Dry VS Wet exhaust

Raider Ronnie

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Keelboater

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Good question. I like the dry stack too. Seems like the commercial guys who run their boats year round would have less issues with dry exhaust. No freezing to worry about, and no "drinking on the job" like your friends boat. But maybe the tuna guys prefer the wet exhaust for better hull efficiency (no keel cooler) and greater speed to get to the canyons? Not that a DE is a speed demon, but a few more knots can cut down on that travel time a bit. I suspect that any emission requirements would apply to wet or dry. Builders who cater to recreational users probably stay away from dry stacks in favor of a little more usable cabin space. There are probably quite a few reasons why the choice is made to go with wet, none of which make the dry stack a bad design that I am aware of. See what other replies you get.
 

Blitzen

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I suppose you could have the keel cooler recessed into a box in the bottom of the boat(more $$$) but most are just mounted to the hull and adds a lot of drag if you are looking for speed and efficiency.
 

Powderpro

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A dry exhaust does not require the engine to be keel cooled. Every boat we build for Alaska is dry exhaust and no keel cooler, so the speed is the same for dry or wet. Heater exchanger cooled engines just pump the water overboard through a thru-hull on the side of the boat. The advantages of a dry exhaust are no water will get into the engine, and you can load the boat way down with fish/product and not worry about getting water up the exhaust. That's the #1 reason that 90% of commercial salmon fishing boats in Alaska have dry exhaust.

The advantages of a wet exhaust are; you have way less exhaust heat in the engine room, less weight, more deck space because you do not have a muffler and shroud mounted on the deck, and a cool sounding exhaust. But a dry exhaust tends to be more quiet than wet.
 

Curmudgeon

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A friend who changed from wet to dry saves 40 gallons a week of fuel now. Most seem to think it is because you are not wasting energy pushing that exhaust all the way to the stern. I have dry exhaust and a heat exchanger. There are plenty of new builds with dry exhaust out there too.
 

petrel

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Guess it also depends on your location. Down south, a hot muffler is not much fun most of the year, but up north could be a nice feature. Dry exhaust also eliminates having to get enough drop for the water. Heat exchanger and raw water pump makes for a king hell bastard of a washdown.
 

Raider Ronnie

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jwalka51

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Im getting ready to re-power. I currently have a wet exhaust. With the new power I will be fabricating a dry system with a good muffler. I am sick of the wet system, the one that I have right now is loud as fuck. I am going to go with a heat exchanger cooling option though.
 

jwalka51

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Another advantage of the dry exhaust is that On a new build you may be able to mount the engine low enough that It will be completely below deck and eliminate the engine box. Whereas with a wet system you would need to have the extra height.
 

Raider Ronnie

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captjohn

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You can go with a water lift muffler if you want a wet system with the engine mounted below the water line. There on just about every sailboat, and a lot of really large sportfishing boats.
 

jwalka51

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The guy who ties up right next to me has a 31 bhm with a cummins 6BT 210 HP. He has a dry exhaust and the engine is mounted completely below the deck. The thing has a ton of deck space. In my opinion, this is the # 1 reason to go dry. If you can have the whole cabin engine free and have a full deck, then you are maximizing the useful footprint of your vessel. In my opinion, anyone who builds a new boat that is big enough for their chosen power to fit below deck, but does not because someone talked them into a wet system, is a fool. Why waste all that valuable space, not to mention all of the possible problems that come along with the wet exhaust.
 

Powderpro

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A friend who changed from wet to dry saves 40 gallons a week of fuel now. Most seem to think it is because you are not wasting energy pushing that exhaust all the way to the stern. I have dry exhaust and a heat exchanger. There are plenty of new builds with dry exhaust out there too.

I've never heard of saving fuel going to dry exhaust, but I've never switched from one to the other on the same boat. As long as back pressure for either system is within manufacturer's spec, fuel burn should be the same.

On my dry exhaust systems, the bottom flange of the muffler is mounted at deck level, the muffler is wrapped with an exhaust blanket and the muffler is contained in an aluminum box/shroud that is vented on the sides and top of the shroud (see pic)

DSCN9004.jpg

DSCN9006.jpg

DSCN9028.JPG
 

jwalka51

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They can fail. Just look at the articles that Tony Athens has posted. You will see many examples of engine destruction due to wet exhaust systems of every type. The only component that you can count on 100 percent to keep water out of your engine with wet system is gravity. If you put your engine below the water line with a wet system, you are asking for a disaster, period. Magic muffler or not, its not a matter of if, but a matter of when.

Read his articles, you will walk away with a very different understanding of the wet exhaust system.
 

Toolate

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I've never heard of saving fuel going to dry exhaust, but I've never switched from one to the other on the same boat. As long as back pressure for either system is within manufacturer's spec, fuel burn should be the same.

On my dry exhaust systems, the bottom flange of the muffler is mounted at deck level, the muffler is wrapped with an exhaust blanket and the muffler is contained in an aluminum box/shroud that is vented on the sides and top of the shroud (see pic)

How far can you shoot that bucket on startup?
 

BillD

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An engine taking a "slug" of water or not out there rolling around on the the big blue seas is simply:

pic#1 = "maybe taking a slug"

versus

pic#2 = "preventing a slug"

The spillover point ;)to the turbo MUST be high enough above the waterline for ALL sea conditions.

An extra 6-8 inches can make all the difference !

Terry Jason Cummins 1.jpe

6BTA High Riser exhaust.jpg
 

Curmudgeon

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If you already have a fresh water cooled exhaust manifold, just plumb the raw water to go overboard instead of into the riser elbow. Remove the riser and change it to a dry stack. It will depend on what type of engine and how the cooling system is set up.
 

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How do you design the muffler? Anyone know? Obviuosly you have to achieve the correct back pressure. Do you just make sure there is more than enough flow through the baffles? I've made them before but just copied an old rusty one so I didn't design it.
 
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