Thanks Essman for your info.
I agree with your comments/concern about exhaust backpressure as a result of discharging 2' below the water line. I just can't imagine why a 2 inch dia. thru-hull would be installed there (and capped) with a hatch in the floor directly above if it wasn't used for the exhaust originally?
The '76 Irwin has 2 steps down to the aft hall from the main salon. To discharge the exhaust below that hall floor (with minimum clearance), the thru-hull has to be located 2' below W/L. Discharge at W/L inherantly introduces an other loop with water in it all the time.
Correct me, but I think the newer Iwrin (i.e. 83s) were beamier ~ 13' (much nicer boat too!), and therefore had a lot more room in the engine compartment to accomodate the muffler on the port side of the engine? The '76 has a 11.5' beam and no room for muffler on port side, hence the double cross over. I was tempted to reroute the discharge to sterm, but seem to be stuck with having to go below the floor which means a wet loop below the floor if I want to discharge at W/L. Only other option (unless I hear differently) is to discharge well below the waterline? I've considered discharging midship on starboard side at W/L, but am unsure how to get through the galley or aft washroom with reasonable estetics. Has anyone tried that?