That is a relatively easy question to answer.. Most folks that use jacklines do not keep them short.. They run the length of the boat from stem to stern. They measure the tether by the length to stand up and move around. So your in the middle of the two tie points for the JackLine. You step back and reach the end of your tether, then you step back again and the JackLine starts to stretch. You continue stepping back till you have the JackLine taught. On a 20 foot JackLine there can be 3-4 feet maybe more from where the line the JackLine started add another 6 feet for the average tether and your off the boat. How many boats do you know are 20 feet wide? And that is if the JackLine is run down the middle of the boat.why his tether didn't keep him on board
You need to use jack lines that do not stretch and tethers that are short enough to keep you inside the lines when you put your weight agains the JackLine and tether. For me I run a single JackLine down the middle of the boat (11 feet beam) from cockpit to mast tied off and stretched tight, then another line on the centerline to the 2feet short of the bow. The tether is 4.5 foot long for the cockpit to the mast and the bow tether 3.5 feet long. When I lean back against the tether it holds me at the boats edge. Sure it is a pain when hooking the bow tether on then releasing the main tether to. Go to the bow, but it is secure and it is designed to keep me on the boat while solo.
So far so good.
I suspect on the race boat the tethers and jacklines are set for speed and convenience of the crew. They may be reviewing their setup in the future.