Blowers: Bilge and Engine Room

RichardS said:
But with most of the examples we seem to be talking about the blower is sucking air out of the engine compartment and therefore tending to de-pressurise the compartment so starving the the engine of air even more?

Richard
Click to expand...

Agree it wouldn't help unless air could flow in to the engine compartment.

The purpose of the blower is to remove the hot air and replace it with cooler air. I have left plenty of air-ways into the bilge where cooler air can flow into the engine compartment. (It is possible for air to flow down the anchor chain tube into the bilge)
 
nigelmercier said:
So every revolution a 2 litre engine sucks 1 litre. At 1200 RPM that's 20 litres (4 buckets) of air a second, being driven by many horsepower.

Any fan that tries to extract air from this space is going to lose, but by all means blow in.
Click to expand...

I'm not sure what you mean Nigel ...... but the fan outlets from my engine compartments are blasting away about the same as SWMBO's mains hairdryer on full power, so they are shifting huge volumes of air.

Richard
 
RichardS said:
I'm not sure what you mean Nigel ...... but the fan outlets from my engine compartments are blasting away about the same as SWMBO's mains hairdryer on full power, so they are shifting huge volumes of air.

Richard
Click to expand...

Blow, suck makes no difference, provided the entry or exit is there for it. It will either be dragging it in through or blowing it out of the correctly sized vent but it will neither blow or suck effectively if the corresponding exit / entry is too small. As with most things you have to consider the entire system not just one component. Which ever way around it should be ducted in low and exhausted high for best efficiency.
 
David2452 said:
Blow, suck makes no difference, provided the entry or exit is there for it. It will either be dragging it in through or blowing it out of the correctly sized vent but it will neither blow or suck effectively if the corresponding exit / entry is too small. As with most things you have to consider the entire system not just one component. Which ever way around it should be ducted in low and exhausted high for best efficiency.
Click to expand...

I covered the "entire system" consideration in post #16.

I was responding to Nigel's suggestion that an extractor fan is not going to overcome the engine intake suction power. This is patently not the case with my extractor fans and I don't have any obvious inlet ports ...... just the gaps around the hatch cover rubber seals. I reckon I must have a serious low pressure zone in my engine compartments and hence the new on/off switch.

Richard
 
nigelmercier said:
So every revolution a 2 litre engine sucks 1 litre. At 1200 RPM that's 20 litres (4 buckets) of air a second, being driven by many horsepower.

Any fan that tries to extract air from this space is going to lose, but by all means blow in.
Click to expand...

It doesn't matter whether you suck out air or blow in air the important thing is to keep air circulating to get rid of the heat.

Does the raw water pump on your boat suck water or blow water?

NOTE
I have now read OP posts (above) and I agree with them.

Clive
 
Last edited:
coopec said:
It doesn't matter whether you suck out air or blow in air the important thing is to keep air circulating to get rid of the heat.
Click to expand...

Yes, for evacuating heat from around a stopped engine. But your link to the "starvation" article implied you were also concerned about combustion air. That obviously has to be blown in - sucking out would be counterproductive for that purpose.

Pete
 
prv said:
Yes, for evacuating heat from around a stopped engine. But your link to the "starvation" article implied you were also concerned about combustion air. That obviously has to be blown in - sucking out would be counterproductive for that purpose.

Pete
Click to expand...

If you suck air out, air will rush in to take it place because "nature abhors a vacuum" (Aristotle).

Clive
 
Last edited:
coopec said:
I disagree

Clive
Click to expand...

I cant see how it makes sense. You have an engine being starved of air, in your example. That means that the engine is creating a vacuum in the engine bay i.e. it is unable to get enough air in to replace the air it is using and thus it has to work harder. Fitting an air extractor could only work to increase this vacuum if the extractor has sufficient power. That would further starve the engine. You need to increase the ventilation i.e. the inflow, not the outflow. The only way fitting an extractor could help is if it was not sufficiently powerful and essentially the engine overpowered it and sucked air in!

I can see no reason for an air extractor in a normal yacht setup other than:
1) to remove gas or other fumes (they should not be there anyway)
2) to remove heat after the engine has shut down (only necessary in a hot climate)
 
pmagowan said:
I cant see how it makes sense. You have an engine being starved of air, in your example.
Click to expand...

The problem is that he's mixing up two different things. One is cooling an engine compartment by getting rid of the hot air, the other is supplying sufficient air for the motor to burn. For the first purpose, assuming there's sufficient ventilation, the fan can blow in either direction. For the second, the one he brought up in post 18, the fan obviously needs to be blowing air into the space for the engine to consume.

Pete
 
I think if we sat down and discussed this matter of ventilation we would all be in agreement.

Engine rooms ventilation is required for two reasons, for cooling the space, and air needed for combustion in the engine.

The air used to cool the compartment improves not only the combustion efficiency but improves the life of the motor. An engine sucking in air at 60F will give a lot more power (10%?) than an engine sucking in air at 120F (hence the need to keep the "engine room" cool)

An engine must get all the air it needs to maintain volumetric efficiency and give full power. As I've said my motor would never starve for air as it draws air from the bilges/anchor chain pipe/dorade boxes so there is no need to blow air into the"engine room".
 
prv said:
The problem is that he's mixing up two different things. One is cooling an engine compartment by getting rid of the hot air, the other is supplying sufficient air for the motor to burn. For the first purpose, assuming there's sufficient ventilation, the fan can blow in either direction. For the second, the one he brought up in post 18, the fan obviously needs to be blowing air into the space for the engine to consume.

Pete
Click to expand...

I was quoting from an article and the author was making the point that some motors aren't ventilated at all - they have to draw air from between the cracks in the floor-boards. Why not ventilate the engine room properly instead of using a blower to blow air in?.

Let's just leave it at that......................................

GEEEEZ!
I'll think twice before I start another thread.
Good night

Clive
 
coopec said:
I was quoting from an article and the author was making the point that some motors aren't ventilated at all - they have to draw air from between the cracks in the floor-boards. Why not ventilate the engine room properly instead of using a blower to blow air in?.

Let's just leave it at that......................................

GEEEEZ!
I'll think twice before I start another thread.
Good night

Clive
Click to expand...

I don't think you need to throw the rattle out of the pram. You made a specific point which made no sense in the context of the link you made. It is only natural that people will take you up on this mistake of either understanding or communication. An extraction fan does not increase the amount of air in the engine bay. It may increase the flow of air through it but this will be in competition with the engine and its 'extractor fan'. To increase available air for an engine you need to either increase the passive ventilation (make big vent holes in the engine bay) or put a fan in that blows air into the engine bay. An extractor would be counter productive.

Where an extractor may help, as you agree, is in reducing the temperature in the engine bay through increasing flow of air through it. Of course, it still needs a vent in which to 'suck' this air in.
 
pmagowan said:
I don't think you need to throw the rattle out of the pram. You made a specific point which made no sense in the context of the link you made. It is only natural that people will take you up on this mistake of either understanding or communication. An extraction fan does not increase the amount of air in the engine bay. It may increase the flow of air through it but this will be in competition with the engine and its 'extractor fan'. To increase available air for an engine you need to either increase the passive ventilation (make big vent holes in the engine bay) or put a fan in that blows air into the engine bay. An extractor would be counter productive.

Where an extractor may help, as you agree, is in reducing the temperature in the engine bay through increasing flow of air through it. Of course, it still needs a vent in which to 'suck' this air in.
Click to expand...

Whatever................................
 
coopec said:
Whatever................................
Click to expand...

:rolleyes:

Well, maybe you are right. If you don't want advice or people to correct you when you are wrong then perhaps you should refrain from starting posts. I am sure there are forums out there where people will just pat you on your back and encourage you in your ignorance. Are you 13 years old? :D Your reply reminds me of a Harry Enfield sketch!
 
You must log in or register to reply here.

Share this page

Top