Keel Cooled Diesel

Discussion in 'Boat Design' started by Capt. Flint, Sep 24, 2018.

  1. boatbum10
    Joined: Jan 2012
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    Location: Warrenton, Oregon

    boatbum10 Junior Member

    Most keel cooled diesels do away with the rubber impeller pump, and then the fresh water cooling/circ auto style pump already on the motor is upsized. Many diesels also have a keel cool pump option through the engine manufacturer. Some of the older cats used a belt driven pump to supplement the circ pump for keel cooling applications (it was not a rubber impeller though, more like a steel centrifugal pump).

    If available the factory tank like the post above work well. Or you can build an aluminum or stainless header tank to mount above the motor. Weld on or bolt on radiator cap fittings are available to put on the tank. You may need to run small hoses from several high points in the engine cooling system direct to the tank to avoid an air lock. Or there may already be petcocks on the motor to drain air off the top manually, which is ok. Once the system is purged of air it shouldn't be an issue if you keep up on the coolant level.

    On your keel cooler, keep air purging in mind. On boats with lots of rocker (shaped like a banana), air can be trapped in the back end and prevent coolant flow. I've seen a small valve in the lazarette to bleed air when initially filling the system. Or keep the cooler shape such that where it penetrates the engine room is the highest point.

    Make sure to design a proper exhaust stack. Not only the steel side with expansion/wrinkle belly section and such, but proper air flow through the trunk. I imagine you'll see 500-700F exhaust pyro temps at the engine and not much cooler up the stack, so trunk design and insulating wrap are important. You can insulate the messy way, or have some one like this build custom wraps Marine Insulation | Insulation for Boats | West Coast Insulation https://www.wcinsulation.com/
     
  2. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    D Gerr in the Boat Mechanical Systems Handbook has good chapters about the subject. Get it as there's so much more in the subject convenient to discuss on the net..
    Teddy
     
  3. gonzo
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    gonzo Senior Member

    A wet exhaust can be used dry without any modifications. Simply disconnect the water supply.
     
  4. philSweet
    Joined: May 2008
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    Location: Beaufort, SC and H'ville, NC

    philSweet Senior Member

    You can also find water cooled exhaust manifolds. Some are small volume, and some include the expansion tank as part of the exhaust manifold. I found a pair for a 3408. Guessing you need just the right or left one. You have to get the plumbing dead right wrt engine oil cooler, gear oil cooler, engine, exhaust manifold takeoff bypassing tstat, tank. The ability to use a secondary pump to cool the iron after shutdown can make life much nicer in hot climates.
     
  5. M&M Ovenden
    Joined: Jan 2006
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    M&M Ovenden Senior Member

    Complete agreement on getting a copy of "Boat Mechanical Systems Handbook " . He does a good job of laying out the pros/ cons of both systems, and you might decided to stick with a wet exhaust. Done properly they are pretty effective.

    Cheers,
    Mark
     
  6. M&M Ovenden
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    M&M Ovenden Senior Member

    What ? I think that is a bit of a stretch without knowing any construction details. I would think most wet exhaust systems can't be run dry.

    Cheers,
    Mark
     
  7. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Most wet exhaust manifolds are cast iron and there is no problem running them down. He would have to use a metal band clamp to join a pipe to it.
     
  8. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    Have you thought of looking up the wealth of info on Youtube eg



    Heat exchanger here, but its a big one
     
  9. M&M Ovenden
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    Location: Ottawa

    M&M Ovenden Senior Member

    Sorry, thought you were talking about the entire wet exhaust system, not just the manifold.
    Mark
     
  10. DanT
    Joined: Oct 2018
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    DanT New Member

  11. gonzo
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    gonzo Senior Member

    Sure, that would set the hoses on fire.
     
  12. TeddyDiver
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    TeddyDiver Gollywobbler

    Yes, those articles are the very same as in the book mentioned above. Best source AFAIK..
     
  13. Magnus W
    Joined: Nov 2017
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    Magnus W Senior Member

    My keel cooled boat used the engine circulation pump to cool the engine and oil cooler. The impeller pump drove another circuit for the gearbox and after cooler.

    You could probably run the entire cooling circuit with the engine circulation pump. Crucial is to keep the speed of the flow high enough (2 m/s). One way to approach the problem of increased resistance is to do the math. More common is to overdrive the circulation pump by say 10 percent with a smaller pulley. If neither is an option you can fit an electrical booster pump (common in cars nowadays) than can work parallell or inline with the mech pump.

    For tank I had a welded thingy with a regular cooler cap on it (as on old radiators). Just make sure it's big enough to handle the expansion of the coolant (15 percent air volume vs coolant gives you a nice margin).
     
  14. Owly
    Joined: Oct 2016
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    Owly Senior Member

    My concern about keel cooling using tubes, etc would be marine growth. You have something more below the WL for algae and barnacles to grow on that must be cleaned and antifouled. I understand the appeal of a keel cooler as opposed to a heat exchanger, but a heat exchanger can be dry when not in use.... a keel cooler cannot be.
    To my admittedly ignorant mind, this looks alike a significant liability.

    H.W.
     

  15. Magnus W
    Joined: Nov 2017
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    Magnus W Senior Member

    I see your concern.
    My application does not have tubes but use the hull as a side for the tanks that the coolant runs through. Works well but we have fairly cold water and the hull is aluminum (good heat transfer).
    If your boat is wood or frp I guess copper tubing is the way to go. And since most anti foul use copper is guess your problem is solved right there.
     
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