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Old 20-12-2015, 13:34   #16
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Re: Engine Bay extractor fan

Our 1998 Beneteau 36 had a blower fitted, not sure if by the builder or the first and previous owner. Regardless of who fitted it the PO included it on his list of stuff to snitch before final handover to us ( actually to the delivery crew, we were not presentwhich was plainly stupid in hindsight). The engine runs just fine with two 4 inch hoses venting or drawing in air via 2 clam shell fittings on the transom/swim platform. It is quiet and we smell nothing in the cockpit unless the full fitted cockpit canopy is up with a side/back panel open and the wind blows some exhaust fumes in.
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Old 20-12-2015, 15:44   #17
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Re: Engine Bay extractor fan

In answer to some of the points mentioned:

Fan is brand new, fitted last spring to replace the one that failed.

Noise is acceptable at the helm, more a loud hum than a roar, but it is noticeably easier to communicate from bow to helm with out it

Temperature difference in engine bay (measured with electronic thermoprobe) is around 5ºC. 45C with and 40C without the fan.

Fan (4in dia) blows from engine bay to outside along a substantial length of 4in dia ducting. You can feel the heat at the helm but barely any flow.


My gut instinct is it is there for a reason, what that is I have no idea If I can get away without having to rewire it or run it constantly then it will be a huge bonus but if there is a significant reason for running it then so be it, I'll wire it in and accept the humming.
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Old 20-12-2015, 16:09   #18
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Re: Engine Bay extractor fan

Quote:
Originally Posted by GordMay View Post
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
Gord,

That link works so thanks for that. A quick read and it does look more geared towards the 1000hp plus engines found in motor cruisers or super yachts but I can see how some of it does translate down to my 40hp unit. Cooler air does boost performance which is why my 1971 Mini had the air intake in the wheel bay. However when the induction air temp is 35C one does have to wonder what benefit you gain? If the induction ducting was "bilge cooled" or I were in a cooler environment I could see the benefit but last year the Adriatic hit 30C and air temps were in the low 40's for part of the summer. Given the temperature in the engine bay never exceeded 50C and only reduced by 5C when the fan was running for over 2 hrs I'm inclined to think it is more effort that is worth it.

I can see the possible benefit of slight negative pressure in the engine bay meaning no (or less) leakage of heat and odour into the cabin but with my engine bay panels sealing very well I'm not convinced there is a huge difference.

The only area I can see a benefit is keeping the electronic components cooler. If you can keep the alternator, voltage splitter and other electronics cooler then they will last much longer. That said one would expect components designed to be installed in an engine bay to work in engine bay temperatures. Most electronics I have worked with in my time are rated to 40C and it is only extreme variants that are rated to higher (I've installed sensors rated for 70C), even then the 40C ones worked fine at above that as long as it was not for excessive periods (ie constantly).

I'm almost wondering if it is actually worth running the induction hose as far forward into the engine bay as possible and fitting the fan to it so that it draws "cooler" air in front of the engine, possibly below the alternator, to utilise the "cooler" air in this way.

Cheers

Keiron
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Old 21-12-2015, 01:31   #19
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Re: Engine Bay extractor fan

Interesting discussion. I agree that the noise may be a fan issue - most 12 volt fans are not that noisy. As diesel engines consume much more air per unit power than gasoline engines, I consider the fans are essential.
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Old 21-12-2015, 02:14   #20
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Re: Engine Bay extractor fan

Keiron. I've got a set-up just as you described, discharges into the cockpit. I just turn it on occasionally. I don't think its really neccessary now I've had the injectors done and most often run the engine at a quiet 1100 or 1200 revs.
Previously I'd run the 6 cyl Ford engine at 1600 revs & the fan was effective in reducing engine smell in the saloon.
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Old 21-12-2015, 04:19   #21
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Re: Engine Bay extractor fan

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Originally Posted by kas_1611 View Post
My gut instinct is it is there for a reason, what that is I have no idea If I can get away without having to rewire it or run it constantly then it will be a huge bonus but if there is a significant reason for running it then so be it, I'll wire it in and accept the humming.
On my (CE-marked) boat I have a extraction fan as well. However it only starts running when the temperature at the engine bay exceeds 40 Deg. C and if the ignition is switched on.
So effectively it only runs when the engine itself runs as well, that makes the fan hardly noticeable. I did replace the in-line blower for a radial model. Those are typically much more quiet. They also give better performance.
In our case the engine-bay temperature dropped considerably (did not measure it).
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Old 21-12-2015, 04:31   #22
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Re: Engine Bay extractor fan

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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 5ºC 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


There is a lot of confusion regarding Combustion air requirements and machinary space ventilation. Your engine must be provided adequate combustion air, at full revs. The heat generated by the engine also needs to be removed, and that is the purpose of the extract fan. These sometime wrongley get referred to as bilge blowers. Typically they are located as high as possible (with a diesel) , since heat rises, and the intake combustion air enters lower, so avoiding short circulation. As you recognise all motors should be intrisically sealed. Extract rate is approx the same as combustion requirements, although this may increase in warmer climates. Petrol engines have a reverse arrangement , since the volotiles tend to sink lower, so requiring a blower or lower, or additional take off for the extract. There are simply rules of thumb, but if you wer building you really need an accurate formulea. have a look at Vetus for some simple guides.
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Old 21-12-2015, 05:30   #23
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Re: Engine Bay extractor fan

Greetings and welcome aboard the CF, Cmdr Bond.
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Old 21-12-2015, 05:54   #24
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Re: Engine Bay extractor fan

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Originally Posted by aluijten View Post
On my (CE-marked) boat I have a extraction fan as well. However it only starts running when the temperature at the engine bay exceeds 40 Deg. C and if the ignition is switched on.
So effectively it only runs when the engine itself runs as well, that makes the fan hardly noticeable. I did replace the in-line blower for a radial model. Those are typically much more quiet. They also give better performance.
In our case the engine-bay temperature dropped considerably (did not measure it).
Now I like the sound of this system. Where did you get it from or was it factory fitted? Where did you get the radial fan from as I'd love to be able to reduce the fan noise.
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Old 21-12-2015, 06:23   #25
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Re: Engine Bay extractor fan

There is a very good article on this subject from David Pascoe here.
Marine Engines: Sail Boat Auxiliaries at Dockside Reports

I have followed his advise and installed a " Delta T Systems " continuous duty 12v 4" blower in my engine room that runs while my main engine is on. It extracts the very hot air surrounding the engine to a Vetus mushroom vent aft, and creates a vacuum that draws fresh air in from a cabin top dorade. One of the main problems with most blower motors are they are cheap rubbish that make a lot of noise and push very little air before dying a slow death. Delta T makes very good blowers, mostly for larger applications in motoryacht engine rooms but their smallest unit will work for most sailboat applications.
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Old 21-12-2015, 06:59   #26
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Re: Engine Bay extractor fan

my boat does not have a engine copartment exhaust, and I have noted several others do not have them as well, I have checked and was told that the builders only installed them on gas engines, not sure how ture this is
i have not had any issue with overheating
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Old 27-12-2015, 09:57   #27
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Re: Engine Bay extractor fan

my Beneteau 373with the 3JH4 Yanmar had an inline blower 3" did out with 2 3"did input ducts, all at the stern.
My Jeanneau 409 has a squirrel cage blower installed at top of engine compartment with a 3" duct exiting out the stern. The intake ducts are two 3" located at bottom of the engine compartment bring in air from the stern at other side. the engine is the same, 3JH5. One can feel the heat exiting with a low level low pitched sound although lower the the engine sound level.
They are factory installations.
Recently the fan was noisy so I was given a new one under factory warranty but it came as the same rating but physically different such that it was not a "drop in". I filed the plastic fan shroud down the fix the noise.
So I have a spare now. It is for sale though.
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Old 27-12-2015, 10:45   #28
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Re: Engine Bay extractor fan

I think it's function is to keep heat and maybe smells out of the boat. On a warm day if we have been motoring it is noticeably warmer in the boat after we shut the engine down.
What would seem logical would be a thermostatically controlled fan that would run above the set point, regardless of the ignition.
I bet it would run for hours too as it takes awhile for that. Engine to cool.

Squirrel cafe blowers are orders of magnitude quieter, and you pay more for them too. My current blower is a round bilge blower and I will replace it with a squirrel cafe blower eventually. If the thing didn't come on with the ignition, I'd never know if it didn't work, because I can't hear mine over the engine noise.


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Old 27-12-2015, 11:38   #29
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Re: Engine Bay extractor fan

The blower extractor for the engine compartment on Shiva is on when the key switch is on the first position. This energizes the engine instruments as well. Turn the switch to position 2 and it energizes the solenoid which turns the starter and fires up the engine. Instruments and blower of course remain ON. The blower is not heard consider the noise level of the engine.... but it IS heard in position 1... and will drawn air from the engine compartment. It removes heat and odor. Seems like a good idea.
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Old 27-12-2015, 13:19   #30
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Re: Engine Bay extractor fan

Keiron-
That slight negative pressure would also ensure that if your exhaust system has a leak, any fumes or monoxide produced would be sucked out, rather than possibly accumulating below with fatal results, not just unpleasant ones.
Since your fan was replaced, it is very possible that you can buy a much quieter one, if you do some exploring online. The primary manufacturers of "muffin" fans include companies like Rotron, who used to list about four pages of different fans in "simple" sizes like 4 inches. There is actually quite an esoteric art to designing fan blades that are durable, strong, quiet, and move a lot of air, and quite a large variation in the performance and cost of what you and I would say "looks the same!" fan blades.
Rotron also used to list the noise level (in decibels) along with the volume of air moved at a standard speed for each fan. So, if you know the volume of air you are required to move? You look for the lowest noise level for a fan of that size. If you can't afford it, you'll find cheaper ones are always noisier, or have a blade design that moves less air, or have a motor with a lower life rating.
But there are guaranteed to be options for this, from multiple sources, and it is always terribly unlikely that a fan which was bought "because it has to be 4 inches" is going to be the best choice for other needs.
For instance, the fans used in computer server racks? Are chosen because they move the most air with the longest service intervals. Noise levels? No one cares about noise, they run in unattended rooms! In a home or office computer? You'd never tolerate one.
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