Air cooled sailboat motor

Discussion in 'DIY Marinizing' started by 8ball, Feb 7, 2016.

  1. Steve W
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    Steve W Senior Member

    I installed an air cooled 10hp Sachs Wankel in a new cold molded 26ft sailboat I built back in the 1970s.We did as Gonzo suggested and ran a pump off the engine and fabricated a water cooled exhaust to avoid the challenge of running a hot exhaust thru the boat. We used a clutch and a watermota variable pitch prop with no transmission.
    One thing to keep in mind is that you need to supply plenty of air to the engine so it cant be as enclosed as a water cooled engine and can be a bit noisy but a gasoline engine is inherently quieter than a diesel so it may not be too bad. The Wankel had pretty much zero vibration.

    Steve
     
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  2. 8ball
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    8ball Junior Member

    That's possibly the first Wankel powered boat I've heard of. The problem with running a pump off of my engine is there's nowhere to drive it from.
     
  3. Yobarnacle
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    Yobarnacle Senior Member

    Use an electric pump. Your engine will have an alternator won't it?
     
  4. 8ball
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    8ball Junior Member

    I did consider an electric pump, I have several sitting on the shelf here in front of me. That would certainly be an easy thing to arrange.
     
  5. FAST FRED
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    FAST FRED Senior Member

    "Air in the engineroom or engine box should be higher pressure than outside ambient pressure.
    blowers/fans should all be driving air to the engine.
    You don't need or want exhaust fans in the engine enclosure.
    The engine itself is pumping a huge amount of air from it's environment, through it's valves and cylinders, and out the exhaust."

    This might be fine in a commercial vessel with air tight bulkhead pass thru fittings , but in a 30 ft boat is very dangerous.

    A pressurized engine room can easily spread exhaust fumes or even fire into the cockpit or cabin.

    With 10hp the engine power loss from an ER exhaust fan raising the engine altitude would be zero!

    And an extracting blower is the Law in most countries on a gasoline boat.
     
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  6. gonzo
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    gonzo Senior Member

    The Law requires an exhaust fan to prevent fumes from entering the rest of the boat. On large boats or ships there is a combination of intake and exhaust fans. I think that may be overkill for a small boat.
     
  7. Yobarnacle
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    Yobarnacle Senior Member

    I spent 43 years aboard large ships and large sea going tugs.
    One stack blower was permanently forced draft, the other switchable to use as an exhaust fan when in port and cold iron.
    It was always reversed to normal forced air draft, both feeding engine room, when the mains were fired.

    but I'll defer to you gentlemen.
    Never ran a gasoline powered ship or tug.
     
  8. 8ball
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    8ball Junior Member

    I have a blower to ventilate potential gas vapor from the engine space prior to starting the engine. Once running the engines integral fan will draw fresh air from outside through vents and then the now heated cooling air up and out through exhaust vents. I used to run large trawlers and they always had intake blowers to the engine room that ran continuously when underway.
     
  9. gonzo
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    gonzo Senior Member

    Gasoline fumes create a problem not seen on ships that run on heavy oil.
     
  10. philSweet
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    philSweet Senior Member

    I am having trouble visualizing how engine's cooling fan is going to force additional airflow through the compartment. I think you should assume it just mixes the air in the compartment (which is undesireable). Separate duct blowers should be used to ensure compartment venting. A pair of 3" 130cuft/min should do. The compartment needs venting equivalent to a water cooled diesel 10 times as powerful. If you can route some cool air straight to the engine fan, that would be good, but often it is awkward, and not cheap in comparison to what you are building. The venting will likely cost as much as the motor and plate.
     
  11. Yobarnacle
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    Yobarnacle Senior Member

    I edited out the dangerous advice in my post on page one.
    Thanks, gentlemen for correcting me.
    Don't want anybody to get hurt.
     
  12. FAST FRED
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    FAST FRED Senior Member

    Many cars today only use a large DC fan with nothing on the engine.

    One of these from the scrap yard SUCKING the heat out would do fine.

    About 12 inches in diameter, be sure you have 2x that area for incoming air.
     

  13. PAR
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    PAR Yacht Designer/Builder

    There's more to air cooled noise than the exhaust. If you deal with the exhaust and both styles of noise, it can be pretty quiet and relatively cool. Heavy wall pipe, well wrapped with an absorption, instead of reflective style of muffling works best, but then there's the rattle can in the bilge, which requires the same treatment. An insulated enclosure, that handles both types of noise. Typically this means a dense airborne noise barrier and an absorption shield. Lastly, because of all the insulation and how it needs to be tight to work effectively, heat becomes an issue, so consider pulling a negative pressure on the enclosure. I'd separate this into two systems, one for the engine compartment itself and the other to supply cool, fresh, outside air to the engine intake. A few clam shells and inline duct fans, sucking the air through the compartment is the best route. If one of the clam shells was ducted directly to the spark arrestor, you can kill two birds with the same stone.
     
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