About 18". The T Docks round plate makes it easy to preset whatever depth you want. I waited to deck the docks until all the posts were set, and the brackets leveled. It's much easier to maneuver everything into place without the added weight of the decking.
I'm not recommending this, but I have a cheap 8' aluminum A frame ladder with 4' long angle iron bolted to each side at the bottom of the legs. It makes it a stable platform to work of off in slightly deeper water.
