Yes, we have these attached to our stationary dock that is attached to our floating dock. As seen in photo.
I fastened them to 2 x 6 Pressure treated wood, double plated so I used 3/8" Galvanized bolts, 3" in length.
Yes, mine to gang planks to go to the floating docks as we have 6 ft. tides twice a day.
No backer plates but I fasted them to a 2 x 6 pressure treated, double plate and used 3/8" galvanized lag bolts 3" long.