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Old 01-11-2007, 11:55   #1
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6kw Generator Exhaust or Intake????

I have an Entec 6kw generator and would like to install a blower fan in the compartment. The compartment is located at the stern of the boat. The question is: Should the blower be installed blowing fresh air into the compartment or pulling air from it?
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Old 01-11-2007, 12:10   #2
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Much safer to blow out. If you blew in, whatever noxious vapors you were trying to get rid of would be pushed out, but not necessarily outside.

Brett
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Old 01-11-2007, 12:34   #3
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Good Advice Brett.
Also to add, place a tail on the blower to allow you to suck from the lowest place in the engine compartment. Providing you are not sucking bilge water. Most all Noxiouse fumes and vapours are heavier than air and will settle to the floor area.
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Old 01-11-2007, 13:00   #4
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Has the compartment got a fresh air intake? If not you will need one. Engines need fresh air. They will not operate very well in a vacuum. As for a blower, it should be venting out if you really need one.
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Old 01-11-2007, 14:28   #5
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BOTH Supply & Exhaust is best, but if only 1 fan, Exhaust is essential. Install the Exhaust fan High, and the Supply air duct Low.

Air is required in engine compartments, for two separate purposes:
- engine combustion
- engine room cooling
- Engine compartment ventilation is NOT intended to vent noxious products of combustion, which should be exhausted through the engine exhaust.

An ideal system would provide fully mechanical ventilation - both supply and exhaust air fans.
As implied by Brett, the supply fan might be sized about 10% lower than the exhaust fan (less combustion air), to provide a slight negative pressure in the engine room, thereby preventing fumes entering the occupied spaces.

If engine compartment ventilation is provided by a single fan - it should be an exhaust (extractor) fa,, located in the upper 1/3 of the compartment.

For every 10 above 77 F, an engine may lose 1% to 1.5% of its power output. So the engine room must be supplied with cool air, supplied as low down as possible (lower 1/3 of compartment), and exhausted out from the upper (1/3) part of the engine compartment.

Formulas for engine room air required for engine combustion, and for cooling can be found in most engine installation manuals. Hot climates may require as much as twice the ventilating (cooling) capacity as do temperate climates.
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Old 01-11-2007, 17:15   #6
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As usual I have a different take on this...
Your engines will require about 10CFM/hp. A properly set up and maintained power unit will be smell free. I'd pressurize the engine room. This will allow the engine enough air and if I smell something it means I have a problem.
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Old 26-11-2007, 01:49   #7
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Engine ventilation

Never Monday made a good point. Take a 2 liter, 75 Yanmar. At 2000 RPM it takes ( cca.) 2 liter x 2.000 = 4 cubic meters ( 1.000 gallons) of air just for combustion.
ENgine room is in this way always under slight vacuum. And the ususal ventilators are rarly strong enough to make any really difference. Main function of engine room EXTRACTION fans is to clear the room of fumes before and after the engine runs. But when the engine does run, ventilators do not make much difference.
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Old 26-11-2007, 08:23   #8
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On our boat we have a single 4" diameter exhaust duct leading from the highest point in the engine space to a large continuous duty blower inside the transom that discharges through a clamshell vent and two 4" diameter return air ducts from the transom that terminate just below either side of the engine (a Perkins 4-108). This arrangement discharges the hotest air from the engine space and ensures a good supply of relatively cool, clean, air for the engine. The effectiveness of the system is evidenced by the fact that the engine runs noticeably hotter with the blower inoperable and the fact that, with it, there is virtually no "engine smell" in the accommodation.

Cheers,

s/v HyLyte
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Old 27-11-2007, 20:17   #9
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Pat, I wholeheartedly agree with you on this.

I have seen some engine compartments "buttoned up" so tight that
the diesels are starving for air......i.e. black smoke.

Introducing cool air to a DIESEL engine is a good idea.....

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Originally Posted by never monday View Post
As usual I have a different take on this...
Your engines will require about 10CFM/hp. A properly set up and maintained power unit will be smell free. I'd pressurize the engine room. This will allow the engine enough air and if I smell something it means I have a problem.
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Old 28-11-2007, 02:13   #10
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Professional BoatBuilder magazine issue #110 has an informative article, by Naval Architect Dave Gerr, titled “Venting the Boat” (pages 104 - 117), in which he discusses engine & battery space ventilation and more.

Goto ProBoat Dec/Jan: Professional BoatBuilder - December/January 2007
And Part 2: Professional BoatBuilder - December/January 2007
And Part 1: Professional BoatBuilder - October/November 2007
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