Mercedes 300 d in my Bertram

Discussion in 'Diesel Engines' started by Gary Chiles, Nov 26, 2019.

  1. gonzo
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    gonzo Senior Member

    Positive pressure in the engineroom is a huge no-no. The fumes will go into the living quarters. Also, if there were to be a fire, it will blow it through the boat. We are not doom and gloom, simply experienced. Wishful thinking will not get your boat up on plane. Finally, the million miles claimed for the Mercedes diesel is not in marine applications where it will run at full torque and power.
     
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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    Theses schemes to adapt road vehicle engines to marine use are largely built on the illusion of considerable cost savings, when generally speaking they are ideas that would be better left as ideas.
     
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  3. Gary Chiles
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    Gary Chiles Junior Member

    Hey all, been abusy couple of weeks. Still waiting to drop the engine in, waiting on the engine heat exchanger to arrive.Due to holidays, budget etc. things are delayed. I do want to let everyone know that Ive solved the ventilation issue,the compartmentation for the engine and transmission in this boat extends all the way to the stern, lots of open space and gunwhale vents so the heat can be pushed easily out with simple squirrel cage fans, nice and cool. Now, another idea for this boat is to put a couple of all weather, high output solar panels on the roof for accessory use and extra power for whatever I use. I plan on getting full electronics for the boat and installing washdowns fore and aft, which will require a little more dc power than the engines will produce. A friend is actually going to give me a system that he was using in his Sprinter camper before he sold it. Question for you folks is, Have anybody out there ever seen this done on a boat? I think it will work fine, Also comes with two big deep cell batteries made for photovoltaic systems, should I anticipate any issues, anything Im missing?
     
  4. kapnD
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    kapnD Senior Member

    If you need a lot of raw water for wash down, baitwell or whatever, a belt driven pump off the main engine is far more effective than multiple electrical pumps.
    A system off of a camper will be a water pressure system, not a washdown, the difference being higher volume, and the ability to run for extended periods of time.
    Solar is great, but you won’t be able to rely on it all the time, (cloudy weather, nighttime) so higher output alternators should be fitted.
    Your motor isn’t going to like having exhaust fans in the ER.
     
  5. Gary Chiles
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    Gary Chiles Junior Member

    Hey Kapn, Yea, youre partially right on the solars about not being too dependable with no sun, Im in San Diego, so usually ,not a problem, especially in the summer. The batteries, when fully charged , with what Ill be drawing , will provide me about 3-5 hrs with no sun. I cant figure out what kind of pump to use for washdowns as far as a pulley driven one, thats going to be a trick, thats why I was going to go electric. I got almost a complete system for free, However, Im not stuck on that, the system might be good as a better use as a backup or just for the sonar and sounder, radio , windlass, etc. The washdowns will be just very intermittent use also.How come you think the exhaust fans wont work?tested one ,just to see and it blew that heat right out of the stern vents readily.Thanks man!
     
  6. fallguy
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    fallguy Senior Member

    Squirrel cages are notoriously low cfm. At least the ones I have seen.

    Your original idea to run in line high cfm blowers was closer, but you said pos pressure. If you run a blower or two in and a blower or two out that meet the cfm needs; that seems better. If you can find a high cfm squirrel; correct me.

    Anyhow, I am only going to offer general support, I am not experienced with a diesel conversion.

    It does seem like the air needs and cooling needs of the engine box need more study.
     
  7. gonzo
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    gonzo Senior Member

    The rule of thumb is to provide 1/2 square inch per HP for a diesel. That assumes no restrictions, including grills are reducing flow.
     
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  8. fallguy
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    fallguy Senior Member

    Is that in or out or both?

    What is a square inch ito air movement?
     
  9. kapnD
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    kapnD Senior Member

    I think what you’re not getting is that your diesel will consume a LOT more air than the old gasser, and it does not like to be denied that. A lack of adequate air for the intake will cause poor performance and black smoke.
    Follow Gonzo’s formula above, be generous!
    Exhaust fans in the ER Are ok to run after the engine is shut down, but not while operating.
    I understand that you are fighting excess heat because your conversion has not taken into account the confined nature of a boats ER as opposed to an automotive environment. A real marine engine uses water jacketed manifold and turbo to reduce heat radiated into the ER.
    Lacking that, you must heavily lag exposed hot exhaust parts and hope that your exhaust system is large enough to carry away the additional heat. You may need to increase the diameter of the exhaust system to accomplish this.
    Concentrate on the issues under the hood first, the powerplant must be the primary concern on any powerboat!
     
  10. Gary Chiles
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    Gary Chiles Junior Member

    I dont know, I just know that with the covers on, mind you, only one engine in right now and only one blower, but pushes air really nice out towards the stern and out the rail vents.
     
  11. kapnD
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    kapnD Senior Member


    Air movement is IN to the engine room, and OUT of the exhaust.
    Multiply the cubic inches of your engines displacement by rpm, then multiply again by the compression ratio to find out exactly how much air your motor needs.
     
  12. fallguy
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    fallguy Senior Member

    Your system won't be positive pressure if you do it right. You'll provide for the air and ambient cooling needs both. But a positive air pressure would mean air cannot leave and thus cool.

    My experience is with houses which generally run negative. An example in a house is say you want to exhaust 800cfm off the rangetop. You cannot do that without providing 800cfm to the house or you are negative. And you cannot provide 800cfm with a 1" passive hole to exit because that WILL create the pos pressure.

    In your case, you need to provide the air to the engines AND if you need to cool the ER some; you need the excess air in the chamber to leave passively or actively.

    It needs to be calculated is all I am saying. Put a pen to it.


    ps
    Gonzo brings a good point about the dangers of pos pressure, but really for all boats; you must not allow any pathways for air to travel back into the living spaces. Here in Minnesota, a little girl got sick onboard and Mom and Dad assumed she was seasick, but she was a canary and the boat got an exhaust leak and when they put her in the cuddy; the fumes were sucked into the cuddy via suction from the cuddy door being left open by the concerned parents and she died in the boat. This inspired our laws here for CO detection in all living spaces.
     
    Last edited: Jan 3, 2020
  13. gonzo
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    gonzo Senior Member

    It is a rule of thumb that has been proven to work well for enginerooms with no forced ventilation. The formula is empirical.
     
  14. fallguy
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    fallguy Senior Member

    Gonzo-I don't want to get into polemics, but there is a problem here. Let me explain.

    so, horsepower estimates are between 140 and 230, call it 200 for the er vent calc

    I read it as he needs 100 square inches of venting per engine. That is like two vents with grills 6x10 per engine. He can't do that out the stern, so he could only do that with openings in the cockpit which would be loud as hell. So something here is not making sense to me. He simply can't use passive venting I would say.

    I apologize in advance, but I have visions of someone cutting big holes in the transom. Since most engine boxes are sealed, his only other option is to move air actively.

    Have I missed the obvious?
     

  15. Gary Chiles
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    Gary Chiles Junior Member

    Yea, maybe a couple of nice marine grade in line blowers in addition would give plenty of fresh air, the extra cfm that I need to avoid fumes to the bow berthing, ( which is small). maybe put them midship to help pull out of the stern.
     
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