Its better to suck or to blow ?

aerobat77

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Aug 12, 2014
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germany
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What is the better deal to ventilate an engine compartment ? To suck out the air ( by blowers ) or to blow fresh in ? Fumes from gas engines appear to be better sucked out but assuming all is fine i guess blowing in is better ?
 
All boats remove the bilge air with blowers, assuming the engine room is semi tight, fresh air will come in from the engine room vents. Thats the way the USCG wants it. But your in Germany so ...
 
If you ask mega maid, you can go from suck to blow. Sucking is always more effective at removing something as something else has to fill in the void.
 
If you’re trying to remove harmful vapors like fuel vapors, it’s much better to suck them out. You have more control over where they go, and any leaks in the engine compartment will simply allow more air in, rather than letting vapors migrate into other parts of the boat.
 
What is the better deal to ventilate an engine compartment ? To suck out the air ( by blowers ) or to blow fresh in ? Fumes from gas engines appear to be better sucked out but assuming all is fine i guess blowing in is better ?
What's better? The way that all manufacturers currently do it. Suck out the air. Sucking it out is better. It HAS to be sucked out to get the (possible) fumes that would settle low. Suggest you read up on air vs gas fumes and how a bilge is setup with fresh air intake and exhaust fans rather than trying to reinvent what has already been determined to work best by people smarter than me.
 
Suck the air out. If you suck the air in you run the risk of filling the ER with fumes.
 
On the one hand i did not saw the difference if you suck the air out and with this force ( on a semi tight engine room ) new air in by vent ports or blow fresh air in and force the 'old' air out by vent ports.

One could imagine blowing in creates better overall ventilation

But i agree with your experience you have more control by sucking it when a spill occours instead trying to blow it backwards - especially if the blower hose is sitting low in the engine room .

My last 240 sundancer definitely sucked
 
On the one hand i did not saw the difference if you suck the air out and with this force ( on a semi tight engine room ) new air in by vent ports or blow fresh air in and force the 'old' air out by vent ports.

One could imagine blowing in creates better overall ventilation

But i agree with your experience you have more control by sucking it when a spill occours instead trying to blow it backwards - especially if the blower hose is sitting low in the engine room .

My last 240 sundancer definitely sucked
No, it does NOT create better ventilation by blowing air in. See the reason I posted above.

The exhaust hose HAS to sit low. See the reason I posted above.

You could ADD a blower... but the primary means still needs to be by sucking.

Regarding blowing in, though... THERE a good conversation could be had whether the finite amount of air being blown in by a blower is greater than what is drawn in by a running engine or two. I suspect the engine is more efficient.

Oh... yeah, got the Space Balls reference :)
 
Thanks lazy daze !

In theory sucking out creates a small low pressure condition in the engine room ( due to momentum of new air flowing in thru the vents ) and sums up to the low pressure condition the engine itself creates by sucking air . Blowing in would counteract the engine suction partially . Assuming a typical 350 chevy is happy with a 600 cfm carb and a typical ER blower reaches 130 cfm the effect appears not THAT negligible . In theory the engine would be happier with blowing in .

But its not about this but about fumes - i fully agree - and so not a good idea to change the setup .

To bigger diesel powered yachts also suck out or do they blow in? I guess with a diesel boat fumes are a non issue .
 

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