i'm sorry if i s-lightly abused the terminology; but don't think i'm the first to do so in this way. SWL (to me) is both a ratio, and a highest load acceptable at that ratio. Different manufacturers, industries and situations; use different ratios; just matching the SWL of a krab and a pulley doesn't necessarily mean their strengths are matched if the calculated SWL ratios are different. We have also spoken of the SWL of a system before; if the weakest link is the line, and we set it as a 2/1; then the SWL of the system changes (though not strictly the line component).
This SWL of a system then could be a given force rating that is safest at an agreed on ratio for dragging or lifting etc. Or, at a given load; the ratio to the tensile; or in other words a measure of the fault tolerance; that SWL is about anyway? If this ratio is 4:1; that SWL might be okay for dragging; but you might stop the procedure if that system was to be used for overhead lifting etc.
Perhaps a little tib lysdexic; but all to the same end; a ratio margin of safety/ fault tolerance to a given loading etc. In dynamic components like rope, under dynamic conditions; this higher tensile to load/ higher SWL ratio gives less elasticity. The elasticity depends on line materials, construction, length taking the hit(which somewhat counter-intuitively includes line length to 1st hitching on Load; so extending this is a way to squeak more elasticity in/ not more shock if still before the CG) and percentage of tensile used as multipliers. So, as the safety ratio/ fault tolerance goes up (less load to tensile) the elasticity/ dampening reciprocally comes down.
This is also true of 2/1's etc. What i meant about the elasticity with them; is that adding more line to extend control end gives more elasticity; while using the same addition of line for more supports to the load decreases elasticity; as a flip side to 2 different ways to add line length(like if only had 100' of line to use, adding it as legs to load decreases elasticity; while using it in system other ways increases elasticity). But, adding more length to the 2/1 legs will help mediate that, yes. Please note, a 2/1 drop in elasticity is not just neatly 1/2 loading on support/pulley. i think
For potential static load on support for both these scenarios; Load + Load/legs to load is fair. So, a 1:1 gives 2x loading at support, but that drops to 1.5x for a 2:1 and 1.333_ for a 3:1 etc. So, we could feel safer with a higher power system to the same load. But, in a dynamic loading; the more legs to load reduce the elasticity, thereby increase the potential loading on a drop, but (same 2/1 system) decreases loading on a static hang.
Enclosed is a chart maid years back with the Rigging Calculator. The calculator is not something you take to a job, but rather sit at home and find patterns to make judgemeant calls later with i think. It has 3 different categories: Line length as variable, Height of CG as variable and Load per leg as variable respectively; to sift these same patterns out of/ confirming deeper correct paths, and perhaps showing fault to other thoughts? Also, the StableBraid / Yellow is most extensive tested; showing how same materials and braid; just set to different tensile strength/ diameter varies things.
In DdRT we have a 2/1(less friction) over our own selves(in this folding force back on it's self scenario, to contain closed force system); but at a loss of elasticity/ shock dampening. All the rope lessons have consequence on climbing (and vice versa) too.
Edit: Tom; in single use, eye spliced devices, perhaps 'software' tensile should equal hardware tensile(?). But in repetitive use devices shouldn't the wearable software have higher ceiling, to allow it to drop/wear in to closer to matched components over useful life? Also, in an open system of rigging, 'room' left for a knot decreasing a line's remaining tensile to closer match krab etc.? Pulley and pulley attatchmeant devices as higher rated, but other single leg of loading hardware; could be rated less than line; to allow line to match after wear and knots.
Smaller Version of Attatchment: