rogerthebodger
Well-known member
Any 12 volt explosion proof exhaust fan will be OK to remove petrol fumes from the engine room
Bilge blower type and timer or not?
- Thread starter waynes world
- Start date
moresparks
Active member
Hi, I not sure if this overkill!!!
Personally, I like manual control as you need to run the blowers for around 5 minutes before starting the engine(s), no wake zones, when the engine has stopped and refuelling etc.
With my original petrol twin set-up, I had 3 blowers. 2 were manual controlled the other came on when the engine was started (ignition) and was on all the time. However, the blower that was on all the time, the intake was at the top of the locker suggesting that it was to remove heat (possibly a med specified boat)?? The other 2 were low down to remove fumes.
There doesn't seem to be any advantage to running the blowers while underway for petrol boats, as the boat has built in air vents to direct fresh air into the engine compartment.
If, indeed, the engine(s) run better with the blowers running then they are being starved for air and the vents need enlarging.
If you are concerned, then a “sniffer” may be a wise investment.
Personally, I like manual control as you need to run the blowers for around 5 minutes before starting the engine(s), no wake zones, when the engine has stopped and refuelling etc.
With my original petrol twin set-up, I had 3 blowers. 2 were manual controlled the other came on when the engine was started (ignition) and was on all the time. However, the blower that was on all the time, the intake was at the top of the locker suggesting that it was to remove heat (possibly a med specified boat)?? The other 2 were low down to remove fumes.
There doesn't seem to be any advantage to running the blowers while underway for petrol boats, as the boat has built in air vents to direct fresh air into the engine compartment.
If, indeed, the engine(s) run better with the blowers running then they are being starved for air and the vents need enlarging.
If you are concerned, then a “sniffer” may be a wise investment.
PaulRainbow
N/A
Ignition proof is the key Roger, as you know. If the fan is not ignition proof then it's more dangerous than not having a fan.
moresparks
Active member
Absolutely.. also if the fan is to be on all the time, then it needs to be continuously rated. Some of the “budget” fans are not meant to be on all the time and in some cases (unlikely but not impossible) could overheat
B27
Well-known member
Personally, I'd want the engine to start at a moment's notice.
A gas alarm which detects petrol fumes might be an idea.
It's good to minimise the problem at source.
Don't tolerate fuel leaks.
Make the engine bay self contained and well sealed from the cabin.
Maybe turn off the fuel while the engine is still running, to minimise evaporation from the carbs?
(check whether this is a good idea for your carbs!)
You can also get a lot of smell from a crank case breather, if that's not feeding into the intake.
It's good for an engine to get up to proper temp when running, but if it's giving out a lot of heat when you stop it, that can cause vapour and smell. So be sure the whole cooling system is good.
Any blower dealing with petrol vapour needs to be fit for purpose, not some sparky old brush motor!
Plenty of un-powered convection may be just as good, but a blower may be better for getting the smelly hot air away from the cockpit and cabin.
My mate has a petrol inboard boat, running a small quiet blower for maybe half an hour while the engine was cooling down worked for him.
A gas alarm which detects petrol fumes might be an idea.
It's good to minimise the problem at source.
Don't tolerate fuel leaks.
Make the engine bay self contained and well sealed from the cabin.
Maybe turn off the fuel while the engine is still running, to minimise evaporation from the carbs?
(check whether this is a good idea for your carbs!)
You can also get a lot of smell from a crank case breather, if that's not feeding into the intake.
It's good for an engine to get up to proper temp when running, but if it's giving out a lot of heat when you stop it, that can cause vapour and smell. So be sure the whole cooling system is good.
Any blower dealing with petrol vapour needs to be fit for purpose, not some sparky old brush motor!
Plenty of un-powered convection may be just as good, but a blower may be better for getting the smelly hot air away from the cockpit and cabin.
My mate has a petrol inboard boat, running a small quiet blower for maybe half an hour while the engine was cooling down worked for him.
waynes world
Well-known member
That's all I know. It's one thay came on a new to me boat. Just a blower.
waynes world
Well-known member
@moresparks I have a sniffer but it's old now and not worth fitting so will be fitting a new one. That can be aa you mention overkill with also a blower but rather to much than not enough. Things can fail to much these days.
crewman
Active member
What are you hoping to achieve with your bilge blower? Petrol vapours are heavier than air so will accumulate low down, thus any ventilation needs remove vapours and air from the bottom of the bilge. Industrial gas fired ovens are required to have a prepurge of 5 volumes as part of the start up sequence. This is done by opening all the dampers and putting the combustion air fans on high flow, and in practice takes only a few moments. The logic behind the 5 volume requirement is that if the oven was 100% full of gas (i.e. no air at all) then a 5 volume purge will, in theory, reduce the concentration below 5% (LEL of natural gas). Fitting a small fan extracting from high up will in practice not achieve anything.
waynes world
Well-known member
To remove any flammable gasses. This one is fitted with the duct low down at bilge level. Well maybe 4inch off the bottom.
PaulRainbow
N/A
You have to be 100% certain it is ignition protected. If not, rather than extracting fumes it will more than likely ignite them.
B27
Well-known member
Petrol fumes coming off a warm engine are often warmer and lighter than (ambient) air.
rogerthebodger
Well-known member
The petrol fumes and the surrounding will be at the same temperature and will sink into the bulge
Ambient air temperature is another matter and is not in the engine room
rogerthebodger
Well-known member
Paul I had a look at the info of the Jabsco blowers but I cannot see it that are ignition do you have any info on that fact.
I have 2 jabsco axial fans feeding cool air into my diesel engine room mainy to cool the engine with shut off valves to shut off air in case of a fire
PaulRainbow
N/A
Just had a look on the Jabsco site, they state fans for fuel fumes in engine room, which should mean they are ignition protected, but they make no mention of it.
rogerthebodger
Well-known member
B27
Well-known member
That's only remotely true after the engine has cooled to match its surroundings.
In practice, hot smelly vapour-laden air rises off a petrol engine.
rogerthebodger
Well-known member
The vapour density of petrol is about 2.5 time that of air
And yes hot air does rise compared to cold air but we talk about the RD of petrol vapour at the same temperature as the air in the engine room
If you wish to look at the how the RD of petrol and air change with temperature
Its all depends on th relative density of air and petrol vapor
B27
Well-known member
Oxygen is a bit denser than nitrogen.
Try breathing from nearer the floor....
rogerthebodger
Well-known member
Well I live at 6000ft above sea level so we have less oxygen in the air than you do at sea level so I an very aware of the different concentration of gasses is the air
At sea level is about 21 % at 6000 ft is down to 16.6 % so I am already breathing air with a much lower content that you on the floor at sea level
The power of my car does differs greatly at 6000 ft than it does when I visit my boat at sea level
If your aspersions correct there should be more oxygen at floor level than st head height and the information above confirms that