The figure eight (8) descender as compared to a rack.
For rappelling the 8 can be configured for low, medium and high friction like a rack but you must plan ahead with the 8 as there is only one way to add friction once the load is in motion. The Rack can be easily adjusted by adding or removing bars or hyper bars on the go, a huge plus.
The 8 as compared to a rack for belaying a descending load. As before, plan ahead with the 8 while the rack is easily adjusted to meet the need.
But now the 8 can excel. Belay a climber with a rack. It is possible, but difficult. If you are in the system, you are working further out from your body which is both harder and requires more clear area. Plus with the rack there is always the risk of dropping the last or only bar. Changing your rappeller from decent to accent is only a mental process.
Material of 8 and bars. Aluminum adds to the friction in both cases but wears faster. No problem with a rack, just replace the worn bar but an 8 must be replaced. In the dirty environment of a cave, forget the aluminum 8. Use only a stainless steel (SS) 8. the cost will be twice as much initially but the SS will out last the aluminum many times. I've seen aluminum 8s, more than one, that has been worn nearly half way through. I couldn't figure out how that was possible if proper rope care was done till one real muddy trip, yikes.
The 8 will cause the rope to twist but this can be worked around and it does no permanent harm as long as the rope can relax or equalize. The Rack imparts no twist. I suspect that some of the twisting is the result of bunching the twists in kernel yarns to the end of the rope.
The 8 can be misconfigured. The Rack can be misconfigured. Ouch, double check every device and every time.
Conclusion, Rappel yourself with rack, but if you are belaying some one else in their decent use a SS 8. Preferably a Rescue 8 as they are heavier and have the ears for easy, secure lock off.
And as a guide, on any rappel, the person rappelling shall use an autoblock. I explain how it works and then have them affix and test the autoblock. Even when they are belayed on a second line. Remember we are training, not caving for ourselves.
If you are dealing with the BSA, SRT is always performed with a second belay line. A fireman's belay is only permissible with doubled ropes. Just the rules. But the fireman's belay puts the belayer at risk and has resulted in several injuries as reported in the Caving Accidents journals
My thoughts and methods. I invite your comments and don't forget to send your suggestions for the merit badge to
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