Some years ago,
we practiced trying to get back aboard my boat by yourself in good weather, during daylight, in the Chesapeake. If you trail a warp, you may be able to grab it and pull yourself back to the boat -- if the boat is not moving. If it is moving, it is just about impossible to do. If you went overboard and were tethered to a harness and the boat, you were going to drown unless you could get the carabiner open fast or had a sharp knife at hand. We thought that the best way to use a tether was to use a very short one that would keep you aboard no matter what. Also, getting a boarding ladder down while looking up at it from the water is doable, but as Fred notes, keep your head out of the way. We also tried inflating an inflatable PFD waistpack that requires treading water and then getting it over your head and then strapping it around your chest. Also doable, but it's got to be calm waters and you've got to be a pretty good swimmer/water treader. In the end, we thought that if you were alone and fell overboard with the boat moving and it didn't come up wind and stop (cause you had the wheel/tiller locked or on autopilot), you were not going to get back aboard that boat as the boat is going to Bermuda without you. Best to focus on the basic idea of how to prevent going overboard in the first place.