On my Oday 31 my exhaust goes under the water when motoring at a fair rate of speed. Usually when we are in a hurry, following seas, everyone is in cockpit. So far it has not been a problem. I hear the bubbles and it shoot out the water when it comes up. The exhaust hose or pipe goes up inside the boat to help eliminate the sea water from siphoning into the engine. Hope it never fails to do that.
I have noticed that when I do push the boat the exhaust water seems to be a little black.
Not sure what causes that.