I had a Crestliner that had flappers on the splash well. Idea was to keep returning seas from coming in and filling the well when coming off plane, yet allow any water collected in the well to easily drain out.
If yours are under water, I'd say that you are mighty stern heavy.....like some upper scale bass boats I've seen.
20 years ago ? My boating neighbor almost lost his boat 1 day after launching it in the spring. I go down to the docks & his boat has water coming over the floor boards at the stern. I call him and we just get the boat on the trailer. It was a brand new Trophy boat with a large engine. Boats drains out on the trailer thru that very low scupper next to the drain plug. Zebra Muscles caused the flap to stay open.
Dealer said he was getting lots of flooding and rear of boat underwater calls.
How STUPID can a boat company be ???
That scupper is a drain hole for the cockpit (the area where you stand). It lets any water that splashes in flow back out automatically while you're moving.