If it is a recreational vessel with a Horsepower / Capacity rating it has enough foam (in the seats and bow) to float level if swamped. Commercial vessels are not required to do the flotation or be Coast Guard approved but they are not supposed to be sold for recreational use.
Slab, the second picture is what I was referring to, more transverse stringers as well as stringers located on strakes or other load (Lift) generating transitions in the hull. Also you want your decking to connect with the stringers running the main longitudinal run as well as in strategic transverse locations for torsional stresses.