.

Second, how does the strap at the base of the tree end up taking 3.5 times the force as one leg of the lowering line?
Where's joe when you need him?

Good question. But Joe lost me on his last in-depth trigonometry lesson.

 

[Kevin]

I believe the cow hitch is favored over the timber hitch.
The sheave on the block should also match your bull rope.

 

[John Paul Sanborn]

Second, how does the strap at the base of the tree end up taking 3.5 times the force as one leg of the lowering line?

What i ment to say is that friction breaking causes a force multiplyer of around 3.5 on the lowering line. A 500# load put 1700# of force on line when Dave ran his test. That puts 3400 on a pulley that runs the line paralell to it's self.

I cant say if the force on the PW anchor would be around 1.5x the lowering line or what.

 

[Joe]

If Dave Spencer is stating he observed line tensions of around 3.5×'s the load at the anchor point, then his FOS
(friction on site) friction device was connected to his dynamometer which was connected to the anchor sling. If you guys want to get the beginnings of some hard empirical data on drop tests, get the ASPR videos. The late Dr. Peter Donzelli designed the test which was done with the collaboration of Arbormaster Training Inc. The workbook which comes with the video series I believe can be purchased separately and has the #'s in it. There are only a couple of #'s published but whoever reads them will get the point. You should find the #'s JPS is stating is realistic for a load which is run instead of held. This means the rigging point sling will end up with a potential tension of 7×'s the load when the load is gradually stopped.

Joe

 

[Kneejerk Bombas]

What about the loads at the sling holding the brake?

 

[Joe]

Originally posted by Mike Maas
What about the loads at the sling holding the brake?

Hi, Mike;

I'm just using terminology that is supposed to be standard to tree rigging. I learned it from material written by Blair, Arbormaster, S. Lilley, and the various rigging articles in our trade magazines. Rigging point refers to the rigging block in the tree. Anchor point refers to where the friction device is located. The sling is but an extension of the tensions from the work line, so, this means the tension at the eye of the sling will experience the tension extended to it from the friction device. It's common sense correct? I have no hard #'s or explanation about how the tension dissipates through the anchor point sling if this is what you're asking.

Joe

 

[Kneejerk Bombas]

Rigging point/ anchor point, good distinction.
rwilk's original question got me thinking about how big an anchor sling needs to be, after all they are pricey, and any sling long enough to go around large trees need to be custom made.
Let's say I'm rigging with with 1/2" line and I like to use a Clock Hitch(a hitch which requires two turns around the trunk), will a 1/2" rope sling be a proper match?
How about if I use a single wrap and simply attach the port-a-wrap to the eye of the 1/2" sling and tie the end off, as Brian suggested.

 

[John Paul Sanborn]

How about if I use a single wrap and simply attach the port-a-wrap to the eye of the 1/2" sling and tie the end off, as Brian suggested.

If the rope is rated for the operation and you can get five turns on the timber hitch, what is the problem? I do it frequently when skidding logs out and did it with a PW prior to buying The Winch.

The only problem I see with a timber hitch is it's tendancy to creep with multiple cycles. It takes monitoring and retieing. A compitant crew should have no problem doing this.

Looking at your diagram it looks like the clock hitch is a stilson backed up with a timber hitch???

 

[Kneejerk Bombas]

I was asking if a 1/2" sling was a good match for a lowering operation with a 1/2" lowering line, as far as strength is concerned.

And the clock hitch is different than a cow hitch in that with a cow hitch you attach the brake to the eye of the sling. With a Clock Hitch the brake is attached to both ropes going around the tree on the opposite side of the tree of the knots.

That's suposed to be a clove hitch at the end, not a timber hitch. I don't recommend a timber hitch for any tree operations.

 

[John Paul Sanborn]

Gotcha.