... Since you have a bildge with a bildge pump, your bildge is
only "self bailing" for as long as the pump and float switch operates
correectly. I would consider this as part of the "self bailing" feature
of your boat.

Thanks for the clarification. This means I should not consider the
bilge pump as a part of "self bailing".

Why are you backing down so hard that the water is coming in
the boat over the transom? What make boat is this and what
size engine is on it? Where are you running this boat?

No, I have not been backing the boat yet. The boat is still sitting in
the driveway for the rest of this cold winter. I was just mentally
thinking through all the possible situations, such as when someone is
fighting a big fish, and the big fish is pulling almost all the line
from the spool, and I need to back up the boat to recover the fishing
line before the fishing line runs out. Now, I think about this one
more time; I have a feeling that this situation probably will not
happen; the reason is that the person doesn't have to fight the fish
from the stern of the boat; he can simply walk up to the bow and fight
the fish from there; then I can recover the fishing line by moving the
boat forward instead of backward. The situation that I originally
thought would only happen if that person was fighting the fish from a
rear-facing chair; my boat doesn't have such a rear facing chair;
therefore, this situation will never happen.

The only situation that I think I may see water coming through the
transom cut out is when I put the boat in idle and waves start kicking
up, and the fishing is going good that I don't really want to quit.
Now, I think about this. The amount of water probably will not be much
in that situation.

This means I really don't need to build a splashwell at the transom,
and I really don't need to worry about the issue of having a splashwell
that may block the drain holes in the transom that are for
self-bailing.

I would not consider blocking the cutout in the transom,
not a good idea.

Good. This means I can forget about the issue of building a
splashwell, and I can save my time. Thanks.

Jay Chan