Seriously, 7 out of 10 in response to a survey in Fine Woodworking categorize Mortis and Tenon as the strongest joint, however Rob's socket is a different animal, I would imagine. I know nothing about what's proper in boat joints, to be quite honest. But it is a socket as Rob mentions, which is what I'm going forward with in my quest for a beam insertion temporary bracket to facilitate "plugging" in and out  full length crossbeam to convert a demountable Proa I'm contemplating in design allowing for a fast mountable crossbeam to be attached while still on a trailer.

Bob