Reducing Engine Compartment Temperature (B36 2005)

[jonrarit]

Has anyone managed to reduce engine compartment temperature?

Our boat is in the Ionian with high ambient temps and I've always thought the engine compartment temp was too high. This was confirmed recently after fitting a sterling alternator to battery charger. The unit has a temperature sensor on the alternator and I noticed it was tripping out. Opening the steps & side panels and the temp drops within a few minutes & the A2B charger kicks in again.

According to the manual, it's set to trip at 100 degrees celcius !!!!

Obviously I'd like to keep the sound proofing so kind thinking of an inlet & outlet vent on the transom, with ducting and a blower into the engine compartment. Any other solutions?

jonathan

[Lyra]

Reducing the engine compartment temperature is always good (for the alternator for example), but I doubt if the temperature rises to 100C.
It rises to 100C over the sensor, which is probably enclosed within the Sterling equipment on the power component heatsink and is meant to protect them. When it reaches 100C this means that the internals of the power components are close to their limit (typically 120-150C). However this could also happen at say 60C when there is  not enough air circulation over the heatsinks.
Until you solve the air circulation of the whole compartment, if the unit is not already equipped with one, you could try adding a small fan which blows directly over the heatsinks - there is a drastic difference in heat dissipation when comparing forced air to natural convection.

I have a 2004/B36, which I assume is very similar, and I really do not see the proper way to create circulation, since proper circulation requires the air to flow by (i.e - one way). The engine compartment is open towards the lazarette  and the air intake port is under the helmsman seat. So creating a flow means pushing it into the saloon - not desirable. 
Maybe it is possible to change the flow direction by making an opening below the steps and using a fan to force the flow backwards - not sure how well this will work.
Or, maybe it is possible to spread a flexible duct (like those used for HVAC systems) from the front of the engine compartment, all the way back to the transom and fit over there a fan with flapped port  -not sure how good this will behave in following seas.

As said - don't really see the proper solution.

[jonrarit]

Thanks Lyra, I tend to agree 100 degrees C is unlikely, more like 60 I'd say (albeit the documentation says it triggers at 100 degrees). When the sensor triggers it reduces the load on the alternator

The temperature sensor is remote and mounted on the rear negative post of the alternator. The actual charger unit is underneath a saloon seat. The only airflow around the alternator is created by it's own cooling fan so realistically there's not much air movement at all

As for airflow, our's is the three cabin version so as I see it the only option would be two vents on the transom & ducting tubing into the engine compartment. If both ducts had blower fans one blowing one sucking that would create a one-way airflow

jonathan

[tiger79]

More recent boats have forced cooling. My 2014 Cruiser 37 has a fan in the top of the engine compartment, extracting hot air which is ducted to a vent on one side of the transom.  Fresh air is drawn in via a vent on the other side of the transom, the ducting leading to the bottom of the engine compartment.  The fan is a standard 100mm Rule in-line blower, although interestingly it's a 24v version, supplied with 12v - this may be to reduce noise.

[Lyra]

Jonathan - now I understand the sensor, it actually protects the alternator, which with the Sterling A2B is working at its full power output all the time so probably gets much hotter than when using its regulator .

Tiger - This looks like what I suggested as third option.
Where exactly is the output port located , and how is it protected from water entering it?

[tiger79]

Tiger - This looks like what I suggested as third option.
Where exactly is the output port located , and how is it protected from water entering it?

The inlet and outlet ducts are on opposite faces of the aperture of the swim platform.  You can see the inlet grille (rectangular stainless steel grille) on this pic.

[Salty]

On a friends B37(2001), he has vents, installed by a previous owner, either side but just outside of the companionway entrance near to the top of that area. This allows the warm engine room air to vent naturally to atmosphere, though it does come with a slight increase in engine noise into the cockpit area. Looking at my B36(2002), there was sufficient space on each side of the engine compartment between the aft cabin bulkheads and the GRP moulding to allow air to flow upwards from the engine compartment to such vents if I'd wanted to fit them. However instead I've placed a thick sheet of soundproofing right across the inside top area of the engine room, and this has significantly reduced engine noise within the cockpit area. Normally my engine compartment with just an MD2020D does not get very warm while operating in the Irish Sea area.

[Eye Candy]

Hello,
The problem is stratification in the engine room with the hottest air at the top.  A useful solution to this is to turn the engine air intake upwards so that it sucks the hot  air from as high as possible.  This has the hottest air being used by the engine first.  I havent measured it but it makes quite a difference to the air temp immediately around the engine.  Try it for a while then open the engine compartment to "sample" the hot air rushing out.  It is noticeably cooler with the intake upwards.
Cheers
Andrew

[Nigel]

But don't engines run better on cooler air?

[tiger79]

But don't engines run better on cooler air?

True, they do! But I don't think the performance different would be too significant in a yacht.

[MarkTheBike]

...apart from the hot air being less dense so the engine is running richer. Not a problem at high revs but could get a little gummy when chugging around at low revs for extended periods.

[Eye Candy]

The hotter air is less dense and so limits the maximum mass flow of air into the engine.  This will cause a reduced maximum power but only in proportion to the absolute temperature difference of the incoming air.  Cooler air will produce more power at a given revs.  It is a small effect.
Raising the air intake raises the position of the interface between the upper hot air and the lower cooler new air.  This keeps the alternator and other temperature sensitive parts in cooler air - a good thing.

Andrew
B39 2005

[Kibo]

I have a similar set up to Tiger on my 2014 Vision 46. It takes a lot of ducting running under aft cabin bunks back through the lazarette/stern locker but it shouldn't be too difficult to retro fit.

[jonrarit]

Just returned from a weeks fettling out in greece and pictures attached of our solution to reducing engine room temps.

One fan blows air across the alternator, the other extracts. Works a treat