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Old 20-12-2015, 06:37   #1
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Engine Bay extractor fan

Not strictly an engine issue so I hope this is the best place to pick the collective grey matter on this.

I have a 2010 build Bavaria which due to the EU Recreational Craft Directive (RCD) has a 4in dia fan with 2x 4in diameter air ducts into the engine bay. I'm still no clear on the reasons behind this but I think it has something to do with ensuring the engine has enough air flow to breathe properly.

The fan is connected to one of the ducts and is set up to force expel the air from the engine bay, it is mounted high up on the rear wall of the bay. One could think that this would help reduce the air temperature in the bay but during recent testing I only saw a 5ēC difference with it running. As the engine air filter is mounted closer to the unpowered induction duct, positioned by the saildrive, it can be argued that this single duct should provide more than enough airflow without the need for the (noisy) fan.

So my ponderings are do we actually need to have this fan?

If we remove it we would actually have both 4in ducts available for the engine to breathe through therefore doubling the capacity of air available. It would also massively reduce noise in the cockpit making communications during mooring/anchoring much clearer.

I am considering fitting a simple on/off switch to enable us to use the fan if required instead of it being on all the time the ignition is on.

Please note that this fan is positioned high up so was never meant to be a "bilge blower" and you would not want to use it to clear any gas leak into the bilge as it is not explosion proof or intrinsically safe.

All thoughts and ideas welcomed.


Cheers

Keiron
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Old 20-12-2015, 06:57   #2
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Re: Engine Bay extractor fan

I've actually put such a fan in our engine hole. It provides a slight negative pressure keeping most hot engine smells out of the boat. I've also put it on a timer, on with ignition, off 10 minutes after the ignition is cut.
Is it annoying? Yes. Does it help with cabin temperatures? Yes.


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Old 20-12-2015, 07:03   #3
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Re: Engine Bay extractor fan

See Caterpillar’s excellent paper on Engine Room Ventilation:
http://www.gregorypoole.com/products...ENTILATION.pdf

See also, some earlier discussions:

Engine Ventilation: Skip it?

Bilge/Motor Room Blower Exhaust Port?

Engine ventilation
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Old 20-12-2015, 07:19   #4
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Re: Engine Bay extractor fan

I've found that one pushing and one pulling is the best combo, as long as it isn't a straight path around (or through) the space...

If the noise bothers you that much, you can
1. move the exhaust
2. baffle
3. switch, but I would use a timer...
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Old 20-12-2015, 07:31   #5
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Re: Engine Bay extractor fan

SailMonkey, never considered the slight negative pressure aspect but to be honest we have never had any problems with engine smells within the cabin.

GordMay, thanks for the links I will read them later, however the link to the Caterpillar page seems to be broken as I get a 404 Not Found message. Could you double check and repost?

HappySailor, the noise is not a biggie but not having the fan running does massively improve communications from bow to helm when anchoring/mooring. The exhaust is right by the helm area (twin wheels) and I can't see any alternatives to move it. How would you suggest baffling it? I though maybe some kind of air filter material or "wadding" but not sure if it would restrict the flow too much.

At present the fan is wired so that it comes on with the ignition but not with the engine (ie it runs with the ignition on but before the engine starts) and switches off when the ignition is off. I can't see much point in a timer switch to be honest as it does nothing to help cool the engine really (I could see this working with an air cooled or turbo engine mind). I had thought of a thermostatic switch to activate the fan if the engine bay got above a certain temperature but given the cooling effect is minimal I can't see much benefit from that either.

Research will continue so thanks for the input

Cheers

Keiron
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Old 20-12-2015, 08:06   #6
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Re: Engine Bay extractor fan

Quote:
Originally Posted by kas_1611 View Post
SailMonkey, never considered the slight negative pressure aspect but to be honest we have never had any problems with engine smells within the cabin.

Part of my push pull preference, one larger capacity out... But... We are talking ideals here that may not be required... Boat funds are precious!

GordMay, thanks for the links I will read them later, however the link to the Caterpillar page seems to be broken as I get a 404 Not Found message. Could you double check and repost?

HappySailor, the noise is not a biggie but not having the fan running does massively improve communications from bow to helm when anchoring/mooring. The exhaust is right by the helm area (twin wheels) and I can't see any alternatives to move it. How would you suggest baffling it? I though maybe some kind of air filter material or "wadding" but not sure if it would restrict the flow too much.

I see you point there with the location! My fans (bigger) exhaust off the stern through grills, and all I hear with the plant on is the barely audible fan whoosh... Venting between the pedestals inside the cockpit would definitely fluster me too !

Baffling with some plate just inside the grill would be my idea if I were to keep as is... Unfortunately experimentation and mediocre results are likely part of the process...


At present the fan is wired so that it comes on with the ignition but not with the engine (ie it runs with the ignition on but before the engine starts) and switches off when the ignition is off. I can't see much point in a timer switch to be honest as it does nothing to help cool the engine really (I could see this working with an air cooled or turbo engine mind). I had thought of a thermostatic switch to activate the fan if the engine bay got above a certain temperature but given the cooling effect is minimal I can't see much benefit from that either.

Mine works the same way too... And sometimes I get hung up on "over engineering" My plant is 115hp Turbo... Honestly... I think the best idea is the one you came up with... Just put in a dang anchor/moor/dock/peace and quiet switch! Forget the complications... I'd follow the duct with a wire run and put it RIGHT next to the vent... Then everybody else and yourself knows exactly where the switch is and what it does...

Research will continue so thanks for the input

Cheers

Keiron
Of course the price for admission to the suggestion club is a completed resolution... Pics are a bonus... Not required... but funnnnn....
Good Luck Kerion!
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Old 20-12-2015, 08:20   #7
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Re: Engine Bay extractor fan

Interesting discussion. I think there are some considerations. One is that actively removing air from the engine compartment does inhibit the engine smells... diesel and oil etc. from escaping into the cabin somewhat. My boat exhausts to a grille inside a cockpit combing and this provides all the engine smells into the cockpit ;-). It also blows out some rather warm air. Definitely undesirable in warm weather motoring, but actually an interest feature to have warm air blowing into at least one place in the cockpit.

Some amount of heat reduction is created by removing hot air and this should make the surrounding bulkheads (in Shiva) a tad cooler.

The engine compartment is not air tight and so combustion air is drawn from the air in the engine compartment and then of course through the gaps and so forth. And exhaust fan helps pull air from inside the cabin into the engine compartment and then overboard.
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Old 20-12-2015, 09:15   #8
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Re: Engine Bay extractor fan

I use two four-inch ducted fans. One sucks air from the bilge area and blows onto the alternator to keep it cool. The other sucks from the top of the engine compartment and exhausts overboard (via dorades to avoid taking in water in rough weather). Both are powered by the ignition switch, but in series with a relay connected to the Halon fire extinguisher. In case of a discharge due to a fire, the vents shut down to maximize the extinguishing force of the Halon (old system, still valid for this emergency).
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Old 20-12-2015, 09:16   #9
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Re: Engine Bay extractor fan

Keiron, try
https://marine.cat.com/cda/files/438...%20%281%29.pdf

It’s Caterpillars Application & Installation Guide, “Engine Room Ventilation”, publication #LEBW4971-05
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Old 20-12-2015, 09:49   #10
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Re: Engine Bay extractor fan

Quote:
Originally Posted by kas_1611 View Post
Not strictly an engine issue so I hope this is the best place to pick the collective grey matter on this.

I have a 2010 build Bavaria which due to the EU Recreational Craft Directive (RCD) has a 4in dia fan with 2x 4in diameter air ducts into the engine bay. I'm still no clear on the reasons behind this but I think it has something to do with ensuring the engine has enough air flow to breathe properly.

The fan is connected to one of the ducts and is set up to force expel the air from the engine bay, it is mounted high up on the rear wall of the bay. One could think that this would help reduce the air temperature in the bay but during recent testing I only saw a 5ēC difference with it running. As the engine air filter is mounted closer to the unpowered induction duct, positioned by the saildrive, it can be argued that this single duct should provide more than enough airflow without the need for the (noisy) fan.

So my ponderings are do we actually need to have this fan?

If we remove it we would actually have both 4in ducts available for the engine to breathe through therefore doubling the capacity of air available. It would also massively reduce noise in the cockpit making communications during mooring/anchoring much clearer.

I am considering fitting a simple on/off switch to enable us to use the fan if required instead of it being on all the time the ignition is on.

Please note that this fan is positioned high up so was never meant to be a "bilge blower" and you would not want to use it to clear any gas leak into the bilge as it is not explosion proof or intrinsically safe.

All thoughts and ideas welcomed.


Cheers

Keiron
I suspect this ducting is an attempt at providing cooler combustion air for fuel economy/environmental purposes. Cool air provides a denser more powerful fuel-air charge.
Also there may be an engine warranty element involved.Choking off combustion air in soundproofed "tight" engine rooms can cause several problems beside heat buildup.

My personal experience in trying to provide a hose/duct to the eng. air intake showed that there is a fair amount of engine noise created at the air intake & it traveled up the duct.I had to install a "muffler" on the intake duct.I used a general purpose pleated air filter picked up from auto parts store as used on "hot rods". Works OK.

Cheers/ Len
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Old 20-12-2015, 09:51   #11
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Re: Engine Bay extractor fan

I vent ours right into the cockpit. I want to smell what is going on in the bilge/ engine areas. I also have a shut off for the 4"vent hole right next to me, which we leave closed unless running the fan.
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Old 20-12-2015, 10:49   #12
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Re: Engine Bay extractor fan

Quote:
Originally Posted by Guy View Post
I vent ours right into the cockpit. I want to smell what is going on in the bilge/ engine areas. I also have a shut off for the 4"vent hole right next to me, which we leave closed unless running the fan.
As a side note, that is precisely the same logic at play with a plain hose leading out of the top of the anti-siphon loop into the cockpit (instead of the customary plunger-piston and spring, which can clog or corrode). The occasional squirt of warm water tells you the cooling water circuit is working properly. Smelling the engine room at a distance would, to judge by my experience, the chance to notice a failing belt before it actually went, because they burn as they rub in a quite distinctive way.
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Old 20-12-2015, 12:04   #13
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Re: Engine Bay extractor fan

How old is the fan? The noise issue may be worn bearings or some other issue causing the blades to vibrate. Alternitively it could be tha it is engine noise being 'blown' out, how noisy is it if you run the fan with the engine off? A noise baffle should be easy to make, simply a folded duct lineed with soundproof material.
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Old 20-12-2015, 12:16   #14
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Re: Engine Bay extractor fan

Quote:
Originally Posted by kas_1611 View Post
Not strictly an engine issue so I hope this is the best place to pick the collective grey matter on this.

I have a 2010 build Bavaria which due to the EU Recreational Craft Directive (RCD) has a 4in dia fan with 2x 4in diameter air ducts into the engine bay. I'm still no clear on the reasons behind this but I think it has something to do with ensuring the engine has enough air flow to breathe properly.

The fan is connected to one of the ducts and is set up to force expel the air from the engine bay, it is mounted high up on the rear wall of the bay. One could think that this would help reduce the air temperature in the bay but during recent testing I only saw a 5ēC difference with it running. As the engine air filter is mounted closer to the unpowered induction duct, positioned by the saildrive, it can be argued that this single duct should provide more than enough airflow without the need for the (noisy) fan.

So my ponderings are do we actually need to have this fan?

If we remove it we would actually have both 4in ducts available for the engine to breathe through therefore doubling the capacity of air available. It would also massively reduce noise in the cockpit making communications during mooring/anchoring much clearer.

I am considering fitting a simple on/off switch to enable us to use the fan if required instead of it being on all the time the ignition is on.

Please note that this fan is positioned high up so was never meant to be a "bilge blower" and you would not want to use it to clear any gas leak into the bilge as it is not explosion proof or intrinsically safe.

All thoughts and ideas welcomed.


Cheers

Keiron
Have you considered the ducting does not have the cross sectional area as the fan if the noise is whistling?
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Old 20-12-2015, 12:47   #15
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Re: Engine Bay extractor fan

Certainly a cockpit on/off switch would eliminate the docking communications issue but would create a risk that you forget to turn it back on. I assume there was a reason for the fan's being there. Maybe a timer off switch reversed from the usual installation, shuts fan off when switch turned and back on when timer runs out. If placed between the fan and the ignition switch this should work.
Do other owners have this issue? I would want that answer before doing much. Just a thought.
Maybe the question should be; why is this fan so noisy? In my experience fan noise can vary a lot due to both the specific fan and how installed. Have you checked the blades for accumulated crud and lubed the motor? Good luck with this one.
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