Thread: Quick line question...

1. Quick line question...

I think I know the answer, but that can get you into trouble, so I figured this was the perfect place to ask...

Hammock support line strength. It seems I remember the general rule of thumb was you determined the weight limit of the hammock lines by dividing the line strength of the material by a factor of five. So 1600lb strength rope would get you at ~320 pound limit for your hammock (as long as the material of the body would hold up).

Now I'm working a review of a hammock system and the manufacturer told me his line strength was 770 pounds, given my uneducated beer math formula that would mean the load of the hammock lines limit the user weight to 152 pounds, but the manufacturer claims a load limit of 350 pounds.

That said, when I looked up the specs on the rope I thought he was using, it was 1600 pounds. I'm wondering what the disconnect is here.

2. You are talking about safety margins. You need to ask the manufacturer if they factored in a margin and if so what it is. Otherwise assume the number they gave you is tensile and factor in your own margin, just to be safe. But you best bet is to ask the manufacturer.

3 or 5 to 1 is pretty safe. Some folks like a 10:1 which is an OSHA requirement for anything supporting human life. (IIRC)

What rope do you believe the manufacturer is using?

3. Originally Posted by opie
You are talking about safety margins. You need to ask the manufacturer if they factored in a margin and if so what it is. Otherwise assume the number they gave you is tensile and factor in your own margin, just to be safe. But you best bet is to ask the manufacturer.

3 or 5 to 1 is pretty safe. Some folks like a 10:1 which is an OSHA requirement for anything supporting human life. (IIRC)

What rope do you believe the manufacturer is using?
Ahh, but which manufacturer to I ask? The rope manufacturers (ever reference I can find to 6mm rope) advertises ~1600 lbs, which is what I mentioned in my review (see the review of the Hammock Bliss Sky Tent), but Hammock Bliss CRO wrote me and said this is wrong, the rope is rated to 770 lbs. I cannot find a 6mm climbing rope anywhere rated that low. I wonder if this is some sort of inferior rope?

4. Awesome topic! I was actually laing in my hammock night before last and wondering just how much weight my 200 pounds was really exerting on my Whoopie Slings... I figure it has got to be more than 200 since they are rated at 1600, otherwise why go so high with the rating?

So, if I am hanging at the 30 degree angle, how many pounds is being put on the cord?

5. Sounds like the hammock manufacturer is doubling the safety factor. Safest scenerio would be a much higher tensile than listed, a rigging SWL of 1600 (5:1) futher downrated by the hammock manufacturer to 770 (10:1) for human load rating. As others have said, tensile a strength is the estimated breaking load. Working load is determined by purpose and/or industry. Oh, and use trig for your calculations. Ratios kill people if the angles are skimped.

6. Originally Posted by SGT Rock
Ahh, but which manufacturer to I ask? The rope manufacturers (ever reference I can find to 6mm rope) advertises ~1600 lbs, which is what I mentioned in my review (see the review of the Hammock Bliss Sky Tent), but Hammock Bliss CRO wrote me and said this is wrong, the rope is rated to 770 lbs. I cannot find a 6mm climbing rope anywhere rated that low. I wonder if this is some sort of inferior rope?
If the CRO said the rope is rated at 770 pounds, assume this is a tensile figure with no margin factored in.

Imma do some googling real quick.

7. Hard to find a climbing line that size with that rating based on a 10:1. About the best I can find is something around 11mm with a 770 pound WLL based on a 10:1.

That size line and with a 770 pound rating, perhaps its already based on a 5:1.

But since the person you asked stated it has a 770 pound limit, Id wager they dont know what its tensile is. I would ask more questions because a 770 pound limit on a hammock suspension is sketchy.

8. Originally Posted by opie
I would ask more questions because a 770 pound limit on a hammock suspension is sketchy.
That is what I was thinking and I've requested more information from HB.

9. Originally Posted by SticksBlog
Awesome topic! I was actually laing in my hammock night before last and wondering just how much weight my 200 pounds was really exerting on my Whoopie Slings... I figure it has got to be more than 200 since they are rated at 1600, otherwise why go so high with the rating?

So, if I am hanging at the 30 degree angle, how many pounds is being put on the cord?
At 30 degrees you are exerting 200 pounds on each end of your hammock. The steeper the angle the less force, the shallower the angle the more force and the force increases dramatically.

The reason the rating is so high is because that is the smallest diameter Amsteel Blue one can get. Dynaglide is about the smallest diameter line folks use to hang from rated at 1000 pounds and 1.8 mm diameter.

10. I suspect Hammock bliss has a problem. IF they say the rope is rated at 770 we are talking 77 lbs for the hammock pull at 10:1. I'd ask them if they mean it rated at 770lbs with after safety factoring.
I would also want to know if they are assuming equal division of the load between the two ropes.

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