Jacklines
Well, Gord has pushed my button so I'll give my reasoning. I like nylon webbing left moderately slack and I use a two part tether with a 3 foot and a 6 foot section with locking snaplinks at the ends for security and a snapshackle at the harness end for quick release if necessary. The tethers are tubular webbing and have elastic in them so that they shrink up when not being leaned on. The use of taut wire jacklines is, in my opinion, a bad idea. For a discussion see Brion Toss's book about what he calls lifelines. Brion demonstrates that, when loaded in the center, the load on the ends of a jackline are proportional to the ratio of half the length of the jackline divided by the deflection. If, for example, a 200 pound sailor were to fall and be caught up short by the jackline the load on the sailor could be say 2 or 3 g's or 400 or 600 lbs. On my new (old) boat with a 36 foot jackline and a wire that only deflected 1 foot, the ratio is 18:1 and the force on the anchors is 7200 to 10800. This might be enough to break the wire. It is almost surely enough to damage or break out the anchoring point. If the deflection is even less due to stronger wire the load increases in proportion and little is gained by increasing the wire diameter. A nylon webbing jackline will allow some stretch, decreasing the shock loading but the important thing is to leave some slack so that the end loading is reduced. Even a wire jackline with a 3 foot deflection will reduce the load on the anchors to 2400 to 3600 pounds which should be tolerable. To minimize the distance fallen just use the short 3 foot tether instead of the long 6 foot one. As a support, a jackline with a no-load deflection of 3 feet and a 3 foot tether gives the same support as a taut wire and the 6 foot tether. They will both provide a steadying pull at the same distance, 6 feet. If you fall on a taut, non-stretching jackline both you and the jackline may end up in the drink. By the way, none of the major manufacturer's harnesses have the crotch straps required by the offshore rules. It is relatively easy to come out the bottom of these harnesses. I am having them added to mine.
Well, Gord has pushed my button so I'll give my reasoning. I like nylon webbing left moderately slack and I use a two part tether with a 3 foot and a 6 foot section with locking snaplinks at the ends for security and a snapshackle at the harness end for quick release if necessary. The tethers are tubular webbing and have elastic in them so that they shrink up when not being leaned on. The use of taut wire jacklines is, in my opinion, a bad idea. For a discussion see Brion Toss's book about what he calls lifelines. Brion demonstrates that, when loaded in the center, the load on the ends of a jackline are proportional to the ratio of half the length of the jackline divided by the deflection. If, for example, a 200 pound sailor were to fall and be caught up short by the jackline the load on the sailor could be say 2 or 3 g's or 400 or 600 lbs. On my new (old) boat with a 36 foot jackline and a wire that only deflected 1 foot, the ratio is 18:1 and the force on the anchors is 7200 to 10800. This might be enough to break the wire. It is almost surely enough to damage or break out the anchoring point. If the deflection is even less due to stronger wire the load increases in proportion and little is gained by increasing the wire diameter. A nylon webbing jackline will allow some stretch, decreasing the shock loading but the important thing is to leave some slack so that the end loading is reduced. Even a wire jackline with a 3 foot deflection will reduce the load on the anchors to 2400 to 3600 pounds which should be tolerable. To minimize the distance fallen just use the short 3 foot tether instead of the long 6 foot one. As a support, a jackline with a no-load deflection of 3 feet and a 3 foot tether gives the same support as a taut wire and the 6 foot tether. They will both provide a steadying pull at the same distance, 6 feet. If you fall on a taut, non-stretching jackline both you and the jackline may end up in the drink. By the way, none of the major manufacturer's harnesses have the crotch straps required by the offshore rules. It is relatively easy to come out the bottom of these harnesses. I am having them added to mine.