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Old 27-12-2015, 13:44   #31
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Re: Engine Bay extractor fan

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Originally Posted by hellosailor View Post
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.
I think you may have put your finger on it with an exhaust leak, not like gas that goes boom. As long as there is sufficient incoming air for the engines need. If not sufficient incoming air the engine wins.

I can recall the engineer pointing up to the funnels and saying, If they get plugged she will suck your lungs out.
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Old 27-12-2015, 22:43   #32
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Re: Engine Bay extractor fan

Valid point about ensuring exhaust fumes don't accumulate in the event of a leak, thanks for bringing that up hellosailor, that's also a good reason to have a CO detector in your cabin alongside the smoke detector.

Looking at my particular boat I'm not sure if the 4" extractor fan we have would even produce a negative pressure measurable on most equipment. We have an engine bay that "opens" along the midline and into the transom space. This means it is a huge volume of air and not just the volume directly around the engine. To create a meaningful negative pressure would require a much larger fan than we have currently.

That said I do accept the points about negative pressure, exhaust fume extraction and airflow and will add them into the equation. I think I will keep the fan for these reasons but will research a quieter version or "test drive" some form of noise suppression at the helm end of the ducting.

I will need to install a switch of some form into the circuitry due to the ignition system we have. As we don't have an ignition key and since installing the new ProSplitR the fan runs as soon as we activate the electrics to the engine (it used to be connected to the diode so only ran if the alternator was spinning). This means the fan runs without the engine even if the engine is switched off but is still "live". Particularly annoying when under sail after motoring out the marina.

Thanks for all the input and I will report back later on what I discover and how I get on.

Cheers

Keiron
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Old 28-12-2015, 04:22   #33
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Re: Engine Bay extractor fan

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Originally Posted by kas_1611 View Post
I will need to install a switch of some form into the circuitry due to the ignition system we have. As we don't have an ignition key and since installing the new ProSplitR the fan runs as soon as we activate the electrics to the engine (it used to be connected to the diode so only ran if the alternator was spinning). This means the fan runs without the engine even if the engine is switched off but is still "live". Particularly annoying when under sail after motoring out the marina.

Thanks for all the input and I will report back later on what I discover and how I get on.

Cheers

Keiron
I'm not sure about your model boat, but if you have a Volvo D2-series with the pushbuttons for start and stop then there is a relay-set available to be connected to the electronics box on the engine. The relay will energize together with the ignition. You need to remove one of the connectors from the engine and the cable-loom that goes with the relay goes inbetween the engine and the removed connector.
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Old 29-12-2015, 05:09   #34
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Re: Engine Bay extractor fan

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Originally Posted by aluijten View Post
I'm not sure about your model boat, but if you have a Volvo D2-series with the pushbuttons for start and stop then there is a relay-set available to be connected to the electronics box on the engine. The relay will energize together with the ignition. You need to remove one of the connectors from the engine and the cable-loom that goes with the relay goes inbetween the engine and the removed connector.
I do indeed have a VP D2-40 but have to admit I have never heard of this relay so will look into it.

The option I was thinking was to connect it as previous so the fan comes "on" with the ignition but to introduce an illuminated switch by the helm so we can turn it off when we don't want it (ie when anchoring) or when the ignition is on but the engine not running (engine standby while sailing). If I can add some kind of temperature switch into the equation that would be a bonus.

Cheers

Keiron
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Old 29-12-2015, 05:22   #35
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Re: Engine Bay extractor fan

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Originally Posted by kas_1611 View Post
I do indeed have a VP D2-40 but have to admit I have never heard of this relay so will look into it.
Keiron
It's part number 8 on the enclosed picture.

I have put a sensor (Some VDO thing for the automotive branch) in series with the Fan. It closes at 40 Degrees Celsius. When the engine stops and the ignition is switched off the fan also stops and venting the engine space when the motor is off is not really required and is very noticeable when the engine is off.
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Old 29-12-2015, 05:56   #36
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Re: Engine Bay extractor fan

I have a Yanmar engine and panel. It has a "soft" switch to turn the panel on then push the "start" button.
But when the engine is stopped, I turn the panel off since with the panel on the oil pressure alarm and blower are both running. The alarm is much louder than the blower.
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Old 29-12-2015, 06:56   #37
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Re: Engine Bay extractor fan

After years of an overly complicated system I came to the conclusion that it was not needed, because after the last bilge type fan burned out I found there was little temperature difference when running and that the only time I felt it was needed after shut down in hot weather ,so a computer fan was installed on a simple switch
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Old 29-12-2015, 09:54   #38
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Re: Engine Bay extractor fan

This is the point in the thread where someone does the math to demonstrate how much air a diesel sucks into the engine room and out the exhaust. My understanding is that it moves a lot more air than any recreational-grade blower.

Just to add one more controversy, the PO of my boat ran a blower intake hose down to a low spot in the ER for some reason. Obviously this makes sense for a gas engine, but with diesels I don't see the point. I'd want the blower removing warm air from the top of the ER. Which is where the manufacturer mounted the blower. Am I missing something or was this just another Stupid PO Trick?
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Old 29-12-2015, 10:31   #39
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Re: Engine Bay extractor fan

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This is the point in the thread where someone does the math to demonstrate how much air a diesel sucks into the engine room and out the exhaust. My understanding is that it moves a lot more air than any recreational-grade blower.
I'll bite:
Ive got a 1.5 liter diesel engine, typically running at 2000 RPM. No Turbo. So ideally that would take 2000 / 2 (4 stroke) * 1.5 liter air = 1500 liter air = 1.5 cubic meter. My 75 mm suction fan is rated at 3 cubic meter per minute (Jabsco). So those numbers disagree with your understanding.

My personal experience is that the temperature in the engine compartment stays quite a bit lower since I installed the new (radial) fan. The old one (axial) was very good in moving noise, not so much in moving air.
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Old 06-01-2016, 02:38   #40
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Re: Engine Bay extractor fan

Another important reason, and maybe the most important, to extract hot air from ER is not for the comfort of the passengers but to supply the engine with as cool air as possible. Hot air is less dense and has less oxygen. The engine will certainly still run but at high rpm maybe 3% of fuel injected is being wasted - there's enough air but not enough oxygen to extract maximum heat from the fuel.


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Old 06-01-2016, 03:23   #41
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Re: Engine Bay extractor fan

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Originally Posted by Kuan Yin View Post
Another important reason, and maybe the most important, to extract hot air from ER is not for the comfort of the passengers but to supply the engine with as cool air as possible. Hot air is less dense and has less oxygen. The engine will certainly still run but at high rpm maybe 3% of fuel injected is being wasted - there's enough air but not enough oxygen to extract maximum heat from the fuel.


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Very true, which is why most cars have their air intake as low as possible. However, as I mentioned, when the ambient air temperature is in the high 30šs (Celsius) and the "water bath" the bilge is sitting in is high 20šs there's precious little cooling of any incoming air flow. Admittedly if you are in the higher latitudes then you would have cooler air coming in so this would be a benefit but where I sail in the Adriatic any "performance" benefits would be negligible.
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Old 06-01-2016, 04:45   #42
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Re: Engine Bay extractor fan

Well, the oxygen content of air by mass is not changed by changing the temperature. The problem of hot intake air is simply that there is less of it, by mass.

And fuel will not be wasted unless you get into an overfueled situation. With a less dense air charge, you will have overfueling sooner, but only near max power, not at cruising loads.


Cooler air is better, but this is not the reason why.




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Originally Posted by Kuan Yin View Post
Another important reason, and maybe the most important, to extract hot air from ER is not for the comfort of the passengers but to supply the engine with as cool air as possible. Hot air is less dense and has less oxygen. The engine will certainly still run but at high rpm maybe 3% of fuel injected is being wasted - there's enough air but not enough oxygen to extract maximum heat from the fuel.


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Old 06-01-2016, 04:57   #43
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Engine Bay extractor fan

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Well, the oxygen content of air by mass is not changed by changing the temperature. The problem of hot intake air is simply that there is less of it, by mass.









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I concur....there is not less oxygen per unit of air....the only difference is that the air is less dense per unit of volume.
However on your average sailboat with a 4" inline extractor fan, the heat removal is mostly about the people. 1 small blower just isn't going to make a measurable difference to air density and intake temps.
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Old 15-04-2016, 11:15   #44
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Re: Engine Bay extractor fan

Decided to fit a simple, illuminated switch (for now) so we can manually turn off the fan if we need to communicate bow to stern. All I need to do now is fit it and figure out how to wire the damn thing in (I know the red wire is positive and the black is earth but there's a 3rd terminal for the illumination that I have to figure out )

Still going to look into different style of fans and the exhaust baffling along with the temperature switch. I'm also going to look at re routing the induction hose to see if it is possible to get that forward of the engine to aid in cooling the electronics. If not then I'm going to investigate fitting some form of fan system to help blow air over the alternator and just generally move the air in the engine compartment more.

Thanks for all the input in this thread so far (answers to the 3rd terminal question gratefully received )

Fair winds and following seas to all

Keiron
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Old 16-04-2016, 04:40   #45
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Re: Engine Bay extractor fan

How to Wire an Illuminated Rocker Switch
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