To add to Peter's excellent comments: We use one 3 foot tether and one 6 foot tether. There are locking caribiners on the ends, with a spinaker shackle, with beaded lanyard on the D ring (Safety Harness side). The Spinaker Shackle will open under full load. Be cautious of any of the caribiners or shackles binding in D rings or U bolts and opening. We prefer dacron tubular material over nylon--and it is impractical for us to put the jack lines on the middle of the boat--since one walks on the decks--and there are too many obstructions---cabin houses, pilot houses etc on the center of the deck. (at least on our boats--also in the motor sailors, there was almost always a "high" side. We used dacron tubular material, with SS 3/16 wire in the center of the tubing (threaded down the center) This is thing enough wire that it will not roll under the foot and twist an ankle. With the steel wire, there is minimal stretch. We had specific points on a large SS Radar arch structure or backed cleats aft for the Jack lines and a sampson post foreward--little slack on the lines. We also had strong points right at the cabin door on the outside and several points on the side of the cabin. Do not clip onto lifelines or similar wires--stenchon posts are not often strong enough. Jacklines need a stop for shackles at each end. Wichard has an excellent presentation at: http://www.wichard-usa.com/Safety%20Products/Safety%20Products.htm I certainly agree with Peter, and allthough I always carry a very sharp--safety/serrated blade knife, I would have a hard time using it if the boat was moving and I was in the water. There is just too much force--pulling the shackle lanyard works very well. The only turn buckles we used on the deck was the motor cycle. The dinghies were held in place with 2" dacron straps, doubled , sewn with dacron in the center, and multiple 1/4" lashing lines to hold it or other items to the Dad eyes on deck. The reason was in case we had to release the dinghy, it would be easy to cut one strand of the rope and have the rest run free. Hypothermia can occur in what appears to be warm water--also exhaustion may lead to drowning. Scott makes a good point about not being able to breath when in water for some. This makes the strobes, whistles, VHF and EPRIBS (On larger crewed boats the personal locator beacons can be substituted). We have carried personal strobes and whistles on the life jackets and harnesses since the 60's. Hard to imagine that someone would not have these. Stay aboard! Regards, Bob Austin