Before TT pollutes your mind with his confused views on this subject
rolleyes
, here's an alternate view....
Both wet and dry have their advantages and disadvantages. The advantage of wet is no lost interior space for a raceway for the dry stack, and depending on the motor that is about it. I make that qualification because some motors seem to produce more soot than others. My CAT 3306, for whatever reason, produces almost none if run correctly. If you have experienced a sooty motor, and will have one again with a dry stack then wet starts looking pretty good.
The advantage of a dry stack is no salt water, no salt water pump and impeller to wear out, additional space in the ER, and no possibility of back pressure in the exhaust if the stack pipe is correctly sized. And if you have a clean engine, less labor to clean exhaust residue than with a wet exhaust - the later obviously a function of what have you got to do the cleaning, type of engine, etc.
Good comparison. Pollution will be minimal.
I totally agree that both have their advantages and disadvantages, and it’s nearly a draw, hence the heated debate. I often argue that the things that matter the least get argued the most, simple because it doesn’t matter and is a draw.
For me it was two things, noise and soot.
Noise I think is implementation specific, but our 60 I think was unacceptably loud. I used the fly bridge exactly once, and that was pre delivery to verify everything worked. It was otherwise too loud for my taste. Mid 70s dB as I recall, with a throbbing probably exacerbated by the hardtop. I didn’t want to be up there. A while ago I was well down the path of adding a second muffler to quiet it down, until the math showed unacceptable back pressure unless I increased the whole exhaust from 5” to 6”. So that project got put on the back shelf.
To me, a wet exhaust is loudest in the cockpit where I am least likely to be when underway. Now this may be different for different people. We are about the scenery, not about fishing. If you are about fishing, you might arrive at a different conclusion. No one size fits all.
Re soot, from what I can tell, there are two types. Flakes of soot that land in the deck and make a mess, and a steady mist while underway that coats everything is the airstream.
Many boats suffer the former, but we were spared. We never had soot flakes, and I thank the EPA for that and clean running engines.
What we did have is what I think every diesel has, a constant mist of grime over everything down wind of the exhaust. With a wet exhaust this coats the sides and transom depending on where the exhaust exits. On our dry exhaust it coated everything on the stack including all the instruments and sensors. Believe me, it’s way easier to clean your boat side or transom from the cockpit or a tender, than to clean every instrument on your mast 35’ in the air. Now in fairness, this again depends on the details of your boat and where everything is located. But for us it was a giant pain in the ass. And as you would clean the mast/stack, all that crap would wash down over the rest of the boat. I have shirts permanently stained with black dots.
Lesson 1: just because fish boats do it doesn’t mean it’s good for you too. Evaluate with a critical eye.
And on a more minor annoyance, anytime we had a tail wind of more than about 15kts, the exhaust plume would blow forward over our weather instrument and report outside temps of 125F. This is one of the non obvious things to consider.
Moving on to sea water pumps, impellers, and keel coolers.....
Hand in hand with eliminating dry exhaust is the assumption of said raw water pumps and associated maintenance. I truly Hate changing impellers. If you have ever changed one on a larger engine, you know what I’m talking about. It is a real wrestling match. There is a huge difference between changing a 2” impeller on a small engine, and a 3” or 4” impeller on a larger engine. That all favors dry exhaust and more specifically, elimination of raw water pumps.
But like it or not, those darn raw water pumps and their impellers just won’t go away. I used to have a wing engine and a generator requiring impeller changes. And now I’ll have a wing engine and two generators requiring impellers. So what’s the harm in one more? After all, the engine NOT requiring an impeller is odd man out, right?
Now lets look at the flip side. Dry exhaust, or more specifically keel cooler, requires maintenance too. They need to be cleaned or you will find temps climbing. And the zincs on them need to be replaced every 6 months or so. So whether it’s changing impellers or cleaning grid coolers and changing zincs, you are doing maintenance on a regular basis.
So what’s the difference, you might ask? Well, since you asked, the difference is whether the work is conducted from inside the boat where it is warm and dry, or in the water where it is cold and wet. I’ll leave it to you to decide. You know where I landed on the question.
