Petrol Engine Compartment Blowers - current thinking.

[moresparks]

Hi, Looking for current safety advice regarding engine compartment blowers for petrol engines.
I have a late 80's early 90's Sports cruiser with twin VP AQ171C engines, these are fitted with twin carburetors. The compartment has 3 in-line blowers One blower is controlled on the dashboard this extracts air no problem. There are 2 other blowers, one feeds air in and the other extracts, tracing the wiring for these blowers and I find that the supply feed is fed via a relay, the relay "signal" wire is fed via the engine key-switches with the take-off via the carburetor idle solenoids feed!!!
All the fans are working as intended - but - this means that the "engine" fans are on all the time the engines are running and they are noisy - (louder than the engines at idle). Of course turning the engines off, turns off those fans.
I understand why and happy for this to continue, but just wanted to check if this is still current thinking.
I have an Insurance Survey in the next few months so trying to offset any potential problems.
Thank you.

 

[spannerman]

Blowers on sports boats don't usually run all the time, only seen it on bigger boats.
All American boats I have seen have a sticker by the helm saying run the blowers for 4 mins before starting the engine. So as long as you run the blowers before firing up you should be fine, the important thing is where the air is extracted from. It should be at the lowest point in the engine room as petrol vapours are heavier than air and will accumalate there.
I run mine before start up and while at idle going in and out of the marina as I get a bit an of oil fumes smell at low speed which disappears when the engine is running at cruise as then all the fumes get sucked into the engine.

 

[MapisM]

and while at idle going in and out of the marina as I get a bit an of oil fumes smell at low speed which disappears when the engine is running at cruise as then all the fumes get sucked into the engine.

This is the crux of the matter. At idle, a petrol engine sucks very little air, possibly not enough to grant a sufficient e/r ventilation.
I would think that this is the reason for the apparently overkill setup that the OP describes.
Now, personally I would also be happy with manual-only blowers (which in fact is what I've always had on all my petrol boats), knowing that it's better to turn them on whenever using the boat at very low rpm for some time.
But the OP is also concerned about a survey, and I wouldn't be surprised if the surveyor would raise some objections to the removal of the automatic activation.
Btw, carbureted engines are usually more prone to releasing vapours...

 

[jrudge]

All my Fairline’s ( 40 /58/65) have had constant running blowers.

Remember they maybe required for general ambient cooling as well as fuel vapour removal ( not an issue on my diesel boats).

Unless you feel it is a retro fit I would leave it as per the manufacturer

 

[moresparks]

Hi Many thanks for your responses its greatly appreciated.
The Blowers are low down so that's not a problem. The blower installation looks original factory fit from Fairline. It would be nice to have more control and re-wiring them wouldn't cause too many problems. But, providing this method is still approved, I will stick with it.

 

[jrudge]

I didn’t know it was a Fairline. They all have forced ventilation.

 

[Portofino]

With a carburettor engine I think they need upmost caution in a boat .

I have recently acquired a classic quad carburettor ( 4 twin barrel Webber’s ) Ferrari and it basically always smells petrol of fumes .
And yes all the rubber fuel pipes have been renewed .
Of course unlike a boat it’s openly ventilated as there’s a grill over the engine and the bottom of the engine compartment is open along with ventilation from the rear wheel liners .

Fuel injection petrols or diesels are completely different kettle of fish with regards to exploding fume generation .
With carbs gaskets and lead plugs can weep n seep ,o rings go + much more .
Works perfectly, just reeks of fuel .

As said I,am assuming your rubber fuel lines are fresh ? If not they perish from the inside out and release vapour .

Some of the above advice has been from people above wearing the wrong hat(s) ?

Then there’s the insurance assessor after the fire who discovers the blowers have been bodged , interesting conversations will follow , assuming you survive the explosion .

So don’t mod it that’s my advice you need every trick in the book to de fume a carburettor engine in a boat , not less .

 

[stelican]

Hi, Looking for current safety advice regarding engine compartment blowers for petrol engines.
I have a late 80's early 90's Sports cruiser with twin VP AQ171C engines, these are fitted with twin carburetors. The compartment has 3 in-line blowers One blower is controlled on the dashboard this extracts air no problem. There are 2 other blowers, one feeds air in and the other extracts, tracing the wiring for these blowers and I find that the supply feed is fed via a relay, the relay "signal" wire is fed via the engine key-switches with the take-off via the carburetor idle solenoids feed!!!
All the fans are working as intended - but - this means that the "engine" fans are on all the time the engines are running and they are noisy - (louder than the engines at idle). Of course turning the engines off, turns off those fans.
I understand why and happy for this to continue, but just wanted to check if this is still current thinking.
I have an Insurance Survey in the next few months so trying to offset any potential problems.
Thank you.

Really do not understand your comment feeds from idle solenoids, Do you mean starter solenoids. I worked for a dealer.
The petrol engined fairlines built during that period only had the engine bay suction fan/ blower operated from a dash switch as standard. maybe someone had added the the suction fans/ blowers.
We did have instances of boats not reaching full power unless the engine bay hatch was lifted but this was 10 years prior to this.
Perhaps your boat was intended for hotter climes and got re imported to UK or was a cancelled export order.

 

[moresparks]

Hi - I must confess I was a little surprised myself regarding the relay feed.
The Solex twin carburetors have a solenoid on the idle valve/jet. I must confess I am no expert so happy to be corrected but my understanding is that it is a device that shuts off fuel to the carburetor after the ignition is turned off to prevent the engine from receiving fuel. A sort of anti-fire device.
In effect this means that 2 of the blowers would stop when the ignitions are turned off.
This just leaves one blower extracting air before and after switching on/off the engines
The carburetors have been fully overhauled and new gaskets etc and all fuel feed lines are copper except from the filters to the engines and it all works o/k.
Maybe another blower controlled by the dash switch on the other side of the engine compartment wouldn't go amiss!!

 

[jrudge]

that would suggest the final fan is for post run cooling.

Given it works what are you trying to achieve?

If noisy you can replace the fans - my t40 used to munch them quite regularly - they are cheap hence seemed to have a short life in the hostile environment of a boat.

Unless it looks like a bodge I would leave well alone! Fans on a petrol boat will have been designed be someone who knew the installation and Fairline for their many sins are rarely daft.

 

[moresparks]

"Given it works what are you trying to achieve?"

yes I know - my sentiments are echoed in Portofinos post regarding safety.
As the boat is nearly 30 years old - Elf and Safety have moved on since , so just wanted a confirmatory opinion what with a Survey coming up, so I have time to make amendments if needed.