You are incorrect. A boat such as pictured is not "sunk" but is swamped. A Boston Whaler will refloat itself. That is right, the small Whaler will come back on top--this FACT-- is one of the reasons that that are called unsinkable and which differentiates a BW and a few other select brands from the chaff.
Let's go over this again, a Boston Whaler, as long as it does not flip, has sufficient inherent buoyancy in the foam filled DOUBLE hull (to the gunwale cap) to refloat, as well, an outboard engine will continue to run even if the boat is swamped (flooded) and powering the boat in forward gear will allow the water to bail over the transom cutout and through the scuppers. I know this because I have done it in both my previous Montauk and our current Outrage. Once each was enough however, rather not test fate.
Yep, that is right, a small Boston Whaler, you can pull the plug, you can turn a dozen hoses into it full on and it will not go down and the water will empty from it. They have no bilge or only a small bilge for water to collect. The hull is a one piece construction of a double hull with foam completely filling it to the gunwale cap. The cockpit depth, transom cutout and scuppers make it impossible to put more water (weight) in the BW than there is positive buoyancy. Sure, if you fill it with concrete and tungsten bar it will sink. Under normal circumstances there is no way to have more water weight in the Whaler hull than there is buoyancy to offset it and therefore it will refloat itself, first spilling over the gunwales, then the transom and then the scuppers.
As to design of the transom, you are once again incorrect. There are two design philosophies for small boats:
1. Design to keep water out with high sides and transom and use pumps to clear the bilges. Water comes in, it must be pumped out. The Titanic Philosophy.
2. Design to let water out using lower sides, relieved transom and scupper, no bilge. Water comes in, gravity removes it. A notched transom on a small Whaler is a positive, not a negative as are the purposely low(er) freeboard/sides. The Surfboard Philosophy and you might know, you cannot sink a surfboard and yet they have no transom or sides at all.