Effects of not running an engine compartment fan?

[boatpoker]

Originally Posted by ramblinrod

The engine manufacturer specifies a certain CFM of ventilation be provided.

If the vessel manufacturer's solution was to install a blower to achieve it, the blower needs to be connected for the vessel to be compliant with the engine manufacturer's ventilation requirements and by association ;-), ABYC compliant.

My only point was, as confirmed by the standards snippet I posted is that ABYC DOES NOT require powered ventilation. If you can't grasp that I can't help you.

If you think I am wrong then please post the ABYC standard which does require it.

[leftbrainstuff]

You wont break anything by not having a ventilation fan. Most are so poorly installed, located and ducted that they move little air.

There is enough air leakage that ventilation will be occur due to convection anyway.

[BobFord]

I recently added a 'blower' to draw in cool air. This is targeted on to a 24v alternator. I had been having constant failure of the alternator and the expert theory is over-heating.Time will tell if the v.expensive installation was worth it !

[ramblinrod]

Originally Posted by boatpoker

My only point was, as confirmed by the standards snippet I posted is that ABYC DOES NOT require powered ventilation. If you can't grasp that I can't help you.

If you think I am wrong then please post the ABYC standard which does require it.

32.5.3 Combustion Air
– Ventilating provisions and openings to the machinery space provided for supplying combustion air shall accommodate at least the sum of the maximum air requirements specified by the engine manufacturer(s) for each propulsion and auxiliary engine(s) in that space.

So, if the means by which the vessel manufacturer intended to provide the required ventilation is by a powered ventilation system, to be ABYC compliant, the powered ventilation must be installed and operational. I suppose it would be possible for the vessel owner to come up with some other means of non-powered ventilation to meet the engine manufacturers ventilation requirements, but that is well beyond the scope of this discussion.

[Cheechako]

Originally Posted by ramblinrod

Just checked the Yanmar engine installation manual. There is a formula for calculating required ventilation based on engine displacement.

For a 4JHTE (75 HP) it is 4.15 m^3 / min or ~ 150 cfm

This means that a single Rule 3" electric blower (rated 135 CFM, open suction and discharge) would not be anywhere near sufficient.

The diesel engine requirements I've seen are for ventilation INTO the compartment for the engine to breathe! They specify the ability of air to get into the compartment. This should be separate from any fan system. Extractor fans do the opposite, take heated air and fumes OUT of the compartment.

[ramblinrod]

Originally Posted by leftbrainstuff

You wont break anything by not having a ventilation fan. Most are so poorly installed, located and ducted that they move little air.

There is enough air leakage that ventilation will be occur due to convection anyway.

This is incorrect.

All design criteria of the vessel is based on the machinery spaces being less than 50C.

Even on a vessel equipped with forward and aft facing 3" cowls, with no air flow over the boat (such as when at anchor on a still day, or even when motoring with an apparent wind near zero), the ventilation requirements for the engine and engine compartment will not be met, and any components within that space designed for a maximum space air temp of 50C may be at risk. Batteries certainly are, anything over 85F is bad. All wiring insulation will be based on the assumption the engine compartment is 50C or less.

IMHO, not power venting a sealed engine compartment of a freshwater cooled engine in a displacement (slow speed) vessel (that is going to be running with a coolant temp of 60C+) is just asking for trouble.

[hellosailor]

Keiron-
I wouldn't assume that a thermometer "high up on the rear wall" accurately reflects the temperatures on the engine block or the alternator. Especially if the fan is ducting air over the engine, as professionally designed systems actually do direct airflow in very specific ways, not just "the room".

And you may know that for every 10C rise in temperature, you cut the lifetime of discrete electronic components (like alternator diodes and regulators) in half.

So if your alternator was going to las 10 years, and the ambient temperature went up by 10C, it would only last 5 years. But reduce that temperature by 5C, and maybe the ten years only drops to 7 years, instead of 5.You should gain something like 40% longer life on the electronics. Not to mention, all the engine belts and hoses will age and break down more rapidly in the heat as well. (I don't have specific numbers on that.)

Belts, hoses, electronics, engine mounts too. It all suffers in heat. Which should be measured locally, not up on a bulkhead. (Different airflow, different cooling.)

I'd need a really big cheap blower to hear it over the engine noise.

[CarinaPDX]

From the Installation Manual for your Volvo-Penta D2-75:

Two main conditions must be met:
1. The engine must receive enough air (oxygen) for combustion of the fuel.
2. The engine room must be ventilated, so that the temperature can be kept down to an acceptable level.
Ventilation is also important to keep the engine’s elec- trical equipment and fuel system at a low temperature, and to ensure general cooling of the engine.
NOTE! All valid safety regulations and legal require- ments for each country must be followed. Each clas- sification society has its own regulations that must be followed when required.
The temperature of the inlet air at the air filters must not be higher than +25°C (77°F) for full power output. During sea trials the air temperature in the air filter should not exceed 20°C (36° F) above ambient tem- perature.
The temperature of the engine itself is rather high in some places. Certain separate electric components, such as charging regulators and relays, should there- fore be fitted on bulkheads or elsewhere where the temperature is relatively low.
The maximum temperature for areas where electric components are fitted is 70°C (158°F). The starter mo- tor and alternator however, have their given locations.

After this section there is a description of the calculation required to determine the volume of ventilation.

Putting the fan in the boat would have been required to meet the warranty requirements. Why it is not hooked up is anyone's guess. You should hook it up, and if it is used in cooler climates adding a thermostat will cut down on the noise. The fan I bought is a bit of overkill so I added a motor speed controller to cut it down.

Greg

[ramblinrod]

Originally Posted by Cheechako

The diesel engine requirements I've seen are for ventilation INTO the compartment for the engine to breathe! They specify the ability of air to get into the compartment. This should be separate from any fan system. Extractor fans do the opposite, take heated air and fumes OUT of the compartment.

Can't speak for all manufacturers, but suspect are similar, Yanmar specs require more air than required just to breathe, using a factor of 1.5 to 2.0 times as much.

For any amount of air in excess of what the engine naturally breathes, there has to be a differential pressure between the engine space and outside atmosphere. This can be achieved by blowing air in (frowned upon as this can create positive engine space pressure that could leak into the cabin) or sucking air out (preferred). By sucking air out, you bring fresh air in.

[Cadence]

Originally Posted by Cheechako

The diesel engine requirements I've seen are for ventilation INTO the compartment for the engine to breathe! They specify the ability of air to get into the compartment. This should be separate from any fan system. Extractor fans do the opposite, take heated air and fumes OUT of the compartment.

[Lepke]

I've been in many diesel engine rooms. None had neg pressure nor have I ever heard of anyone doing it except by not having enough vent area and starving the engine of air.
Larger engine rooms have at least 2 very large blowers, one in and one out. Partly for crew comfort and to keep heat confined to the area. If anything, a pos pressure would give more power and less fuel consumption.

[Jim Cate]

RE CO leakage into cabin: With a sealed engine compartment, there is no way to generate a positive pressure in the compartment with the engine running. Thus no worry about CO leakage, even without forced exhaust ventilation. With the engine shut down, there can be no CO generation (and diesel engines generate very little CO when running for that matter).

With an unsealed compartment (as in the vast majority of sailing vessels that I have been aboard), again the air consumed by the engine will cause air flow from the cabin into the engine compartment via all the natural passageways.

Cooling the compartment is a different issue, and extra air flow can't hurt.

In the OP's position, I'd check to see if there was 12 volts on the supply line, see which switch controls that voltage, and hook it up. The risk of "burning up your boat" is one that most of us would be willing to assume, being that the wiring appears to be original factory equipment. Then, with the fan working properly, i'd use it whenever I felt like it.

But that's just me...

Jim

[DumnMad]

Originally Posted by Cheechako

The diesel engine requirements I've seen are for ventilation INTO the compartment for the engine to breathe! They specify the ability of air to get into the compartment. This should be separate from any fan system. Extractor fans do the opposite, take heated air and fumes OUT of the compartment.

I'd say Extractor fan not very effective in cooling the engine room relative the air being drawn in by the engine. Could get too hot in there if you try to exceed hull speed in which case dropping the revs would be the way to go.

Fan is useful if you have oil spilt on the exhaust manifold or, if you have new paintwork putting off a smell. Mine doesn't draw from the bilge so no use in extraction gas which is why the boat has the gas bottles vented separately.

[Alita49DS]

No, a 3" fan would not be enough. Which is why my Jeanneau 49DS has a 4" fan which can move 6.7cuM per minute. https://www.jabscoshop.com/marine/bl...12-volt-dc.htm

There seems to be a load of hot air being talked about this subject. Pun intended. It depends on the boat.

On the 49DS the engine compartment is extremely well insulated and the tray under it is separate from the the bilge with a drain pipe that goes straight into the sump area. The fan is ignition switched and runs all the time the engine is on.

Is the fan needed. Maybe not in a cold climate but I can tell you from experience that if it fails in the Med the engine will overheat. Pretty quickly. The only solution then is to open all the hatches into the engine and as the main one is also the support for the companionway steps that is not a happy solution.

I made the same elementary error that some writing here make. I thought it was a marginal bit of kit and did not carry a spare. When it fails on a Sunday and Monday is a holiday in Spain and you are on a timetable I can tell you that I now carry a spare!

So, simple really. If your boat did not need a fan the maker would not have fitted one. If it is a relatively modern boat which has to comply with the RCD and EU regs then it is going to be engine ignition switched.

Going back to the original question, Dufour being RCD/EU compliant they put that fan there for a reason. Have a look at the wiring diagram for the boat and locate the fuse holder. Is there a fuse in it? If not then it probably takes a 1 or 2 amp one. Before putting in the fuse locate the red feed. If your boat is like mine the wires should be coded. Make it safe with a female spade connector. Then put the fuse in and check for current using a meter. If there is none then turn on the ignition and there should be voltage. Connect the feed and return to the fan. There are only two wires to the unit. Check by turning on the ignition. You will hear the fan. If you put your hand over the outlet you will be surprised at the amount of air coming out.

You have got away with it but my next suggestion would be to buy a spare.

If you read a book on diesel maintenance as, sad person that I am, I was doing the other day, you will be amazed at the roomfulls of air a modern diesel sucks in. Especially a turbo charged one. The fan gets the stuff, and the heat, out.

[transmitterdan]

Fans should never blow air INTO an engine compartment that shares airways with the crew cabin. Fans should always blow air out of the engine compartment to an outside vent. You don't want a blower to force exhaust gases into a living space. Thus an engine compartment should always have a very small negative pressure relative to the living space.