Engine Bay Extractor Fan - 35' Yacht

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VicMallows

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Engine Bay Extractor Fan - 35\' Yacht

Could the panel kindly advise me on the precise purpose and general use of an engine bay extractor fan on a typical yacht (35ft; Yanmar 3GM diesel). I have not had experience of these up till now.

Specifically:

Am I correct in assuming that the primary purpose is to remove engine fumes which might otherwise infiltrate the accomodation?

Is it usual for the extractor to run whenever the engine is running, or does it only cut in when the engine gets particularly hot? Or is it switched on (manually) when the engine is about to be switched off so as to vent the fumes which will no longer be drawn into the engine and consumed......then switched off after all fumes have cleared?

I understand that should an engine fire occure, sucking air through the engine bay is not a good idea and so an 'EMERGENCY OFF' facillity is required. How is this usually implemented?

Many thanks for all advice, Vic
 
Re: Engine Bay Extractor Fan - 35\' Yacht

Hi vic, well I have two jabsco fans in my engine room one that blows cold air on to my turbo air filter and alternators and one to take hot air out and I only use them when I have been under power for a few hours to change the air so to speak in the winter months but in the summer I use them more and they are both on a manual switch as even though they are not noisy I don’t want or need them on all the time.
 
Re: Engine Bay Extractor Fan - 35\' Yacht

[ QUOTE ]
Am I correct in assuming that the primary purpose is to remove engine fumes which might otherwise infiltrate the accomodation?

Will also remove Gas from the area.

Is it usual for the extractor to run whenever the engine is running

Should be run prior to starting to remove fumes and possible gas.

does it only cut in when the engine gets particularly hot?

Only if a sensor is fitted.

Or is it switched on (manually) when the engine is about to be switched off so as to vent the fumes which will no longer be drawn into the engine and consumed, then switched off after all fumes have cleared?

Common in sailing craft.

I understand that should an engine fire occure, sucking air through the engine bay is not a good idea and so an 'EMERGENCY OFF' facillity is required. How is this usually implemented?

Thermal sensor installed with alarm attached.

Hope this helps.

Avagoodweekend......
 
Re: Engine Bay Extractor Fan - 35\' Yacht

beneteau fit a big inlet pipe from the transom area to the intake area of the engine, this to ensure cold dense air for the engine, there is also a similar sizes one with an extractor fan that runs continuously to exhaust hot air that rises from the engine to the top of the engine compartment. so cold air in, hot air out, cold dense air means more power from the engine, thats why they have intercoolers on turbo charged engines.
stu
 
Re: Engine Bay Extractor Fan - 35\' Yacht

Both our engines (sail drives) have bulkheads fore and aft, each is fed fresh cool air from a dorade vent on deck via an 8 inch flexible duct that flows to the bottom of the compartment, rising hot air is drawn out by another vent aft.

This setup means no fumes ever get into the cabins or saloon and was a major factor in our selection criteria when purchasing, it also provided full and easy access to any part of the engine/s.

A running engine will leave little air in a compartment that is not consumed in very short period of time, however, whilst removing hot air will improve performance, it's the cooler air contaminated with heavier gases that cause the smells on board, a small air duct that will pull some air from the low area via blower or extraction fan will reduce the problem considerably.

Hope this helps.

Avagoodweekend......
 
Re: Engine Bay Extractor Fan - 35\' Yacht

Hi Vic,

Not quite what you were asking, but here's my modification that you might find interesting.

On a Sadler 34 the batteries are surrounded by insulation on five sides and have the bunk cushions on top. On long motoring passages they can get quite warm and have even boiled once. I added a fan to blow air into the bottom of the box from the saloon and out through a number of holes drilled into the engine bay. You can just see three, about 30 mm diameter. The fan is wired into the engine circuit, comes on whenever the engine is running. The batteries are separated by strips of wood to ensure that air passes between them. The modification seems to have helped.

Batteryboxfan.jpg


Regards, Vyv
 
Re: Engine Bay Extractor Fan - 35\' Yacht

The fan on my L33 is connected to both the engine ignition key and fire suppression system. It also has a manual override switch so you don’t have to have it running if you don’t want.

Basically if the manual switch is on it runs when the engine does unless the automatic fire extinguisher is fired when it will stop automatically.

Steve
 
Re: Engine Bay Extractor Fan - 35\' Yacht

I find the extractor fan is essential in hot weather to cool down the engine compartment.
When the engine is running I expect all the hot air gets sucked into engine air inlet but when it stops , that great lump of metal just sits there radiating kilowatts of heat. Unless you want the boat to heat up ,switch on the extractor fan.
 
Re: Engine Bay Extractor Fan - 35\' Yacht

We usually motor with ours running and it was highly useful when our cooling water failed. The Vetus water trap melted and engine exhaust smoke went into the engine compartment which then went out via the fan. We saw the smoke blowing out the side of the boat before the engine overheat alarm went off! Now have water flow and exhaust temp alarms after this do.
 
Re: Engine Bay Extractor Fan - 35\' Yacht

I agree that the resistance of the batteries may well have been high, as they were a long way from being new. However, once cooled down they were perfectly OK and we kept them in service for another three years. Since then I have regularly monitored battery temperature when under engine for prolonged periods, and it seems that the fully insulated battery box on the Sadler allows any charging heat to accumulate, as it has nowhere to go. The blown air cooling that I now use has improved the situation considerably.
 
Re: Engine Bay Extractor Fan - 35\' Yacht

Vic,
Hi Vic
You're welcome to have a look at the engine compartment fan arrangement on our boat next time we're both down in Emsworth- Fitting out Supper 29/03/08 or give me a bell? That's if you haven't sorted it by now?
Cheers
Dick
 
Re: Engine Bay Extractor Fan - 35\' Yacht - Thanks

Many thanks for all the input. I think I have concluded the ideal arrangement would be an ignition wired extractor which comes on by a thermostat when engine bay temp rises; has a delay timer (like a bathroom fan) to keep it running for some time after the engine is switched off; a manual-off facility, ideally one which resets when engine is next started; and an automatic off in the event of a fire.

Vic
 
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