Strongest Block Attachment Sling

southsoundtree

southsoundtree

Been here much more than a while
Location
Olympia, WA
Since negative-blocking down a spar can double the force on the block attachment sling, creating such a large load, I'm wondering what is the strongest thing to use in a 3/4" block.


I (stupidly) knicked my big loopie sling that I had been using. I bought a 3/4" double-braid dead-eye sling, which I really like.

Just curious what people use when they have to go close to maximum.
 
I just bought some 1" double braid polyester (38,000 lbs. ABS) for that same thing. Gonna splice a 10" eye in it for catching wood.
I was using a 7/8's" eye sling for the 3/4" DB rigging line, but feel safer using 1".
Matching the MBS of the rigging line to the MBS of the eye sling isn't safe. The eye sling should be 1 to 2 sizes larger in diameter.
 
My block is a 40000# Minimum Breaking strength--4000 wwl (this gets double the force)
Bigger rope is 1300 wwl
eye sling is 22000 mbs, 2200 safe working load (this gets double the force).
I have a 1"+ marine rope for the porty
different safety factors are used on the different POW's but their recommended safe working load is 2000#.


I believe a rule is that the rope should be the weak link in the system. Perhaps with half-hitches and running bowline's strength reductions and wear on the rope, this may still hold to that rule.

I wonder when people go big with 3/4", 7/8" or 1" ropes?


Seems that Tenex is the strongest sling that I could easily find on Wesspur's site with a swl of 4450#, and a Hobbs 1" block is 8000# swl.

Seems that a block that holds a 1" rope will only handle a 1" sling without forcing outward the sideplates (which I take to be a no-no). This seems like it will still make the sling attaching the block to be the weaker point over the rope since there is the doubling force.
 
[ QUOTE ]
I just bought some 1" double braid polyester (38,000 lbs. ABS) for that same thing. Gonna splice a 10" eye in it for catching wood.
I was using a 7/8's" eye sling for the 3/4" DB rigging line, but feel safer using 1".
Matching the MBS of the rigging line to the MBS of the eye sling isn't safe. The eye sling should be 1 to 2 sizes larger in diameter.


[/ QUOTE ]

I agree Norm. Your anchor should always be the strongest part of your rigging system. I will usually upsize 1 to 2 sizes as well.

I also prefer the double braid slings for my anchors.
 
[ QUOTE ]
I just bought some 1" double braid polyester (38,000 lbs. ABS) for that same thing. Gonna splice a 10" eye in it for catching wood.
I was using a 7/8's" eye sling for the 3/4" DB rigging line, but feel safer using 1".
Matching the MBS of the rigging line to the MBS of the eye sling isn't safe. The eye sling should be 1 to 2 sizes larger in diameter.


[/ QUOTE ]

Norm,

Are you putting it in a 1" capacity block, or are you not concerned about lateral pressure on the cheek plates?

Thanks.
 
Sean, I was just wondering what they have out there for 1" capacity blocks?

I have seen the 1" capacity Hobbs Block and I don't think they get any better than that, but the price isn't cheap.
 
[ QUOTE ]
[ QUOTE ]
I just bought some 1" double braid polyester (38,000 lbs. ABS) for that same thing. Gonna splice a 10" eye in it for catching wood.
I was using a 7/8's" eye sling for the 3/4" DB rigging line, but feel safer using 1".
Matching the MBS of the rigging line to the MBS of the eye sling isn't safe. The eye sling should be 1 to 2 sizes larger in diameter.


[/ QUOTE ]

Norm,

Are you putting it in a 1" capacity block, or are you not concerned about lateral pressure on the cheek plates?

Thanks.

[/ QUOTE ]

I have the CMI RP131 3/4" arborist block. The top bushing will accept a 1" diameter eye sling.
 
[ QUOTE ]
[ QUOTE ]
[ QUOTE ]
I just bought some 1" double braid polyester (38,000 lbs. ABS) for that same thing. Gonna splice a 10" eye in it for catching wood.
I was using a 7/8's" eye sling for the 3/4" DB rigging line, but feel safer using 1".
Matching the MBS of the rigging line to the MBS of the eye sling isn't safe. The eye sling should be 1 to 2 sizes larger in diameter.


[/ QUOTE ]

Norm,

Are you putting it in a 1" capacity block, or are you not concerned about lateral pressure on the cheek plates?

Thanks.

[/ QUOTE ]

I have the CMI RP131 3/4" arborist block. The top bushing will accept a 1" diameter eye sling.

[/ QUOTE ]


Thanks Norm. I suppose that it makes sense that the anchor end of the block would accept larger diameter than the sheave.

Is this spec usually with blocks? I don't think that I've ever seen it. I ended up just buying two 3/4" rope capacity blocks, and knew that the loopie sling and eye sling that I'd bought would fit since they were no larger than 3/4".

How did you know that spec for your CMI block?
 
We have switched to AmSteel for our sling of choice on rigging blocks. Its stronger lighter and smaller in diameter giving us a better bend ratio. I believe were using 1/2" with a tensile strength of 34K
 
[ QUOTE ]
We have switched to AmSteel for our sling of choice on rigging blocks. Its stronger lighter and smaller in diameter giving us a better bend ratio. I believe were using 1/2" with a tensile strength of 34K

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Be aware that Amsteel Blue has almost 0 stretch. That means the <u>tree</u>, lowering line and pulley absorb the added force.
 
[ QUOTE ]
Be aware that Amsteel Blue has almost 0 stretch. That means the <u>tree</u>, lowering line and pulley absorb the added force.

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Since the sling in a lowering scenario absorbs very little energy in the first place (compared to the much longer rigging rope), the choice of sling material should have almost no effect on the maximum forces experienced by the other rigging elements. Even if the sling had exactly zero stretch, and therefore absorbed zero energy, the rest of the system would hardly notice the difference.

Using Amsteel Blue for the rigging rope, on the other hand, would make a big difference. Some part of the system has to be able to absorb energy or the forces get out of hand.
 
Southsound here is a picture from odis when he worked with zeb haney in seattle. I'd like to see the block he uses but this is a dead eye sling of his.
 

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looks like probably 1.5" amsteel. pictures are slightly deceiving because we are only seeing the spliced portion of the rope, so it's about double thickness in that area.

1.5" amsteel has a tensile around 225,000 lbs i believe.
bigeyes.gif
 
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