I've been crew on a couple of boats on open crossings. Of them this is what I liked best an now use on my own boat. Twin lines, both run the entire length of the boat with a positive point of contact in roughly the center of the boat. The ends have integrated loops attached to deck cleats
just as you would a dockline. The point of running them aft is to be clipped in BEFORE you exit the cockpit
. Flat webbing is in my opinion the only option. Round material under foot is bad on flat, stable gound, worse on a rolling boat deck
. We also use two lines on each harness. One is the elastic type, 6' when extended. The second is of much shorter length. It serves two purposes. First, when passing the intermedate point you first attach the spare before unattaching the first. Second, every job I've ever done in heavy seas save one I end up doing on my knees of as low as possible, including moving forward. When I'm working I clip in the shorty. Sound like alot to think of to alot of you I'm sure but consider this. Coming from a climbing back ground, I'm always looking to the worst case senarios. These things I've seen; harnessed foredeck crew being washed down the deck by large waves. Even not going over they came down the deck side with amazing volocity, the intermediate point and short tether minimized this. Also should you find yourself in the water
that second tether could make the difference in getting a purchace on deck or bobbing along until you drown. Oh ya, twist your flat webbing before attaching, helps stop them from "machine-gunning" in high wind
but still lays flat under foot.