The breaking strengths mentioned for the
harnesses and jacklines were interesting. For a 200 lb. man, that means that the
harness, for a 3300 lb. breaking strength, would have to be subjected to 16 g's!! Or 532 ft/ sec sec. I'm not sure at what point those acceleration forces would cause serious musculoskeletal or internal damage, but considering that the webbing of the harnesses is often not more than an inch or two wide, if someone were subjected to those forces, it would put a lot of pressure on the body.
I would be interested to know how the loads, factors of safety and breaking strengths were generated for the harness specifications. And to play devil's advocate, is there a load or acceleration at which one would in fact want the harness and/or jackline to part in order to prevent injury?
The jacklines are specified to be no longer than two (2) meters, or about 6.5 ft. allowing a crew member to move about the vessel and perform his duties. The length limit is probably in place to limit the potential of a large snap loading on the
line, harness, and individual. However, the regulations specify "static"
lines. This typically, e.g. in rock climbing parlance, means that the line does not stretch. This means that all (nearly) of the force is transmitted to the harness and person. Rock climbers use "dynamic" line which has a lot of stretch in it, reducing the acceleration, and hence force, in a fall.
There is a corollary to this in the building and construction trades, namely in OSHA regulations, which require the jackline to be constructed such that it has material built in which acts as a shock absorber and damps out some of the accelerations and force imparted to the worker.
In short, for most conditions, I'm sure the specifications are appropriate, but in the most extreme, is the crew member choosing between potentially thrown overboard or major internal injury / paralysis?