do we need an eye-splices???

S

sorek

Location
Poland
I was just studing the NAA "rigging for removal workbook" and I found there that:
(page 11) loss of strenght due to bends for bowline is 35-40%, which means we use 60-65% of possible strenght.
On the next page of this book I found the info that lashing hitch(timber hitch, cow hitch) reduce 35% of possible strenght of our rope, which means we use up to 65% of possible strenght of our rope.
here is(are) the question(s):
Does useing an eye-splices make any difference??? Does it realy make hole system stronger if we can clearly see that the cow hitch is as week as bowline ?
do you know what I mean? Where is the point in paying for eye-spliced slings`?
Marcin
 
Keep in mind that I'm new to this. It is my understanding that an eye-spliced sling does at least two things that an unspliced length of rope used for a sling doesn't do. One is ease of hardware attachment, instead of tying a knot you can girth hitch (porta wrap) or simply put the loop onto gear (arborist block). Additionally the splice is going to be stronger than a knot at this point in the rigging. The second thing that I believe splices do is to add strength in the portion that is back-spliced, essentially giving you a thicker rope at the point where it exits the half hitch (cow hitch with a better half). So, easier to use and stronger. Hopefully this makes sense (difficult for me to put into words easier with visual aide) and if I'm wrong someone with more knowledge will correct me. /forum/images/graemlins/santa.gif
 
Leif, you are correct. One thing that I have been told repeatedly is that a splice eye will reduce strength by about 10%-15%. They are talking about the cow or timber hitch strength not the attachment point strength. If you do not use a splice you will have 2 knots. Spliced sling is deffinetly the way to go.
 
A properly spliced eye will reduce rope strength approximately 10%. Rigging eyes should be minimum 9" long, so there is more "rope" in the system. Tests have shown that large eyes have a higher breaking strength than small eyes.

We had some tests done about 8 years ago on loops. The rope was New England 3/8" filament dacron (3 strand, 4,400 lb. tensile). We tied 3 into loops using a bowline and spliced 3 into loops. All samples tested were 3 feet long (3' loops). The knotted loops broke around 3,500 lbs. All broke at the "horseshoe" bend in the knot. The spliced loops broke around 10,000 lbs, more than double the strength. All splices broke at the taper. The tensile testing machine was at a local factory. It went up to 150,000 lbs. and had just been certified to be accurate + or - 1%.

Any properly done splice is stronger than a knot.
 
There is something to think about when discussing strength or effeciency loss/gain between splices and knots. It's pretty well accepeted that a proper splice will keep more effeciency in the rope if the eye is pulled. Now, consider how often you would use the eye. In a sling lift situation you do apply the load to the eye. That's where it makes sense to use splices. But when a rope is used to tie off a branch or block for lowering a running bowline/marl setup isolates the rope termination so a splice seems less important.

We're all familiar with the "Take Three Wraps" lowering device. The more friction there is in the system the less the load is on the termination. If enough wraps or marls were made on a lowered branch or block of wood you could theoretically not need to tie the running bowline. The slam-dunk load would be spread along the whole rope.

Take into consideration where your rope termination is in the system when deciding whether you need splices. I'm certainly not suggesting that splices are too expensive or not a good value. It all depends on where they're used. If you're pushing the limits of your system into the red zone, get splices. If you are in the low end of the green zone it might not be worth it. Split tails and lanyard adjusters are green zones for me.
 
Mind that every system is as week as the weekest point. I understand that splice is stronger then knot, but you can only replace the bowline with a splice, you'll neveer replace cow hitch..so even when attaching block to the splice(instead knot) you still use a hitch to attache the hole thing to the tree...and that's where you lose the strenght of your rope..
again: do we realy make the "hole system" stronger by attaching the block to the slice-eye instead a knot (bowline or double fisherman)???
 
[ QUOTE ]
The second thing that I believe splices do is to add strength in the portion that is back-spliced, essentially giving you a thicker rope at the point where it exits the half hitch (cow hitch with a better half). /forum/images/graemlins/santa.gif

[/ QUOTE ]

look's like you're the only one who understand my question, I think you're wright, thanks
Marcin
 
Marcin,

I think that your question was answered in many ways. Directly, is your system stronger with a splice to attach the block?- yes. That is to say that all parts are equal for either technique.

Look at it like this, if you use the eye splice your loss of efficiency will be about 10% or so ( at the attachment point).

If you use a bowline, you will lower your efficiency by 40% or so. And considering that the block will see twice the load (180* loading factor) that is quite substantial.

The biggest reason for many to use a splice here is the ease of use- Especially if you're using a spring-lock block and want to disconnect the block each time you tie it.
 
This is a good question to present to our rope manufacturers. Arbormaster has been working with Samson on identifying the breaking characteristics of various rigging scenarios. Is the 'block to splice to cow hitch' one of them? Do they have any info for us?

The other point to consider is do you have the best system in place if things were to go south real fast? If something bad enough were to happen you could have to defend your decisions in court against some greasy, kniving lawyer.
 
[ QUOTE ]
Marcin,
if you use the eye splice your loss of efficiency will be about 10% or so ( at the attachment point).


[/ QUOTE ]
Mark
Thanks for explenation.
Do I understend you wright? If I use a splice to attache the block, loss of efficiency at the attachment point (cow hitch with better half) will be 10 instead 35%? I don't know too much about these forcess but just by looking at this...does s splice have so much to do with affecting the loss of strengh
[ QUOTE ]
(at the attachment point).

[/ QUOTE ]
Thanks
Marcin
 
[ QUOTE ]
Arbormaster has been working with Samson on identifying the breaking characteristics of various rigging scenarios. Is the 'block to splice to cow hitch' one of them? Do they have any info for us?


[/ QUOTE ]
That's a good question as well,
I'd like to see some resolts, how about..block to double fischerman to cow hitch against block to splice to cow hitch...what if they'd told us that those two systems have the same strenght, would splicer's income rapidly drop down?
Marcin
 
sorek- A splice has very little to do with weakening the system. The splice is the BEST way to terminate a rope, especially when strength is of concern.

You'll lose strength when you tie the cow/stilson hitch, but strength loss from the splice is of minor concern.

love
nick the splicer!
 
[ QUOTE ]
but strength loss from the splice is of minor concern.

[/ QUOTE ]
Carpal Tunnel -- How do you know? I've read that it's very symilar to the strength loss on cow hitch.
Marcin
 
Strength loss from a great splice approaches zero percent, but let's call it 10-15%, just to be safe. A cow/girth hitch loses considerably more than that- around 25%, depending on which source you're quoting.

If strength is of any concern, use a splice.

love
nick
 
[ QUOTE ]
Strength loss from a great splice approaches zero percent, but let's call it 10-15%, just to be safe. A cow/girth hitch loses considerably more than that- around 25%, depending on which source you're quoting.

[/ QUOTE ]

So you agree that the weekest point in block+splice+cow/girth hitch system is the cow/girth hitch?
Where would you place the weekest point in block+bowline+cow/girth hitch? Please, mind the fact that (acording to my sources) bowline couses about the same strenght loss that the cow hitch.

Marcin
 
The bowline would be the weak point.

Just use a splice and don't worry about it. I've been accused of using splices in places where they might not be appopriate or necessary (throwlines and friction hitches) but you would be hard pressed to find someone here at treebuzz that would support using a bowline over a splice for the heavy rigging we're talking about here.

Are you trying to get at something here?

love
nick
 
Marcin,

I think that we are talking about the same thing, but going in circles a bit.

[ QUOTE ]
So you agree that the weekest point in block+splice+cow/girth hitch system is the cow/girth hitch?

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Absolutely, if all parts are rated equallly. If you have a block (20K tensile), sling w/ splice (20K tensile), they are near equals. If you tie the sling to something, the hitch has to lessen the efficiency. The only way around that would be a frictionless hitch or using in the basket position.

For tree removal purposes, the cow hitch would be the preferred technique for me. Yes it would weaken the system (sort a) but it that can be accounted for and compensated for. The block and sling should be the strongest point in the system (barring the tree itself).

Does that sound clear and correct or does someone disagree or not follow my thought?
 
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