Wet Or Dry Exhaust – Which Is Best?

We have discussed the merits and demerits of wet and dry exhausts in the past. After much study, and dialog with commercial and pleasure users, we opted for a wet system on Wind Horse and saw no reason to change with the FPB 64s. Recently we were challenged on this subject, and after answering, challenged again, with the point (amongst others) that Nordhavn has been successful marketing dry exhaust systems. Which brings us an axiom we learned long ago. To wit, successful marketing and good results in the real world of long distance cruising are rarely synonymous. Rather, it is better to execute based on first principles and sound logic.

Since you already know which side we come down on, we thought it would interesting to share the opinions of two former Nordhavn owners, now FPB clients, who have lived with dry exhausts,

Let’s start with the comments of John Henrichs, who, with his wife Sandy, used to own a Nordhavn 64.


Don’t even get me started on this one. We had a dry stack on the Nordhavn. I won’t spend a lot of time on it, but here are the good points and bad points.

The Good:
1.  No raw water pump.
2.  A little less back pressure on the exhaust system.
3.  Maybe a little more efficient for the engine.

The Bad:

1.  Soot. No way to prevent it. Each time you start the engine, there will be soot. Even in electronic engines as the soot is a by product of combustion. Each day we had to run the engine at max power for 10 minutes to clean out the stack. After docking we had to wait for the stack to cool and then put a cover over it as if rain or moisture gets into the stack you will get a lot of soot on your next start up.

2.  Keel coolers. In warm water they need to be cleaned about every 2 weeks. If not, engine can over heat. Keel coolers need zincs which in warm water need to be replaced about every 2 to 3 months.

3.  Cost. A good dry exhaust system is more expensive to build.

4.  Exhaust leaks in the system. Each system will have several flanges with around 8 bolts and a thick gasket. After time the gaskets get brittle with heat and need to be replaced or they will start leaking.

5.  Heat.  There is a lot of heat in the dry stack and you will need a good supply of air to cool the stack. We had a 2000 cu ft fan to suck the air out of the exhaust and had two 2000 cu ft intake fans.

I could go on longer, but I wouldn’t ever do it again. Many of my Nordhavn buddies feel the same.



I forgot to mention that Bruce Kessler went around the world in a Delta 70 with a wet exhaust and never had an impeller failure.

Don Stabbert has been across the Pacific and Atlantic on his Northern Marine Starr and hasn’t had a impeller problem.

I have over 25,000 miles on wet exhaust boats and haven’t ever had a impeller or raw water pump failure.

In the diesel class I just attended, the instructor spent time on the subject and explained the dry start (no water on the blades) is what causes impeller failures and once running the impeller runs on a thin film of water for lubrication. He also said failures once running are rare.

Next, lets hear from Pete Rossin who prior to converting to an FPB 64 cruised with his wife Debbie on a Nordhavn 50.

Hi Steve

I did have dry on my Nordhavn.  Here were the issues – some of which were bad design, material selection, etc.  Some are the nature of the beast.

First, my muffler was carbon steel and rusted out in 5 years.  Due to the design of the boat, I had to remove the entire mast/stack assembly to get it out – a big deal.  Switched to a Hapco stainless muffler and no rust issues after that, but as the muffler was wrapped in insulation, the only way I caught the fact that it was rotten was a slight rattling sound I was hearing in the stack chamber.  Had it gone much further, there could have been a fire. The need to remove the stack to change it was s design issue – a mistake you wouldn’t make.

Issue 2 was that it was dirty on start up and the exhaust would occasionally belch black clinkers that would make a big mess. You need to be dead certain that rain and spray can’t get into the exhaust when the boat sits idle – it compounds the problem.  The exhaust also has to exit high enough over the boat that it blows cleanly away – this may result in a boat with a higher clearance then you would like.

The lower exhaust sections were double walled with an annulus that was connected to two air injection fans for cooling.  They chose cheapy Dayton fans which constantly failed – again, a mistake you wouldn’t make.

The related issue was keel cooling – I don’t like it.  Keeping the keel cooler clean was a major hassle and there was an instance where one  owner hit a reef, destroyed his keel cooler and wrecked his engine.  Having a keel cooler out there is a big vulnerability, especially with your bullet proof hulls this is the achille’s heel.

You already know the primary argument for dry – no salt water, but if you need salt water for your shaft log, watemaker and genset and have a bullet proof system like the 83 and 64 – what’s the big deal?  Particulalry in the case of the shaft log, going dry would mean a separate pump to provide the cooling water for the shaft seal – just another thing to go wrong.

You pick your poison, but I believe wet is a better choice.


We rest our case (if you have real world experience to bring to the discussion we’d like to hear from you).

Post script: use the SetSail search function to dig up more on wet and dry exhausts.

Posted by Steve Dashew  (May 24, 2011)

13 Responses to “Wet Or Dry Exhaust – Which Is Best?”

  1. David Says:

    The advocates for dry exhaust often site that 99% of commercial fishing vessels use dry exhaust. Other than the soot issue (commercial vessels not as concerned), why is there such a disparity between cruisers and commercial vessels?

  2. Keith C. Says:


    I would add that the space a dry-stack typically takes up, in what is usually some of the best real estate aboard a vessel, is another serious down-side to the dry exhaust.

    Keith C.

  3. Steve Dashew Says:

    Hi Keith:
    You have hit on an important point. By the time you add exhaust diameter, insulation, space for air circulation, muffler diameter, and attachment fittings the volume is substantial. Add to this the noise issues – this is taking place in the middle of your living area – and the balance in favor of wet exhaust grows.

  4. Max Says:

    Hi Steve,
    Seems to me that the FIRST question to be asked when making ANY purchase is,
    “How much user experience does the designer have?”
    Nothing beats experience. (Like yours.)

  5. Kent Says:

    I am not sure I see much differance between a hole in the boat for a keel cooler or a hole in the boat for a water intake for a water pump. Either way you have a hole in the boat.

  6. Chris Says:

    Lost a lot of respect for the ‘discussion’ on this site in the last 24 hours…

  7. Steve Dashew Says:

    Hi Chris:
    Sorry you feel that way. We are nNot sure what generated the heated debate on exhaust systems, but we try and let folks call it as they see it.

  8. Dieter Says:

    In a metal boat there is no need for a hole for a keel cooler, the cooling surface is normally welded inside the hull as a heat exchanger.
    As a protection against rain in the exhaust you can use a cap as they are commonly used on ovens, like the Dickinsonmarine “DP” Cap.

  9. John Poparad Says:

    “successful marketing and good results in the real world are rarely synonymous”

    my generalization for your specific.

  10. Perriot Says:

    We had this question when we make the drawing of Hoa.
    one of the advantage of the dry exhaust is : no “salty wet air” can come back in the engine after it was stopped (hot air became colder and suck humidity in) it’s mean less potential corrosion in another hand for pass a dry system with enough insulation through arrangement it is quit impossible (except if your engine room is located aft ,behind your arrangements)
    But also dry exhaust could be a necessity if you have keel cooling or “tanks cooling”,for boats working in area with ice or in river with lot of leaves or small wooden part in water.
    On Hoa we choose wet exhaust, but with more room we would choose dry exhaust.

  11. Steve Dashew Says:

    H Perriot:
    HOA sounds like an interesting vessel.
    Condensation is a problem with both wet and dry exhausts. If you design the wet exhaust system so that there is a dry riser pipe, and then inject cooling water at the top, so it can all run out after the engine stops, the exhaust will quickly dry out once the engine is shut down. If you are still concerned with salt air, then the exhaust valve can be closed when the engine is not in operation.

  12. Perriot Yannick Says:

    Hi Steve

    One another advantage of the dry exhaust (if it’s high enough ) : you don’t navigate permanently in your exhaust gas !
    Some designers for wet exhaust choose to put the outlet just under the water line and perpendicular to it (for exp. On motor sailor Sopranzi 50’)
    Sure with wet exhaust going out aft in trade winds you can traveling in your own smoke.
    A well know Belgian sailor became seek by the exhaust gas when he motoring with his ketch in long calm,he sleeping in the aft cabin and the gas make his way through the portholes…
    Sorry for my English but I am not young and …French !
    Since the beginning of the « adventure »  of the building of FPB 83 and later 64
    We follow with interests the FPB series so close to our concept of real passage maker.
    (except for the design ,we like boat looking « retro » like 1930 motor boat )
    Unfortunately our boat is similar in lot of points …except for the load of gears !(particulary the Koop Nautic !!)

  13. Steve Dashew Says:

    Hi Again Perriot:
    Being washed by exhaust can happen with any exhaust system. With the FPBs we have not found this a problem except when going directly upwind if standing on the swim step or by the transom what we call the station wagon effect).