i installed one on my oday 20
i also removed the small bulkhead and pulled myself into the transom area to install a plywood backing. i backed used smaller pieces of plywood about 4-6 inches across. i wanted a single larger piece, but due to the curve of the transom it would not sit flat against the stern. i was afraid if i used one piece it would loosen up as the plywood warped to the shape of the transom and i didn't want to have to keep crawling back there to retighten the bolts. i used stainless steel bolts with flat washers and lock washers. i also had to make a couple of disk shaped wedges out of oak so that the ladder attachment plates would sit square on the transom. due to the transom curve it turned out to be alot more work than i expected, but then what doesn't?i think it came out pretty good, although i just put the boat in the water and haven't actually climbed up it yet. i included a link for the ladder i installed.