Engine Room Fans

[Anonymous]

What is the preferred arrangement for ventilating an engine compartment - forced inlet air or forced extraction? The former could cause smells to leak into living spaces whereas the latter will avoid smells but maybe the negative pressure will reduce the engine efficiency?

It would be possible to arrange a neutral pressure system, providing a specified number of air changes per hour with zero pressure difference but that would involve two controllable fans, a pressure transducer and control electronics. Does anyone do this?

My own interest is for a 100hp turbocharged Yanmar in a fairly well-sealed engine compartment.

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[tcm]

imho best is an inward and an outward to create an ambient air flow. You won't reduce air pressure materially with a fan- it's not positive displacement, so in the same way the air rushes into the cylinders, it will rush in thru the blades if there was a real pressure difference. Air is incredibly incompressible, so when you walk into a room, exactly your volume of air walks out. It's not like cigarette smoke frinstance.

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[snowleopard]

it is possible to calculate for any given engine the required cross-sectional area of the engine room air intake. in my case the intake is taken from a grille near the top of the goalpost so as to be clear of any green water.

for most engines the air sucked into the inlet is enough to provide the required turnover of air but if you need more than that i would suggest an extractor fan to reduce risk of fumes getting into the accommodation. it must be combined with adequate-sized intake ducting or you could get performance problems. if you get black smoke from the exhaust you know you have a problem!

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[Anonymous]

>>imho best is an inward and an outward to create an ambient air flow....<<

Thanks, that was my view since we have a generator and watermaker as well as the engine, and we are aiming for the Med. Aside from ventilation when we are under way (under power) it would be nice to get the heat from the engine compartment out, once we have stopped, in the Mediterranean summer. I don't fancy all that heat 'seeping' into the saloon for hours.

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[Nauti Fox]

We used to have in and out engine driven fans,BUT the engine air intakes are in the lazerette.When under way the effect of this allowed fumes into the accomadation so I disconnected those and fitted two electric fans, both extracting onto the same ducting.No more fumes.But as I say the engine intakes are outside the engine room.
Al.

<hr width=100% size=1>No dear,the water goes in the other one.

 

[tcm]

Fans will reduce the effect of ambient air in the enginerrom from being preheated by the hot equipment (engine etc) but i don't think wd stop v much heat from being transferred to living quarters : the engine will run at pretty much same temp regardless of thhe fans, so when that lump gets hot, the heat transfer to living qrtrs starts.

Metallised faced insulation (axctuallly noise insualtion ,but works to prevent heat transf too) is worth considering on surfaces adjoining living areas. I used Marex-faced insulation from halyard.co.uk - dramatic effect on temps in cabin adjoining engineroom.

imho you will need one hell of a fan to significantly and dramatically reduce temps in the engineroom. I have this, but the fans are 240v, and i don't usem very much.

If you can vent the enginerrom by simply opening a hatch and lettting heat rise off when stopped (when heat in engine stops being cooled cos not working) that wd be good. Tho not many med boats suffer from the actual temp in the engineroom as far as i kno. I mean, it ain't a common problem.

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