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Thread: Fresh air for 1GM inboards

  1. #1

    Default Fresh air for 1GM inboards

    It was hot during summer, even hotter in the inboard engine bays.
    But there were a couple of things to attend to and waiting for colder days was no option.
    So before squirming into my preferred yoga position astraddle the engine, I juryrigged a domestic heater/fan to blow fresh(er) air into the engine bay.
    I was soon startled by a comment from a well-meaning bystander: "Hey, that's the biggest engine blower I have ever seen. Do you use it also when sailing ?"
    I admit I told him it also worked as a supercharger while motorcruising above 15 knots... I guess he still thinks I am a bit deranged.

    Jokes aside, that got me wondering about where the fresh air for the engines really comes from.

    How much air do the engines need?
    The Yanmar 1GM manual states 150 L/min. That seems to be on the low end. 600 L/min would make more sense for a 0.3 L engine running at 3600 rpm.
    That is only combustion air, so more would also be ok to keep the engine compartment cool.

    What size of outside air supply ?
    At least the size of the air filter intake, so let's say at least a 50 mm (2 ") inside diameter pipe.
    Most recent boats have flexible, spiral wire pipe like in HVAC installations, going from the engine area to a higher (and hopefully dry) place.
    Another pipe allowing hot air exit from the engine bay would also be nice.

    So I went looking but there is nothing like that on my 9M ! No air supply pipes, no muffin fans, no cut-outs, nothing !?!
    The front bulkheads are completely closed. As far I can see, the engine compartments are a closed box.
    The engine bay/lazarette covers are not really air-tight, but add cushions, towels and people on top...

    My engines are running cool, no black exhaust smoke but I am still puzzled.
    Could this be an undocumented modification from a previous owner ?
    Does anybody know what the orginal design was ?
    Where do your inboards get their fresh air from ?

    Choking Puck

  2. #2

    Default Re: Fresh air for 1GM inboards

    On my 9m i found that from the rear of the diesel lockers there is a circular vent at each corner of the transom. I think this vents the engine compartments. I do however need to investigate more.

  3. #3
    Join Date
    Aug 2009
    Southern Chesapeake

    Default Re: Fresh air for 1GM inboards

    I would follow what the mfg. says. Many times the boat builder does not. My cooling system is what they call a balanced system where one blower blows air in ( optimally directed at the alternator) and one blows air out.

    I'm not sure there is any relationship combustion air with the cooling air (although the combustion air will also cool the engine as it passes through). I think Yanmar has a recommended opening size for the combustion air, which should be met.

  4. #4

    Default Re: Fresh air for 1GM inboards

    Hi and thanks for your thoughts and comments.Sorry for reacting late but I have been away for quite some time, unfortunately nothing boat related...Mickydrew, if you can post some pictures it would be very useful ! Thanks.Ggray, fully agree with your advice to at least comply with mfg recommendations, as listed e.g. in the installation manual. The lack of any apparent ventilation/air intakes in my engine compartments is worrying...

  5. #5

    Default Re: Fresh air for 1GM inboards

    Sorry for the delay - when i get a minute, i'll post a picture or two with some info

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