Engine Room Fans. Suck or Blow. ?

Well.....to suck out means you need somewhere for fresh air to get in...and to blow in you need somewhere for the bad air to get out.

I would say suck out because this will take out bad air etc....blowing in will need a sealed engine room apart from one route out..if not you might get bad air etc coming through all the small holes in engine bays etc.
 
If you blow in, the engine air requirement may cause the fan to run overspeed and burn out. Arrange suck out ducting to be over hottest part of engine to remove maximum heat. This is often over the turbo-charger area and exhaust manifold outlet..
 
Mine blow into the engine room.

I think it depends on fuel: my petrol speedboats used to vent the engine room to remove dangerous fumes; with the diesels that I have now, the fans increase the air supply to the engines. Not massively necessary in the UK but makes a difference in the hotter temps down here in the Med.
 
I don't know what is normal but I have both - some fans that blow into the e/room sucking from outside, and some that suck from e/room and blow outside (that turn off when engines run). The latter just help in cooling the e/room when engines are stopped. I also have plain vents, not fan assisted at all.

Suck vs blow is not important for cooling the e/room when engines are stopped - you can create N changes of air per minute whether you suck or blow. But when engines are running hard you want fans that suck air from outside and blow it into the e/room. The maths is compelling - I need to get a cube of air (at atmospheric pressure) 50x50x50 metres into my e/room every minute at cruise speed, so blowers help and suckers don't.
 
A comment, I've worked in the engine rooms of various old tugs, coasters, trawlers and assorted rustbuckets, and without exception, they all had a powerful fan and ducting blowing outside air in to the engine room, the air coming out of the ducting near the engine air filter/inlet manifold. Unpowered ventilators at the top of the E/R to let out the heat and smells.
 
Even with an open vent to the outside do not blow into the room unless you are certain that fumes can't be forced into the cabin.

By far better to suck out. If petrol engine suck near the bottom to get the fuel fumes (heavier than air).
 
All about the airflow into the engine compartment. Engines when running at different RPM will require differing amounts of air flow, depending on how efficiently the intake vents work it may be necessary to force more air into the engine room or just move airflow through. Many larger yachts will have variable speed or even reversible fans to accommodate different air flow requirements at different speeds.
 
Bob Stay said:
A comment, I've worked in the engine rooms of various old tugs, coasters, trawlers and assorted rustbuckets, and without exception, they all had a powerful fan and ducting blowing outside air in to the engine room, the air coming out of the ducting near the engine air filter/inlet manifold. Unpowered ventilators at the top of the E/R to let out the heat and smells.
Click to expand...

Having served on commercial vessels before bridge control engineers used to huddle under forced air fan duct by engine controls, in the Red Sea temperatures were evil. Good trick if you were off watch was to take a large bag of dried peas from the galley go onto the funnel casing and empty the peas down the engine room air intake. The howls from the engine room were pitiful especially if any of the recipients had a touch of sunburn!

However on a more serious note, most engine manufacturers recommend drawing air into the engine compartment with exhaust fans as this reduces the amount of air borne debris in the engine room.
 
Latestarter1 said:
Having served on commercial vessels before bridge control engineers used to huddle under forced air fan duct by engine controls, in the Red Sea temperatures were evil. Good trick if you were off watch was to take a large bag of dried peas from the galley go onto the funnel casing and empty the peas down the engine room air intake. The howls from the engine room were pitiful especially if any of the recipients had a touch of sunburn!

However on a more serious note, most engine manufacturers recommend drawing air into the engine compartment with exhaust fans as this reduces the amount of air borne debris in the engine room.
Click to expand...
Where would the debris come from LS, if you were in open sea with a spotless e/room?
 
My Skilso seems to be a good design.

The engine room fan sucks at just under deck level hence getting the hottest air. This is then ducted to the de-mister outlets on the windscreen.
 
I have 4 engine room fans, each side the forward one sucks in and the rear ones blow out. Just a load of hot air!
 
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