Done it once - I assume that everybody knowws to bring your own bread and wine ( chipped glasses and crocks provided with seafood platters).
Don't go to Stone - go up the Mersea Quarters as far as you dare and grab a buoy. Leave the Packing Shed to starboard. In the summer the water taxi comes out for you but I expect he's stopped by then.
Last time I said to him "are we OK on this buoy" he said well it happens to be mine but you can have it for a few quid. I think he says that to anyone who asks! Moral - don't ask