Staying attached to the boat if you are washed overboard
A jackline is a long rope or wire running the length of a boat (usually a sailboat) from the bow to the cockpit. Its sole purpose is to keep you attached to the boat in bad weather.Clipping the distal end of your harness tether to the jackline allows you to roam the length of the line fore and aft, like a dog in the backyard.Ideally, a jackline would run along the centerline of the boat— then your tether could be short enough to stop your being washed overboard. But there is a mast in the way, and a boom vang, and possibly a dinghy or life raft, and various other gear and impedimenta on the cabintop, so the usual compromise is to set up two jacklines running along the side decks where they join the deckhouse.

Popular positions for jacklines. The lines on the side decks may be snugged closer into the cabin sides, and they may be made of stainless steel wire, Dacron line, webbing, or tubing

When you clip onto jacklines in that position, the tether will be too long to prevent you from going overboard (unless the boat is extremely beamy) and it will be necessary to stop the jacklines about 5 feet short of the stern. Then, if you fall in the water, you will be dragged alongside the boat instead of out of reach behind it.Ideally, you should wear two tethers, one short and one longer—but no more than 6 feet(1.8 m) —so you can move around an obstruction by clipping on the second tether before un-clipping the first.Jacklines must be at least as strong as the safety harness and tethers, and are often made of un-coated stainless steel wire if they can be snugged against the cabin sides. If there is any chance of their rolling underfoot on the side decks, use 1-inch-wide (25 mm) nylon or Dacron webbing instead because it will lie flat. Nylon webbing is more readily available but is not recommended because of its excessive stretch.If you use Dacron rope instead of webbing, make sure you can distinguish it at a glance from the running rigging. It won’t help you much to clip your harness to the spare jibsheet.See also Harnesses.

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