I know we have spoken many times about things so please understand that I am not picking on your design. I have just never seen one like that before. That was why I reccomended discussing it with some experts (which I am not). I have simply had my fill of exhaust issues and the massive havoc they can create - which includes complete failure of an engine(s).the exhaust is pretty much 90% dry water does not get injected back into the exhaust tell just above the muffler. and the picture is a bit decieving the exhaust does slope away from the motor but not a lot. the loop in the exhaust is a good 3' above the waterline. see diagram.
My first concern is what the sulphor and nitrogen diox will do to the galvanized pipe. I really do not know if they would corrode it. Also, the 1.5 seems small for an exhaust size too. The new Yanmars (for example, in the 20ish hp range) reccomend a minimum 2 inch as I recall... with more being better. If you have a long run, tight loops, high risers, etc... that exhaust hose size must be increased to allow for the pressure to get out.
The way you check this is by checking your backpressure. This is generally done on new installs at the factory. They will have the mfg reps/lead mechanic review and approve the install of the engine. This includes the exhaust (which is actually a major part of the install). They do a sea trial and make sure the thing is operating within specs. One of these tests is a backpressure test. It is the only way to be sure you have a proper exhaust.
If you have high backpressure, the cylinders will begin to run hot over time (on water cooled, especically those closest to the rear exhaust which I do not understand why). That heat then causes scoring. The scoring causes very small scratches in the wall. THat then causes compression loss. The compression loss causes engine failure.
I think your engine is a Universal? I do not know the specs for that engine, but I would guess the BP at the elbow should not exceeed about 2psi at WOT. I would need to doublecheck those numbers, but I think that is about right (on a Yanmar). If you exceed about 3 psi, you will eventually have problems unless you never run her long enough to get hot (which causes other problems).
Just some thoughts from the headaches I have dealt with. It is not meant to criticize your install, just to make sure you are aware of these things. I certainly hope you do not take any offense to my comments. I am certainly no "know-it-all". There are many people on this forum that are much more knowledgeable about these things than I am (and maybe you are too). Engines are not my strongest subject.