thru hub/prop exhaust, or dual exhausts

[Bill55AZ]

I bought an old IMP boat for parts to fix an even older IMP boat, but mostly to get the trailer.
Anyway, it has dual exhausts which go out thru the hull. The only thing stopping water from coming up is the rubber flaps on the transom penetrations. I suppose it is good enough, as the motor runs fine, but is this a good design for an exhaust or not?

[saabster]

most cabin cruiser exhausts are under the water or very near.you can get a swan neck (water trap one way valve)to stop water ingressing too far up the exhaust.so long as the engine is well above water level shouldnt be any probs.

[RMSOSF]

General rule.... the top of the exaust riser inside the boat should be at least 12' - 18" above the water line, if it is, you are fine with your setup.