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  1. #1
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    Safe Working Load Limit?

    Noob at hammock camping. Not so noob at using cordage in the outdoors. Hunting, fishing, camping, wilderness canoeing in bear country, and 30 plus years in the Armed Forces, I have used my fair share of cordage to set up shelters, secure loads, etc.

    Looking at all the stuff here about whoopies, UCRs, ridgelines, etc. of course what gets mentioned is the ever-present Amsteel Blue, as well as Dynaglide and Zing-it et al. My problem is, all that gets mentioned, and often all one can find is the 1000lb, 1600lb....."Breaking Strength". All that is is "Tensile Strength" - put it in a machine - stretch it till it breaks, take an average of a number of tests and you got your number. No knots, no bouncing, no G-forces. I gotta tell ya, I could give a hoot what the tensile strength is, I want to know Safe Working Load Limit (Some manufacturers include this). This tells you what amount of weight it is safe to attach this cordage to. In some types of cordage this can under 10% of the tensile strength. Materials and method of construction being key factors here.

    I have hanks of the ubiquitous 550 paracord that all state 550 tensile. Some have as little as 33lb SWLL and the highest is 115lb. Utility cordage from the same manufacturer, same size, same construction, different materials - tensiles are not as far apart as the SWLL as fractions of each other - weaker cordage has 2/3 the tensile and 1/3 the SWLL of the stronger.

    So, pardon my rant, and since most everyone here is trusting one or more of these to keep their butts off the ground, I am sure they are more than adequate, satisfy my curiosity will ya? What is the SWLL of these various cordages?

  2. #2
    all secure in sector 7 Shug's Avatar
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    1600 pounds for 7/64 amsteel according to whoopee sling site......http://shop.whoopieslings.com/Whoopie-Slings-AWS.htm
    I have been using them for years with no breaking and I have stressed mine. You can see me hitting mine pretty hard at 1:20 in the video below.
    Carry forth
    Shug

    Whooooo Buddy)))) All Secure in Sector Seven

  3. #3
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    You really do want the tensile strength because everything else is a derating from that number. To start with a 10:1 safety factor takes a 1000 line to 100 lbs. Slice it and get 80% of that puts your working load at 80 lbs. Knot it and lose 50% and you have 50 lb safe working. There is a wide range of derating numbers depending on the knot and the material in the line.

    10:1 is a generally accepted ratio for life support hardware. A lot of folks here use 5:1 or 3:1 assuming a 2 ft fall will not kill them. Many of us find that less than reasonable. Bottom line is that is why we all look at tensile strength and go from there.
    YMMV

    HYOH

    Free advice worth what you paid for it. ;-)

  4. #4
    Senior Member DemostiX's Avatar
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    There's plenty here; and I've annoyed many enough to not repeat, unnecessarily, as you can find long threads on this topic. One cord given lots of love was / is Dynaglide, with a putative BS of 1000lb. A (too) tautly hung hammock with a 200 lb er in it would have a BS / load ratio of less than 3. BS to SWLL ratios are never less than 5.

    Others' comments about SWL and safety margins as a function of the base breaking strength are exactly to the point.

    And, to comment on one concern not yet responded to. Hmmking is regarded here as strictly static loading, in mountaineering, rescue, spelunking, or arborist parlance. So, yes, the energy absorption and resilience of this lightweight UHMWPE cordage is small, and it would snap long before polyester cordage of the same BS would if subjected to dynamic loads, such as from jumping. (But, on the other hand, the nylon hammock it is attached to would stretch and reduce some of the transient shock....a little.)

    OP would be right, though, that repeating the breaking strength figure from a vendor, when the MFG and Cordage Institute describe minimal BS-loss from correct splicing, does not address OP's challenge.

  5. #5
    Senior Member XTrekker's Avatar
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    Quote Originally Posted by APRock View Post
    I gotta tell ya, I could give a hoot what the tensile strength is, I want to know Safe Working Load Limit (Some manufacturers include this). This tells you what amount of weight it is safe to attach this cordage to. In some types of cordage this can under 10% of the tensile strength. Materials and method of construction being key factors here.
    Safe working load is often a 10:1 Ratio for climbing or safety harnesses. 5:1 Ratio is what alot of the hammocking community goes by for working load because we dont plan to be falling 5'-10' and needing our suspension to catch us. So basicly you just need to take whatever the breaking strength or tensile strength is of the rope and divide by 5 or if you're going for super safe suspension then divide by 10. Yes knots do reduce strength of some ropes like Amsteel or Dynaglide but actually act in the opposite manner in ropes made out of nylon in certain scenarios. When it comes to Amsteel, learning to splice is your best bet.

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    Quoting from Samsons Rope Inspection and Retirement Guide:

    "WORKING LOADS: Working loads are the loads that a rope is subjected to in everyday activity. They are normally expressed as a percentage of new rope strength and should not exceed 20%. A point to remember is that a rope may be severely overloaded or shock loaded in use without breaking. However, damage and strength loss may have occurred without any visible indication. The next time the rope is used under normal working loads the acquired weakness can cause it to break. Do not blame the rope, it was simply overloaded and failed from what is known as fatigue.

    Going by this I would say the 7/64 Amsteel Blue would have a SWLL somewhere between 280 and 320 pounds.

    Since I got grandkids that won't know any better and do dumb things, and we "adults" who should know better and do stupid things anyway, I think I'll jump up to the 1/8 inch just for a little more peace of mind...

    Never been a "Gram counter" anyway. If it fits in the pack and serves me well, I'll hump it into the bush and back out.

  7. #7
    Senior Member XTrekker's Avatar
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    Quote Originally Posted by APRock View Post
    Quoting from Samsons Rope Inspection and Retirement Guide:

    "WORKING LOADS: Working loads are the loads that a rope is subjected to in everyday activity. They are normally expressed as a percentage of new rope strength and should not exceed 20%. A point to remember is that a rope may be severely overloaded or shock loaded in use without breaking. However, damage and strength loss may have occurred without any visible indication. The next time the rope is used under normal working loads the acquired weakness can cause it to break. Do not blame the rope, it was simply overloaded and failed from what is known as fatigue.

    Going by this I would say the 7/64 Amsteel Blue would have a SWLL somewhere between 280 and 320 pounds.
    Kinda answered your own question I guess.

    Since I got grandkids that won't know any better and do dumb things, and we "adults" who should know better and do stupid things anyway, I think I'll jump up to the 1/8 inch just for a little more peace of mind...
    Not sure if you're referring to "stupid things" as using smaller diameter Amsteel or Dynaglide than what you deem is appropriate for a hammock suspension, as being stupid; but some of us have been hanging from rope a small as 2mm for quite awhile. Sgt. Rock did a great video showing how he makes his UCRs which are made of 2mm Dynaglide and he has been using them for quite awhile with no issues. I just started using Dynaglide recently too and haven't had any issues yet. I think the hammock fabric will rip before the rope snaps anyway. I understand, completely, when it comes to your kids and grandkids and wanting them to be as safe as possible. Use whatever size of rope you feel comfortable with. We all have different opinions on what works for us and we try to respect each others opinions on what works for them.

    Never been a "Gram counter" anyway. If it fits in the pack and serves me well, I'll hump it into the bush and back out.
    HYOH

  8. #8
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    Quote Originally Posted by XTrekker View Post
    Not sure if you're referring to "stupid things" as using smaller diameter Amsteel or Dynaglide [I]than what you deem is appropriate for a hammock suspension
    No, no, nope. Use what ever line you like. I rarely disparage anyones choices especially when they been doing something a lot longer than me! However; have you ever watched Youtube "FAIL" videos? I can just see, well, at least one "buddy" of mine getting half popped and trying to see just how high he could get someone to swing in that hammock and then jumping on himself...

  9. #9
    Senior Member Knotty's Avatar
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    While 7/64" Amsteel has a proven record in the hammock world, one can't fault you for going with 1/8". That's a big jump in strength for not a lot of additional weight.
    Knotty
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  10. #10
    Senior Member oldgringo's Avatar
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    Quote Originally Posted by APRock View Post
    No, no, nope. Use what ever line you like. I rarely disparage anyones choices especially when they been doing something a lot longer than me! However; have you ever watched Youtube "FAIL" videos? I can just see, well, at least one "buddy" of mine getting half popped and trying to see just how high he could get someone to swing in that hammock and then jumping on himself...
    You're beginning to sound like a lawyer.

    Maybe you should be looking at 2 sets of numbers: one, for yourself, using a modicum of common sense, the second for stoopid.
    Dave

    "Loneliness is the poverty of self; solitude is the richness of self."~~~May Sarton

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