European boat diesel ventilation

Discussion in 'Diesel Engines' started by RoyHB, Oct 2, 2010.

  1. RoyHB
    Joined: Apr 2010
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    RoyHB Junior Member

    New Jeanneau boats have a forced air ventilation system that runs whenever the engine is on. The ventilator is a fairly noisy fan in the engine compartment connected to a large diameter exhaust host to the transom.

    Slightly older Jeanneaus have a similar system that uses a thermostat to turn the fan on when the temperature reaches a certain limit.

    I have an idea that the constant running fan is there because of some EC regulation rather than an absolute engineering requirement.

    Can anyone confirm (or refute) my opinion?

    If the ventilation is only there for european compliance then I would consider adding a thermostat to the blower on out boat.
  2. TeddyDiver
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    TeddyDiver Gollywobbler

    Most compliances are required for items sold for consumers so you can do pretty much what you wan't just don't sell it without "uninstalling" your own tunings..
  3. Aliboy
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    Aliboy Junior Member

    As well as heat, you also need to be concerned about the absolute air flow available. Restricted air flow can kill your engine. A rule of thumb is that you need 1 sq inch of free flow per hp. i.e. for A 100HP engine you want 100 sq inches of unimpeded air intake. I have noticed on many modern boats that the intakes are sized much less than this, and the solution is to use fan forced air. Of course the engine at lower speeds needs less air flow, so the 1 sq inch rule is based on allowing the engine to operate OK at full power. If you only operate at lower speeds you can get away with less air flow. In your case this might mean having the fan turned off. If you were to fit a switch on the fan, I would use a vacuum (pressure) switch rather than a thermostat if such a thing is available.
  4. Dean Smith

    Dean Smith Previous Member

    it matters not where your boat is, your airflow must compensate for ambient temp and rise above that in the E/R I
    spent over 20 years commissioning engine systems, many in marine applications, and found that inadequate ventilation was the #1 cause of performance and fuel consumption complaints in marine engine rooms. Yachts typically the worst, offshore oil platform engine spaces usually the best, everything else usually somewhere in between.

    CAT, Cummins, MTU, Mak, and just about all the others I know of publish guidelines for engine room ventilation, almost all universally ignored by builders and installers in my experience.

    In general full load intake air restriction (with clean filter/silencer) should be less than 5" H2O, compared to atmospheric pressure. Best practises I have seen try to limit ventilation air temp rise across engine space to less than 10 degrees F, and try to keep air temperature to air inlet within 5 degrees F of outside air temp at full rated load.
    Now the above para is NOT mine , it saved me writing it
    If you go to a Cummins or Cat site they will tell you what air you need
    i too have done around 50 install, 32 of them my own
    Engine air supply is a big issue
  5. AhoySailor
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    AhoySailor New Member


    So you would have to make conversions to a boat in order to bring it from Europe to the US?
  6. Aliboy
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    Aliboy Junior Member

    I think that this is a design issue that is not restricted to Euro boats. The engines don't care what country they are in, just how much air they get to breath.
  7. Mark Cat
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    Mark Cat Senior Member

    ABYC H-32 Ventilation of boats using diesel fuel.


    32.4.4 Ventilation. The changing of air within a compartment by natural or mechanical means. Ventilation may be affected by dilution of contaminated air, by local exhaust of contaminated air, or by introduction of fresh air.

    32.5.3 Combustion Air. Ventilation provisions and openings to the machinery space provided for supplying combustion air shall accommodate at least the sum of the maximum air requirements specified by the engine manufacturer(s) for each propulsion and auxiliary engine(s) in that space.


    1) Consult the engine manufacturer(s) for combustion air requirements, including inlet air temperature and restriction/depression.

    32.5.4 Additional uses of ventilation. Power or natural ventilation may be needed to control compartment temperature. Power ventilation may also be used in the machinery space for odor control and personnel comfort while servicing equipment.

    For overall engine room design ventilation, engine and fuel shut down in case of fire, alarms, and fire extinguishing system(s) must be designed to work together.

    Many times crew comfort limits engine room under extremes of ambient to 40 degrees C. Also, the engine room temperature needs to be well controlled in order to properly select and size equipment.

    ABYC sets maximum engine room temperature at 50 degrees C.

    You can design for rise relative to ambient, or the system can be staged to provide more air exchange as engine room temperature increases.

  8. powerabout
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    powerabout Senior Member

    you can calculate the fan sizes by getting the btu output of your machinery and then any AC guy will tell you from ambient how much air to maintain a max temp.
    Of course you need to add the engine air consumption as well
  9. CDK
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    CDK retired engineer

    The blower can do little benefit for the engine itself. A 2liter diesel running at 2000 rpm pulls in 4 m3 of air each minute, with or without blower and expels it through the exhaust. If more combustion air is desired, a turbo charger is added, not an engine room fan.

    Perhaps the fan pulls air from the engine room to the transom to keep the warm air and possible diesel smell away from the cabin. It is the only valid reason I can think of to install an unnecessary noisy fan.
  10. Frosty

    Frosty Previous Member

    I would say it was to prevent heat build up after turning the engine or engines off.

    Normally the engine itself uses and removes massive amounts of air.

    But when turned off is a huge lump of stored heat with its own oily aroma.
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    FAST FRED Senior Member

    Normally the engine itself uses and removes massive amounts of air.

    Cruisers in chilly places have been known to use this ton of iron for heating.

    If a vessel has a circ water heating system , a bit of inginuity with the plumbing will allow the cabim heater to function with a small DC circ pump .

    No engine room smell!
  12. powerabout
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    powerabout Senior Member

    If the only air access ( as on a commercial vessel)is via a fan then the fan has to keep up
  13. Mark Cat
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    Mark Cat Senior Member

    A lot of good posts, but I think perhaps we should be clear as to engine room requirements per engine HP and equipment and crew comfort.

    More specifics on Engine Space Ventilation.

    My rule for commercial:

    Ventilation must supply combustion air and keep engine compartment temperature rise within 15 degrees C relative to ambient.

    Dave Gerr for pleasurecraft:

    Recommends 17 degree C maximum delta.

    Recommendations from Dave:

    Heat exchanger or Raw Water Cooled Engines with Wet Exhaust:

    Minimum Vent Area (sq. in.) = hp/3.3
    Minimum Airflow (cu. ft./min) = (2.75 x hp) - 90

    Good rules of thumb from Dave. However, the engine manufacturer can provide the requirement for combustion air with either a wet or dry exhaust and if keel cooling is used.

    More from Dave:

    Above 500 hp, blowers are required at a minimum of 33% of recommended airflow.
    From 750 to 1000 hp blowers are required at a minimum of 50% the recommended airflow.
    Over 1000 hp, blowers are required at a minimum of 100% the recommended airflow.

    This is also good general information from Dave.

    I specify the use of power vent(s) for engines below 500 hp. The reason was mentioned in one of the prior posts. Manly, heat soak. The waste heat generated after the engine is shut down. A small power vent used to maintain engine compartment temperature can also be used to vent during heat soak.

    So I add the requirement for forced ventilation to keep the machinery space within 15 degrees C of ambient after engine shut down.

    In specific terms I like to establish the max engine room temp at 45 degrees C (for crew and equipment) and stage the blowers. 5 degrees less than ABYC 50 degrees C max.

    It is important that power ventilation produces negative pressure in the machinery space. That is, it pushes air out of the space. It does not suck air in. If you need to blow in and suck out for a very large installation, make sure to maintain slight negative pressure in the engine room at all times.

    Power vents must work with the fire extinguishing system for shut down or closure during a fire.

  14. masalai
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    masalai masalai

    From memory, on my little Kubota 21hp engines the specification was for 150sq-centimetres inlet (150mm x 100mm) and 100sq-centimetres outlet (100mm x 100mm) flow by natural venting...

    An experienced builder suggested, '... on return from an outing, so that normal operating temperatures are achieved, close all normally closed hatches/vents, - - then runn the engine up at full throttle in neutral, (not over-revving lest damage is done), then after a while, open the main engine hatch to see if the engine increases in revs due to air starvation...

    The desired answer, if you do not feel like you have opened an oven, and the engine revs do not surge faster then natural/existing ventilation is about adequate...

    I would be more inclined to blow air in rather than suck it out as that may reduce air pressure in the engine room and cause air starvation and over-rich running, causing nasty problems...

  15. CDK
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    CDK retired engineer

    On my Scandinavian boat, originally equipped with twin stern drives, there is a large vent at the transom, half of it used by the mandatory fan, the other half is for intake of air.

    Also the floor boards over the engine bay look like they seal it completely, but they don't. They rest on an aluminum frame guiding rain water to the through hulls, but recessed parts allow air in as well. Air can also be pulled in from the compartment where the fridge compressor is installed. In fact everything that looks closed, like the sliding glass door to the cabin, has recessed areas where air can pass.

    I have always assumed this was the common way to construct an engine room.
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