safer to have dry exhaust preferably stainless 321 or 430
for its heat resistance with the correct pyro wrap and fire
containment blanket suited for the temperature.
Keep it simple.
Ask the turbine boat owners who do have water cooled exhaust
what happens when the big 140lb DC electric motor fails
that operates the water flow to the exhaust.
How much does a 18inch diameter double walled stainless
exhaust pipe weigh that is 6 feet long?
Turbines don't need water so why use it.