The military and its loyal veterans have many websites devoted to life in the various branches. The site FoxtrotAlpha has a page about riding the high line between two large ships. The high line usually is used strictly to transfer goods and materiel during replenishment-at-sea operations. It is a rough ride and can be very dangerous. Even so, in a pinch, personnel can be transferred by this method.
Best of all, this page includes footage of Jack riding the high line between the USS Knox (FF-1052) and the USS Cochrane (DDG-21) in “Murder – Eyes Only” (Season 8). You can really see that Jack grew up on the high seas. He makes his way on those ships with incredible ease.
Here’s a video showing refueling at sea, from the USNS Guadalupe (T-AO-200) to the USS Momsen (DDG-92). It gives complete coverage of how the process is begun, as well as implemented. https://www.youtube.com/watch?v=sAlATn4xm4I