Engine Room/Bilge Vent Fan

[Lee Hadjiosif]

I found that the wire of the in-line vent fan in a 2 or 3" hose was cut by the previous owner. My question is: What turns this fan on/off since I cannot find any related switch. He must have cut it for a reason...Could it be that it always runs when the engine is running? Do I really need this fan on my Beneteau 381? On a second thought... could this be an air intake and not exhaust fan? I looks like a factory install. Thanks.
S/V Adagio

 

[Clark]

Lee, you might try posting your question in the Bene Owners area as well.

 

[redhead78]

Pulling air into your engine compartment and moving heat out can only be a good thing. When I repowered my boat, the engine manufacturer said I needed a fan to exhaust the heat from the engine bay mainly because of the 100 amp alt I added gets very hot. Diesels need air also. Ita a 1977 jeaneau, so it had none, fact has them come on wf engine ign, I installed a seperate switch, just me.... Red

 

[higgs]

I have a blower in my engine compartment. I ran temperature tests and found that temps did not vary when the blower was on and when it was off.

 

[wflowe2]

I understand the need for fans in the engine compartments of gasoline engines to vent explosive fumes before you start the engine. Not sure why you need on in a diesel.

 

[Chris Patterson]

I'm surprised to hear the result of no temperature change either on, or off. I'm soon going to power air through the engine compartment, just figuring the hot air little Westerbeke makes, I'd rather it go out a cowl vent, than radiating into the boat. True, venting a diesel is not as important as a gas burner, fumes, etc. But heat going out would be a huge thing for me.
And finding a blower that could withstand running long periods without burning out would be a plus too.

 

[RAD]

I have a center cockpit Oday with a 4 cyl. Westerbeke that gets the engine room real hot and I hooked a bilge blower to one of the aft facing cowl vents and it makes a real difference keeping heat out of the forward and aft cabins plus helping keep ice longer, at times when just going out for a sail the engine isn't on long enough to matter but long trips without wind and motoring for 10 to 12 hrs I notice the difference

 

[higgs]

RAD - did you do temp measurements?

Chris: I have never had a problem with a blower running constantly while under power. when running gas engines that was standard procedure for me and I can only think of one time, after many, many hours, one of those fans crapping out.

 

[tkanzler]

Most of those inline blowers (axial fans) have flow ratings around 125 cfm free air, which means no connections to it, or even measured with a bellmouth inlet adaptor. Connect to corrugated flex with rough interior, make a bend or two, add an exhaust louver and an intake screen, and you're moving half that amount or less.

The amount of heat an inboard diesel, even a small one, will shed to the interior while running is a Goliath to the blower's diminutive Samson-esque air movement. The engine intake will likely remove more air (probably around 70 cfm for a 100 cid 3-cylinder 4-stroke) than the blower.

If you want it to keep the smell down when docked and sleeping on the boat, go for it. For keeping the engine cooler, I suspect it's like spitting on a frying pan.

 

[RAD]

RAD - did you do temp measurements?

I've been meaning to get one of those cheap remote thermometers to watch the temps but I can tell you I've put my hand in front of the vent and warm air is coming out and I'll shut the motor and leave it running till I get all the dock lines,electric,sail covers,etc and I've did the hand test and can feel it much cooler

 

[Gunni]

I found that the wire of the in-line vent fan in a 2 or 3" hose was cut by the previous owner. My question is: What turns this fan on/off since I cannot find any related switch. He must have cut it for a reason...Could it be that it always runs when the engine is running? Do I really need this fan on my Beneteau 381? On a second thought... could this be an air intake and not exhaust fan? I looks like a factory install. Thanks.
S/V Adagio

Is your alternator OEM or an high-output aftermarket alternator? If it is OEM then you don't need a fan, the natural ventilation works fine. If it is a high output alternator you want cool air flowing across the alternator to keep the internal temperature sensor from limiting output, or if no sensor - from burning up the alternator.

 

[John Holden]

Engine fan

The engine fan should come on at engine start and shut off at engine off. I don't believe there is a separate switch. More than likely dit is an exhaust van to remove any vapors. Seems strange that the owner would cut a wire rather then disconnect.
Regards
John

I found that the wire of the in-line vent fan in a 2 or 3" hose was cut by the previous owner. My question is: What turns this fan on/off since I cannot find any related switch. He must have cut it for a reason...Could it be that it always runs when the engine is running? Do I really need this fan on my Beneteau 381? On a second thought... could this be an air intake and not exhaust fan? I looks like a factory install. Thanks.
S/V Adagio