Dry Stack is where it's at ... Conversion Thoughts?

Discussion in 'Powerboats' started by mrwright, Jan 17, 2012.

  1. mrwright
    Joined: Nov 2010
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    mrwright Junior Member

    A while back, I posted a threat about whether to keep my little diesel engine or repower with a gas 350 on my 31' Trojan. After a lot of research, I've decided to keep the diesel. So, here's what's next:


    The Isuzu C240 Diesel engine I have is currently set up for a keel cooler (engine, trans) and raw water cooling in the manifold only. In fact, the water enters the manifold right at the outbound end of it and essentially just cools the tip of the manifold before water and exhaust gases mix and go overboard.

    The Setup
    Since I have to install a keel cooler anyway, it would be easy to add a little extra capacity to keep the engine cool without raw water exhaust. Then, thru-hulls for water would be closed up. The current manifold is wrapped to keep heat to a minimum and I may be able to use it. Exhaust would be routed up through the floor in a 3 or 4" pipe with a truck muffler. That would be enclosed in 8" stove piping and boxed in. The stove piping would be vended so there should be plenty of engine room ventilation.

    The Rationale
    The entire setup for this dry exhaust never enters the cabin due to my boat's design - noise and heat should be at a minimum.
    Exhaust gases are routed 7' up from the deck courtesy of the piping.
    This setup in the end should be easier to maintain and last longer.
    Less thru-hulls at the end of the conversion - always a good thing
    Still able to keep my keel cooler and cabin heater + hot water setup.
    It's different and therefore cool.
    If I ever needed to repower, I could use a truck engine with minimal marinization.

    So what do you think? Anything you would add?
  2. TeddyDiver
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    TeddyDiver Gollywobbler

  3. Easy Rider
    Joined: Oct 2009
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    Easy Rider Senior Member

    Why do you have seawater in the exhaust manifold? Why not engine coolant?

    Easy Rider
  4. mrwright
    Joined: Nov 2010
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    mrwright Junior Member

    i have no idea ...

    that's a darn good question! i didn't marinize the engine so I can't tell you what they were thinking other than the fact that it does cool the manifold sufficiently but it enters the manifold about 2" from the end. it looks kind of like an "add-on" and I can't really understand how introducing raw water 2" from where the exhaust line picks up is really helpful (though it would cool the connection between the rubber exhaust and HOT manifold) ... thus leading me to believe that the raw water can be cut off and the manifold will function fine with dry exhaust.
  5. tom kane
    Joined: Nov 2003
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    tom kane Senior Member

    It pays to be aware that any water injected directly into an exhaust manifold (not a jacketed one) that the pulsing of the engine gasses will back up against the valves and may cause sticking valves and rust and corrosion.
    A common problem with older style exhaust systems. A dry exhaust must be the best choice in this respect.
  6. Gian Milan

    Gian Milan Previous Member

    316L, stainless steel.
    Tig welded in a workshop in which stainless steel is not contaminated from iron.
    You'll see that the there is not problem.
  7. sean9c
    Joined: Jan 2011
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    sean9c Senior Member

    1 person likes this.
    Joined: Oct 2002
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    Location: Conn in summers , Ortona FL in winter , with big d

    FAST FRED Senior Member

  9. whitepointer23

    whitepointer23 Previous Member

    i think he means it is a standard industrial or truck manifold with a water injected exhaust outlet.
  10. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Sea water injection at the exaust outlet into the "injection elbow" just pror to where the exaust hose (wire wound reinforced marine rated) connection is the normal set up for water cooled exaust. Exaust pressure from the running engine prevents any backflow into the engine. Having said that you should install a vacuum break fitting(vented loop) on the water injection supply hose to prevent water getting into the engine when it is not running due to possible syphoning.(see post # 12) . One rule i always follow is to close the off this supply whenever i shut down the engine. Three other important considerations is the muffler also be rated as a waterlock type(collects residual water in the system when engine is shut off to prevent it getting into the engine) and the system also include a one way device as part of the gooseneck run and a flapper on the exaust pipe where it exits the hull. These three features prevent seawater from being driven into the exaust system and on into the engine from following seas when the engine is shut off. This happened to us on a big sailer in the Sea of Cortez and we almost lost the boat with a non functioning engine after losing the mast. My choice of wet exaust systems has always been Vetus. If you can get your hands on a catalogue or look them up on the internet the proper parts plus the engineering is all layed out for you. Due to fire hazard Dry Exaust are frowned upon by many insurance companies and usually require such to be engineered and inspected by a certified person. While i'm on the subject of wet exaust it might also be a good idea to install a exaust cooling alarm in the run. That way if you forget to turn on the sea water exaust coolent it will intise you to do so. My preference is a wet exaust where ever possible. They are less of a fire hazard, run quieter, and less downdraft fumes.

    A yacht is not defined by the vessel but by the care and love of her owner--
    Last edited: Feb 2, 2012
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    FAST FRED Senior Member

    Remember IF you have room a hanging locker vented from the exhaust stack will dry lots if gear with no effort.

    DRY clothing beats wet 10,000-1!

  12. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Some clairification on my prev. post, (post #10) too many long hours preparing the land yacht brain wasn't working at it's normal low level of dumbness :). First there are two types of wet exaust systems -one in which the raw cooling water is injected into the exaust from the output of the engine heat exchanger. The other is if the engine is keel cooled then the water to cool the exaust is run from it's own sea water pump usually thru a second valve after it's sea cock to control the volume to the exaust. Set the flow so the exaust hose is a just a little more than warm. Say between warm and a little to hot to keep your hands on it. In both cases I recommend a vented loop fitting as waterlines change with cargo and that change might just be enough to create siphoning.
    "Also the statement that insurance companies frown on dry exaust" meaning they are a little more vigilant due to possible fire hazards and in this case the OP is considering a change from a wet exaust to a dry exaust. The onis is on owner to report this modification to his insurance company otherwise in case of a fire it is possible the coverage could be voided. --Geo
    P.S. Fast Fred I do like the added feature of captured heat from a dry exaust. To get this from a wet system one needs extra fittings hoses, a radiator and a fan-- more gear and more electricity consumed.
    Last edited: Feb 2, 2012
  13. michael pierzga
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    michael pierzga Senior Member

    Careful with heat buildup in the engine room. Double the blower capacity

    Every keel cooled dry exhaust boat ive dealt with has been a workboat. I dont like the idea of a yacht with cabins running dry.
  14. Gian Milan

    Gian Milan Previous Member

    There are motors designed to fit on a ship (several are, RR, Caterpillar, Volvo Penta, Isotta Fraschini and so expensive. Etc...)
    There are also others who were born to a cooling of a certain type.
    When you change an engine to put in a boat, do a good job if
    cooling does not change the rules.
    What I personally do?

    Replace the radiator with a heat exchanger ( (I do it cylindrical, exterior and interior, including pipes, stainless steel 316L).
    water heat from exchanger is sent to the muffler, muffler replaced by one twin-chamber, stainless steel 316l.

    Since an automotive engine air and preys not on the boat, increasing the capacity of the oil pan that is cooled in a heat exchanger from the water which then goes into the radiator heat exchanger.

    The sea-water first cools the oil and the cup, then cools the radiator fluid, then ends up in the muffler.
    The muffler is very quiet and does not transmit heat in the boat.

    One great advantage, this.
    Doing it this way, the engine works perfectly because the design parameters are maintained.
    I keep the mail.
    I have great fuel economy, although some problems for the correct position of the oxygen sensor.

  15. viking north
    Joined: Dec 2010
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    viking north VINLAND

    Often on steel build hulls the keel cooler is simply a pre fabed long rectangular open top steel box(s) inverted and welded to the skin. This is designed in such a manner it becomes part of the structure. Simply weld in a female threaded pipe nipple each end and screw in pipe barbs to accomidate the supply and return engine glycol coolent hoses. This keeps the exterior hull free of appendages and reduces the danger of rupturing the keel cooler(s) in the case of a grounding.
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