triathjohn, sorry, no pic. Don't overthink it- it's like having a second winch on the back of the trailer with it's rope attached to the bow so when you wind the winch the boat moves toward the winch and off the back of the trailer, except there is no second winch, the winch rope is just diverted, by the snap shackle/block, so it can pull from the opposite direction.
Yes, I use the same winch for either operation. I've only used the system for backing the boat off the trailer once, because the extension has been so easy to use and effective. I backed the boat off the trailer in my back yard so I could work on the centerboard. It worked well with no water there so I assume it will also work well with some water.