The magic of 7/64" amsteel...

[DrPhun]

“Scuba tanks are tested (in not america) for twice their pressure limit (nb, not until they explode) and that is quite arbitrary from a perspective.“

It is more complicated than that. Tanks are periodically tested to 2x, but they are designed to withstand much more, probably 4x, and tested to that at the factory. When I designed hydraulics, they were tested to 2x and designed to 4x.

For these lines, the weight rating is where it is designed to break with a static load. I looked up the specification for 500lb paracord and it requires it to withstand 90% of 500lb when tested at the factory i.e. if it breaks at over 450lbs, it passes. As soon as it leaves the factory, it degrades due to wear, up, knots, moisture, etc. Dynamic loads are multiples of static loads.

And then a business needs to add an extra safety margin because some customers will abuse your product and then complain when it fails. That is why making your own gear is so satisfying - you can make it to your needs and if it starts to wear prematurely, the next iteration will be better.

(I confess that I have made a suspension with dynaglide as an experiment and have not had a problem.)

[S.rider]

From the information on the linked UHMWPE cord on Amazon

The factor of 5 between WLL and Tensile strength is consistent. The sellers of the cordage recommend it.


"Working Load Limit (WLL) = 20% of Tensile Strength, for the longevity of the cord and safe uses

Tensile Strength

Also known as the labeled strength, is the average testing strength at which the new and unused cord would break when tested in laboratory condition in accordance with Cordage Institute Standard Test Methods. The load, applied in parallel to the cord, slowly increases until the cord breaks.

Working Load Limit (WLL)

In practical uses, various factors would impact or reduce the strength of any rope/cord, including knots in the rope, abrasion, humidity, UV, former use and care, etc. To assure safe uses, it's indispensable to adopt a safety margin in the cord/rope strength, which leads to Working Load Limit (WLL).

The Working Load Limit (WLL) is determined by dividing the tensile strength by a safety factor. To assure the longevity of the cord and maintain a comfortable margin for safe uses, a 5:1 safety factor (20% of the tensile strength) is adopted and recommended for emma kites UHMWPE cord for general applications."

iirc, climbers use a 10 :1 ( or 10% of tensile) ratio because of very dynamic loads potentially.

HYOH, and calculate your own dynamic weight and forces sums!

[jeff-oh]

Late to this party, but I do find it interesting that someone new to the forum is so quick to dis-miss the knowledge and wisdom of the long timers. Given this person may not know the level of experience of Grappler, cmoulder, Tom, nanok and all of the others. Guess what I find is interesting is the assumption that after 20 years of active hammock innovation here, this would be a brand new idea never though of. SilvrSurfr showed the history and it still was not believed.

That is fine. He will go out and either learn it works for him or it does not.

[cmoulder]

One good thing about hanging is that unless a brick wall or a concrete column or a dead tree falls on us, it really is very unlikely that serious injury will result from experimenting at 'normal' hang heights.

[Mr. Jowee]

Since we’re on the subject, I once picked up a 1,000lb class F test weight with a 7/64 AmSteel dog bone. Nothing broke, so there you go. Class F weights are used for calibrating commercial and industrial scales.