I have no real experience using jacklines, though I have certainly considered them. One thing that has always occurred to me about jack lines is that I see great value in them on the foredeck, but would always be concerned about them being a royal pain from the companionway aft. Either they will be flat along the rail, in which case you can still go overboard on the side you are hooked in to, or they are in the way in the cockpit. We all know that if you go over the edge, it is exceedingly hard to get aboard a moving boat. I would be much more inclined to have the jacklines start at the aft end of the coach roof and go forward, and clip into hard points in the cockpit except when going forward. This would have the extra benefit that the jackline being shorter, it would have less slack. Does this make sense to the rest of you?