Can anyone tell me what the name of the joint is for the joint that holds the deck and the hull together?

Shoebox?

The joint between the hull and deck does not hold the two together. It is called a "shoebox" style joint as has already been stated though. There are various means used to hold the two halves together. Many lower end / production boats simply use stainless steel wood screws or even rivets. The next step up is generally stainless steel machine screws with Nyloc nuts. (This solves the problem of the wood screws backing out after a hard day on the lake.) The best method is to tab the two halves together with mat and resin. This method effectively makes the two independent halves into one whole unit - which is much stronger.

the ''joint'' molding is mostly there just for the look and finish, in fact.

beside the tabs,,we used a bunch of wood wedges and opened the joint a bit and squeezed in my favorite 5200.lets just say,the deck is never coming off our boats.