kool keel diesel engine

Discussion in 'Diesel Engines' started by carlos bairo, Sep 28, 2010.

  1. FAST FRED
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    FAST FRED Senior Member

    "The exhaust duct has to be heavily insulated to avoid burning your boat, thats it in principle. (really heavy)"


    Most diesel exhausts are about 1/2 the temperature of a car engine.

    Heavily insulated , hardly ,

    I have seen SS stove pipe (insulated double wall, locks together ) used on diesels (real exhaust inside) , simply left exposed, or in a metal lined duct, that had a fan to steal the heat to warm the cabin.

    Far less dangerous as an old VW or Porsche heating system.

    Mass produced items , can be used to great cost effectiveness to lower "Marine" costs.

    FF
     
  2. Vulkyn
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    Vulkyn Senior Member

    So basically a normal diesel engine can be fitted with a keel kooler and proper exhaust to handle the heat etc...
    But doesn't that mean the boat will be pumping out the hot exhaust directly outside? Wouldn't that be a nuisance for people on the deck and other around the boat?
    Or is it possible to fit a wet exhaust for that?
     
  3. apex1

    apex1 Guest

    Fred,
    what is a car engine? And are we talking cars?

    A dry exhaust on a boat has to be substantially insulated, as our entire industry knows, and does.
    It is not only a matter of fire hazard, or injuring crew, a heated engine room causes a lot of additional problems we do not want.

    There are good reasons why the yacht industry does not like dry exhausts, and builders like Nordhavn needed many years to install proper working systems!

    That you have seen sloppy installations does not mean we should recommend them!

    Vulkyn,
    That was done, but means to have the worst of both worlds.

    Regards
    Richard
     
  4. Vulkyn
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    Vulkyn Senior Member

    I dont follow, here is what i understand basically a normal diesel engine (compared to a marine version) would have 2 problems fitting it in a boat, cooling and exhaust.
    Cooling would usually be through sea intake and hence the need for marinizing (or use a normal radiater - guess would get too hot or use a keel cooler).

    The second problem would be exhaust as wet exhaust means the exhaust goes through water and gets pumped out so less smoke smell etc...

    So if i get a normal engine and fit a keel cooler to it and make it a normal dry exhaust i can decrease my problems ...

    So am i on the right track or did i miss something ?
     
  5. FAST FRED
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    FAST FRED Senior Member

    what is a car engine? And are we talking cars?

    Many boats use car engines as stern drives , and others have them below as propulsion.

    Crusaider and Volvo come to mind.These are harder to dry stack , but it is done.

    Many lobster boats chose car engines for low cost , power to get home quickly , and simply toss , rather than rebuild when the engine gets many hours.Change out is an afternoon with the usual d over the engine hatch.

    Dry stacks are exhausted as high as can be done .

    Modern insulation will keep the engine room as cool as a wet exhaust manifold , IF the normal engine room ventilation is "by da book". Large intake ducts and a fan sucking the heat out.

    Modern "hospital critical" muffler system will put out far less noise than thru the transom.

    The transom exhaust will fill with exhaust the aft cockpit with any following wind.

    The hassle with a dry stack is on a roomaran it may mess up the accomidations as it passes through 2 or 3 layers of boat..

    " builders like Nordhavn needed many years to install proper working systems!"

    Hardly , most work boats have dry stack setups ,for half a century+, so there is NO engineering questions , only ones of fitting it to the boat.

    FF
     
  6. apex1

    apex1 Guest

    No no Fred, not hardly, it cost them several years to get their dry stacks designed properly. There are some issues fishermen accept, yachtowners not.

    Nice to see, we agree finally on the insulation effort to be made! Or how shall we translate "modern insulation"?
    Redesigning the engine room for a dry stack was not what I was referring to, when I said, that heat radiation into it will be a problem when insulation is insufficient. Of course that is not the case when I can address it from the very beginning in my design.

    Seems you like to contradict for contradictions sake, not for better arguments!
    What have the petrol engines to do with our topic?

    And donĀ“t you think I know already which sort of Diesel engine is used in most boats???
    Car diesels are the minority, for sure! Most of the marinized, or just keel cooled / dry stacked, are industrial, truck, or tractor engines. Read: heavy duty engines by design, and not handgrenade set for max on road power.

    Your statement about the "as long as possible" exhaust is wrong! As short as possible is the right way from a engineers point of view, due to the backpressure in long exh. pipes. And therein lies one of the problems with dry exhausts, you need a long run for clearance, but a short one for performance.

    The next issue with a dry stack is soot collection. You have to build a cleanout "sack", where soot and moisture (mainly condensate) can be removed.
    Another one is the fact that you never can use raw water for compressor cooling, watermaker, and the like, without getting the "no sea water inside the boat" idea thwarted.
    And so on......

    It is as it is in our business, there is NO best solution. They all have severe disadvantages, no matter how one likes to argue.


    No, you just have different problems, not less.

    The wet exhaust is not only cooling the fumes, the more important part is the manifold jacket, which is water cooled. That removes substantial heatloads from the engine room. No need to describe the advantage.



    Regards
    Richard
     
  7. FAST FRED
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    FAST FRED Senior Member

    "And therein lies one of the problems with dry exhausts, you need a long run for clearance, but a short one for performance."

    Most boats have little problem with running a larger diameter pipe. The flow from 6 inches is better than 4 , the ability of 8in is great far and away above what the usual 50 ft would need , and pipe is cheap.

    There is no problem with a dry stack with water cooled exhaust manifold , plumbed into the keel cooler , with the rest of the engines waste heat.

    The only downside is COST for the manifold.

    A used wet manifold from a common engine might cost less than a good modern insulation jacket.

    Most dry stacks have at least a 90deg turn at the top , to keep out rain, steaming into the wind there is a chance the boats velocity helps the exhaust leave.

    Exhaust length tuned to the engine might be of great value on a 50cc 15,000 rpm racing bike , but many modern truck marinizations have turboes which precludes a tuned .exhaust , it just needs a low pressure way off the boat.

    "Car diesels are the minority, for sure!" You bet , except for "picnic Boats" and ski boats with BMW Yanmars.

    However in many fisheries simple gas car engines are the choice.

    Seldom found on pleasure boats , except on the great lakes , where high speeds for short periods of time , running marinas , is the norm.

    Car Gassers (tho usually all wet exhaust) make sense where the season is short and the distances minor.

    FF
     
  8. Carteret
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    Carteret Senior Member

  9. BTPost
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    BTPost Junior Member

    Not just the commercial Fishing Industry.... but just about every vessel over 100 Tons....
     
  10. apex1

    apex1 Guest

    True, when finetuned to:
    ...but just about every commercial vessel over 100 Tons. Yachts, even the biggest, sport wet exhaust mainly.
     
  11. FAST FRED
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    FAST FRED Senior Member

    Yachts, even the biggest, sport wet exhaust mainly.

    Yachts are not ordinarily brought back to the dock in sub freezing temperatures , unloaded , and left for a day or a week with no "winterizing" and then operated.

    Winterizing a wet exhaust takes time and money , and you only need to slip up ONCE! for it to get expen$ive!

    FF
     
  12. apex1

    apex1 Guest

    Right Fred!

    But we are not talking fishing craft, but yacht here!

    And I would say we can end this senseless debate anyway. There is no best way, just different ones, as we all know.
    So each one has to pick his poison.

    Regards
    Richard
     
  13. singleprop
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    singleprop Junior Member

    heat exchanger and keel cooling

    This discussion raised a question: can a heat exchanger cooled engine can be connected to a keel cooler (in other words, circulating the keel cooler fluid through the heat exchanger instead of circulating raw water through the heat exchanger)?

    I assume that this can be done IF the keel cooler is really large (say 60 gallons of fluid inside the keelbox)..

    In some keel cooling set-ups the engine over cools so one benefit of this approach would be that the heat exchanger can be used to control the engine temperature, thereby preventing over cooling and cycling of the thermostats....

    Any down sides to this approach, will the system work?
     
  14. TeddyDiver
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    TeddyDiver Gollywobbler

    Yes to both questions. It could be done and there are drawbacks. Better to run the cooling fluid directly to keel cooler and use the heat exchanger for better purposes like warming tap water or boat heating.. Keel cooler most usually is a tube running along the stern part of the keel.
    Dave Gerr has made an article series about the subject in the Professional BoatBuilder http://pbb.proboat.com starting from issue 111 page 66. It's also in the Boat Mechanical Systems Handbook by Dave Gerr.
    BR Teddy
     

  15. singleprop
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    singleprop Junior Member

    Hi Teddy,

    I would expect that the heat control of the engine would be better managed by using the heat exchanger (circulating the keel cooler fluid through it) since it has been sized for the engine, whereas it requires "precise caluclations" to make a keel cooler fit (not using a heat exchanger). If the keel it self is used as the cooler, and it is big enough then all the engine heat could be transfered to the keel (which then dissipated the heat through the metal)then it is just a matter of connecting the keel cooler to the heat exchanger...I think...

    What draw backs could you think of?
     
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