Engine bay fan?

[jeremyshaw]

When we bought our boat is had no engine extraction fans in the compartments (cat, 2 40HP engines). And no ventilation. But it worked fine.

However compartment air temperatures reached 60C. Whether that is acceptable to the engines (and wiring) or not it made it very uncomfortable if you wanted to go into the compartment.

I added simple extractor blowers and provided a passive source of cool air at a lower point.

The temperatures dropped to ambient.

This was switched with the engine. For me it was a well worth while action. Ideally I'd have liked to have a delay as well so the fans kept running for a while after switch-off.

 

[Spirit of Glenans]

On delivery trips between Ireland and France in November and April, I found that when coming off watch during or after a period of motoring, that the quarter berth was relatively cosy due to the heat coming off the engine. For this reason, I, for one would not be a fan of engine bay fans

 

[ChattingLil]

When we bought our boat is had no engine extraction fans in the compartments (cat, 2 40HP engines). And no ventilation. But it worked fine.

However compartment air temperatures reached 60C. Whether that is acceptable to the engines (and wiring) or not it made it very uncomfortable if you wanted to go into the compartment.

I added simple extractor blowers and provided a passive source of cool air at a lower point.

The temperatures dropped to ambient.

This was switched with the engine. For me it was a well worth while action. Ideally I'd have liked to have a delay as well so the fans kept running for a while after switch-off.

Reading this thread with renewed interest after our shake-down cruise in a new to us boat. Our engine bay is incredibly hot and we are looking at improving ventilation or installing a fan. Can you say which fan you mention here?

 

[jeremyshaw]

Our engine bay is incredibly hot and we are looking at improving ventilation or installing a fan. Can you say which fan you mention here?

I see from my logs they were Jabsco 3", 1457cfm. Rated 500 hrs. Similar in type to the one pictured in one of the previous posts. They are still functioning. I used flexible ducting (the coiled spring kind covered in plastic) to lead the air in and out. I made sure to have "extra" ducting in case of damage, and extra cable in case of need to replace the fans (not yet). I also put a big loop in the ducting so if we got pooped (they led to the sugar scoops) the water would be unlikely to get up. I got an electrician to wire them (I'm hazy on engine electrics) so they came on/off with the ignition and I see he put in 7.5amp fuses and 40amp relays.

This was in the Caribbean where the extra warmth was of course highly undesirable! Our engines were not under the berths, fortunately, but if they had been, in that climate, I would certainly have wanted to have the fans running for longer as the engines retain heat for quite a while and I don't think the fans would use much power, though you'd need to check. They were a little noisy. You could not hear them with the engine running and of course without a timer that noise would be a good reminder to turn them off if separately wired. But the noise might be something to consider with fan location if near a berth.

 

[Ammonite]

Running an extraction fan when the engine is running is pointless. Even a 1 litre engine running at 2000 revs will be sucking about 225 gallons of air per minute. A little fan will just slow the air being pulled in through the fan vent.

So either plumb the fan to vent the bilge as mentioned above, or run it after the engine has shut down to more efficiently rid the engine compartment of heat.

What you say makes sense to me so what could cause a distinct hot engine smell when a typical auxiliary diesel is running? I've noticed this on several boats and with my own Beta 20. Surely the engine should be dumping this out the exhaust? The smell is definitely coming from the engine bay and in my case I've renewed / checked all the exhaust fittings

 

[Ammonite]

What you say makes sense to me so what could cause a distinct hot engine smell when a typical auxiliary diesel is running? I've noticed this on several boats and with my own Beta 20. Surely the engine should be dumping this out the exhaust? The smell is definitely coming from the engine bay and in my case I've renewed / checked all the exhaust fittings

Thinking about this further, why do engine manufacturers frequently pipe the crankcase vent back to the inlet manifold? Surely the engine should suck these fumes up normally, assuming the air intake is in the engine bay and the engine is such an effective pump?

 

[NormanS]

The inlet air to the engine space on my boat is ducted so that cool air, sucked in by the engine, passes along the port side of the engine, where the alternator is, before being devoured by the engine.
I do have an extractor fan, which is ducted from the two enclosed battery boxes, and from the engine space.
The prime reason for the fan is to extract any hydrogen from the battery boxes, before starting the engine. This is of interest to boats with shore power, who may have been charging their batteries prior to starting. I don't have shore power, so the fan is never used, and not required.