scupper change from floor to transom

[irish]

I have a 2001 SeaCraft20. I am thinking about adding scuppers above the waterline and above the floor so that water would run out if I got alot of water in the boat. The scuppers I have are self bailing but water does not leave very fast unless one is going forward, which may be tough to do if the boat was in the situation where there was alot of water in the boat. A consideration would be that if there was alot of water in the boat, would the scuppers then be under water and rendered useless? Any thoughts? These would really be emergency scuppers. Thanks for your input.