Engine Room Ventilation

[claymore]

At the Boat Show I bought 2 vetus vents, 2 lengths of flexible pipe and an extractor fan.
I'm going to mount 1 vent on each side of the wheelhouse with the ducting pipe going down to the engine area.
1 will let fresh air in, the other will have the extractor fan attached and will be used to draw out the air which usually smells a bit hot and whiffy.
Question. Do I set the in pipe lower than the out pipe on the grounds that warm air rises therefore the whiffy stuff will be higher up or does it not really matter?
Ideally the out pipe would be lower because its easier to mount the extractor fan lower.

 

[Nauti Fox]

What size is the engine and is the air intake inside or outside the engine room?

 

[IanPoole2]

Depends - after a few pints of the black stuff, king prawn vindaloo and a few rum and cokes, I'd have the exit low down. If you smoke old shag on baord - as high as possible.

You need to check the personal habits of your crew who may be down there

 

[jimi]

Rather than have an extractor fan its a better idea to have a intractor. The reason is that more air reaches the engine and obviously with more air in the boat and higher air pressure it tends to stop oil leaks and helps to keep your craft afloat. Hope that helps

 

[ccscott49]

Should be OK wherever you put it.
Does the engine breath inside or outside the engine space? The reason I ask, is if it breaths outside, the extractor, can be left on when the engine is running, if it breaths from within, the extractor, should only be used when the engine is not running.

 

[claymore]

Thanks Colin
It breathes from inside and its a 48hp engine. There are 4 vents (I think) - 2 of which are in the wheelhouse, which let air in there but I was thinking to extract the air once the engine is shut down.

 

[Sgeir]

Our Eberspacher (spelling?) inlet is in the engine area, so it's very effective at blowing warm diesel/oil fumes fumes into the saloon. Certainly improves things in the engine area.

But I was thinking, once you install the new chimney, I'd strongly suggest an in-situ annual inspection by a very small person. I don't know if anyone immediately springs to mind?

 

[Nauti Fox]

If you've already got 4 vents into the engine room and are only extracting when its stopped don't really see the need to fit another inlet hose.
Might save a bit of work.

 

[boatmike]

Doesn't really matter. Also you are right to extract not blow in as any leaks from a pressurised compartment will come out where you don't want them. Advantage of low down is it will clear any gasses that settle in the bilge. Only reason to have it high up is if you have batteries in there. Hydrogen is lighter than air..... Bit theoretical though. It will be extracted anyway unless you have an engine room the size of a tanker.
Engine will draw air in anyway. Purpose of engine room extraction is to keep air circulating and keep temperature down. One thing you could do is put a timer switch in circuit to switch the fan off say 10mins after the engine is shut down....
On a big ship system the calculation of fan and duct size is important. Too big an extractor fan with too small a duct on the inlet and you can starve the diesel of air. On a small boat all you need is a very low capacity fan and keep the inlet duct bigger than the outlet (if you have ducts at all of course) Remember the fan and the engine are working in unison to draw air in but only the fan is blowing out....

 

[boatmike]

Not so. Most large ship engine rooms have constant extraction for the reasons stated in my post to claymore direct. The inlet capacity needs to balance the extract + engine consumption though.

 

[boatmike]

It's a boat Jimi not a bloody air balloon!

 

[tcm]

Re: Engine Room Ventilation - sensiblish answer

i wd set the outlet high cos hot air rises, and harder for water to get in, and towards the stern. I wd also set the inlet high and towards the stern, as below.

I wd not worry bout starving the engine of air cos the engine will defintiely pump in the air in needs, no bother, unles that vetus is one hell of a blower, and it almost certainly isn't strong enuf to deny the engine any air - it is a fan, and not a positive-displacement machine which wins it's air by positive displacing (shoving) the air from one place to another like an combustion engine or Rootes-type blower (eg a supercharger) - and it will easily suck air in through a fan, which sort-of waves at the air hopefully with masive scope for slippage if there's any demand for air

On mobo's all the axshul holes are high, with inlet on one side (port/starboard) extractor on t'other so an airflow is set up across the ceiling of the engineroom which the warmest wiffiest air throughout the engineroom is then easily able to join. Otherwise, you may merely set up a flow of vertically rising air in one area. Also, if it's dead hot and the extractor is knackered, the air can get out anyway.

I wd seal up any connection towards living area, and just have vents sternwards/sideways/rear quarters. I wd also use an absoute minimum of pipe, cos the pumping losses will be massive innem - mobos have disguised holes in the side of the boat, not pipes. I wd also make the fan the highest-up thing if any pipe is connected to it , so any water comes out rather falls inwards to the fan and rots it. Also, any inlet pipe should slant upwards into the boat of course, for similar reasons.

 

[claymore]

Re: Engine Room Ventilation - sensiblish answer

Thanks Matt
appreciate the advice