Chains

I respectfully disagree with this. Here is why. The specialized carriers and rigging association are the group responsible for helping the FMCSA create the cargo securement rules.

This chart shows a sling rated at 500 pounds. When used as a single leg sling (a direct securement) it is still only able to lift 500 pounds safely.

When used as a basket sling (an upside down indirect securement) it is rated to safely lift 1000 pounds.

Thoughts?

I believe I have tried to make this point to @TripleSix before but I think I explained it better this time.

 

The reason the FMCSA determined a direct tie down gets 100% is because it pulls down on the cargo effectively making it heavier. The explain it somewhere if I can find it.

 

Did you mean indirect gets 100%? Because direct only gets 50%wll.

Depending on how a tie down is angled a direct tie down can provide 100 percent downward pressure (think shipping container with a chain running from the top corner hole straight down the side) and an indirect can provide absolutely 0 downward pressure. (Same shipping container with a chain ran through both front bottoms holes and stretched way back on each side. )

 

Yes I got them backwards and I'm aware of that but tell the government

 

I'm not talking about in terms of legally. I mean to say, that if you have a 6600 pound chain, hooked in direct securement to an attachment point that is only rated for 5000 pounds, your attachment point is your weak point, not your chain. So I suppose that this means nothing in terms of legal securement, but if you are aiming for that 50% securement, and your attachment points are your weak point, you are not safely secured.

 

I think you actually agree with me. If the WLL of a chain is 500, then direct securement, which is the same as a single leg sling, you get 500. When used the same way (just upside down) in trucking, you only get 250. This means that the way we calculate WLL in trucking is based on a legal concept, and not on physics.

Again, my thoughts are that this is why they only require 50% securement. It's really 100%, but they do the math a little funny.

 

But that's not what you said,

Using your example you have a 6600# chain and binder hooked to a 4000# attachment point that point is still capable of holding 4000# so how do you come up with 2000#?

 

I'm not phrasing things very well. I was, in spite of the fact that the FMCSA does not discuss the ratings of attachment points, still using their funky math.

Let me simplify it. When calculating how much securement you have, you should apply the same standards to the attachment points that you do to the chains and binders. If you are halving everything and going for that 50% standard, you should be halving the ratings of the securement points. I know legally you don't have to, but for the sake of reality and physics, it is something to be considered.

If you have a 6600 lb wll chain attached to a 5000 lb wll attachment point, that attachment point is the weak link in your securement.

 

The reason Indirect is 100% and Direct is 50% is that the FMCSA is lazy and thought it was too difficult to make the regulations worthwhile, so they went with a dumbed down "good enough" version.

In the real world an indirect tie down is one that increases the friction between the cargo and deck, that's pretty much the same as the reg, but the regs leave some very dangerous holes. With an indirect tiedown you can calculate its actual WLL by measuring the angle between the deck and tiedown. Take the sine, multiply by the WLL and there you have it.

As an example, with a load of wood that comes all the way to the edge of the deck the straps are 90 degrees to the deck. Sin 90=1 so you get the full WLL. The regs act like all indirect tiedowns are 90 degrees. With a load of steel the angles can be as low as 40 degrees sin 40=.6427 so now you have a tiedown that is only 65% effective getting calculated at 100% But that's OK, because low loads are steel, and everybody uses steel on steel, and nobody uses snap binders correctly. More people are using straps and ratchet binders on low loads, so regulation no longer works.

Direct tiedowns being 50% is an average. In the real world they provide direct resistance against the movement of the cargo, generally in three directions. You can figure out the real world WLL with the Sine of the effective angle, problem is you have three of them. Easiest way is to measure the opposite leg and divide by the hypotenuse. The hypotenuse is the length of the chain between the attachment points, the opposite legs are the distance fore/aft, side to side and vertical depending on what WLL you are calculating.

Since direct tiedowns split securement in three directions, (vertical, side to side and front/back) you might only have 30% preventing the cargo from going forward, however the regulation depended on the use of G70, since it's WLL is relatively low you will need multiple sets of chains and they will be at a different angle, generally everything averages out to 50%. Then you throw G100 into the mix, it's problem is that it is so good that the regulation can't handle it. Take an excavator on an RGN, hook a pair of chains on the track and go to the other side of the trailer to hook up, it's not uncommon to see chains hooked like that, but only go back 2-3 feet. 3/8.5=.35 so that set of chains only has a 35% WLL. With G100 you might be able to get away with just those two chains, with G70 you will need a second pair of chains that will probably have a lot less side to side securement, but provide more like 70% WLL against forward movement and average out to 50%.

G100 is an amazing product that is well suited to being used as a tiedown (except for the price) but the regs can put it into situations that it just isn't capable of handling.

 

Good info here inside this thread. Found some of the discussion helpful answering a WLL question or two.