Engine Bay Temperatures.

[steve_cronin]

We cruised in company with a boat from Argentina a couple of years ago.

The owners had bought the boat, disused for several years but in "as new" condition, mechanically and internally off of a swinging mooring on the River Plate.

Manolo, being himself a mechanical engineer, was intrigued that the deceased owner/builder had gone to great lengths to duct combustion air into the engine from the outside. Further investigation revealed that this had been done on the recommendation of the local Volvo dealer/mechanic who was very certain that many engine failures in that hot climate were contributed to or even caused by the intake air being far too hot as it was sucked from around a well insulated engine box. In an automotive application, combustion air, once a suitable operating level is attained, is sucked from outside the engine bay where possible and even the engine bay itself is well ventillated in comparison to a yacht's where supressing noise levels seems to take precidence.

Now I have to reveal that MY investigations both here and in Greece show some considerable support for the same idea.

I therefore intend to take the following action:-

I will extend the "below decks" ventillation trunking right up to, but NOT exclusively CONNECTED to the engine air intake. This is one aspect of Manolo's boat I didn't like. His engine air intake pipe is sealed to a duct running up a trunking inside the boxing on one side of the main hatch to a metal grill with protecting louvres. Now I know that this is a well protected position as high up as possible and that the boat is a veteran of a very long ocean passage but if it ever DID get pooped, sea water would go straight into the cylinders of the engine. My intended installation would avoid this by stopping short of the actual air filter intake.

A further adaptation would be to use the second of the vent pipes (both right aft near the gas bottle stowage if you know Bavarias) to supply cool air to the other side of the engine in the vicinity of the alternator to keep that cool when it is running in "boost" via the Sterling controller.

Anyway, probably of no relevance to UK owners, but to those in the tropics and the Med. I hope that this is of interest.

Steve Cronin

 

[rogerthebodger]

Generaly the cooler the intake air to an IC engine gives better (higher) power.

On my new yacht I will be ducting air to the intake of the engine direct from outside

1) to gibe better power output as above but also to allow me to "seal" the engine compartment to reduce the noise from the engine. I am also ducting air out from the engine compartment to reduce the temperature inside to reduce the heat inside the boat.

 

[steve_cronin]

Yes, that latter point of ducting air out will be even more important once the combustion air is remotely introduced since engine bay air will no longer be evacuated by being inducted into the engine so it will just cause a build-up of internal boat temperature.

Steve Cronin

 

[pvb]

Good idea...

It's a good idea to try to duct outside air into the engine compartment. My HR352 has a duct to take cool combustion air from the cockpit to a position close to the alternator - and I think this duct was a standard-fit item.

 

[FullCircle]

My Jeanneau Sun Odyssey 35 has this system as standard.
The duct intake (cover) is high up on the transom with a 4 inch spiral bound hose. This loops up for anti siphon of ingested intake water if any. This is led forward into the engine compartment and finishes quite high in the compartment, just level with the front of the engine (Yanmar 3YM30) and the air intake is the standard filter toward the right hand side rear of the engine.
In addition there is a return duct which follows a similar routs back out to the transom on the opposite side see the picture here.

There is a temperature sensor strapped across the air exit pipe which operates a small fan in the exit side of the system which drags the air through from the outside. It operates in about 23-25 degrees C when I am constantly over 2750RPM cruise. You can hear it cutting in and out, but its not intrusive.
You can see the hose in the pic with the sensor. The other hose was tucked up out of the way for clarity in this pic.



This does allow the sound proofing and gap sealing to be very good, which is why the boat is so quiet under engine.

 

[jeremyshaw]

Personally I'd concentrate on sucking the air out rather than pushing it in.

Our boat (a cat in the Caribbean) had totally unventilated engine compartments. Frankly I was surprised it worked at all. It certainly got very hot (60C!) which can't be good for the wiring let alone the efficiency. It also made working in the compartments under way horrible. I put in blowers to get the air out, and passive ducting to allow air in at an opposite point. I reasoned that if I did get any water trying to get up my ventilation system I would rather it was blown out than sucked in.... Can't say whether it's improved the efficiency, but it has certainly made those compartments a whole lot cooler.

 

[wingdiver]

Hi
Our air intake comes from a louved thingy on the outside of the pilothouse at deck level. The air filter unit (huge!) has a water trap/release point at the front end so any water that comes in that way is dumped into the bilge. We also have a large extractor fan to pull hot air out of the engine bay.
If a piccie or two and details of the kit would assist, let me know and I'll do my best.
D

 

[silver-fox]

I don't speak from any great knowledge here - but as usual that is not going to stop me!

When we were boat buying we looked at a boat, with forced ventilation to the engine compartment installed for exactly the same reasons as Steve has already described.

As I bought that model of boat, but not the one with the ventilation I did give the matter some thought. I concluded (rightly or wrongly!) that it was unnecessary because once the engine is running the amount of air being drawn into the air intake is sufficient to ventilate the engine room.

For example a 2 litre four stroke diesel will use roughly 1 litre of air per revolution. If the engine is running at 2000 rpm then it will draw 2000 litres of air into and through the engine compartment each minute.

I would have thought this would refresh the air in the engine compartment with enough frequency to stop any air consumed by the engine being of a significantly higher than the ambient temperature.

Or have I missed the point?

Once the engine has stopped then there would be a heat build up and that might cause the cabin to be more uncomfortable, but if I understood Steve correctly he was more concerned about engine performance.

 

[Guest]

Why bring in salt laden air to an alternator or engine input?

Yes, engine air temperatures are important but so is corrosion. A running engine is a very large air pump. So as long as you can supply enough that the box is not at a too lower pressure, do not worry.

If you are concerned just add an intercooler off the sea water. Stainless tube radiator would do. We pull the air from the dry bilges which is cooled by the ocean.

Our engine moves about 3 m3 of air a minute. Which is equivalent of 3 shower extractor fans. You need serious extractor systems to make any real difference.

 

[Piddy]

I choose to extract hot air from the engine bay using a blower - as the compartment isn't sealed there is a plentiful supply of air to it including ducting from the cavernous cockpit locker.
However, I have a timer that runs the fan on for 40 minutes after the engine has been stopped dissapating any heat build up while the engine cools down (a bit). This seems to work well with the benefit of exhausting any hot engine smells ouside.

Cheers

 

[Chris_Robb]

Steve - wont the ducking direct to the enging intake stop the air circulation to the rest of the compartment? ie by doiing this, you will get less fresh air drawn in to areas like the alternator. An engine moves huge volumes of air, so I doubt whether small fans would have much effect at all.

I was thinking about your earlier post to my Sterling one, which made me think that I would have to improve the ventilation to my alternator, now its actually doing some work. I was going to take a ducking from the sail locker - along side the engine room, and run it to just above the alternator. But then I got to wondering where the air comes from, as the engine compantment is totally sealed above the floorboardsm, so I suppose most of the air is drawn from the blges, and therefore it wont drag much air in from the sail locker.

We will be moving to the Med by 2009, so I suppose I need to think of these things.

Chris

 

[boatmike]

Steve, you are moving towards a "standard" installation that would normally be found in larger vessels. I think you are fundamentally on the right track but to do the job properly the following tips might be useful.
1. Don't pressurise the engine room with an input fan. Rather use an extractor fan to remove stale air. This does not need to be a huge beast if you get your duct sizing right as it is only there to ensure no dead air remains and there are no "hot spots". Ideally it should have a fully enclosed "spark free" motor though.
2. make sure the cross sectional area of the intakes are about twice that of the extractor vent. Otherwise the engine will "eat" all the air coming in and there will be no circulation of air in the engine room.
3. Try to make the extract air vent as far away as you can from the intakes. and away from the engine air intake (usually in forward out aft works best but if its a small compartment extract on the other side of the engine to the air intake.
4. Remember the poor old alternator needs to be kept cool too. not a bad plan to have one of the air intakes (or the air intake if there is only one) near the alternator. (below it is best to avoid directing damp salt air directly at it)
5. Site the air intakes away from the cockpit if you can as they will transmit noise. If you can, fit dorades over them to prevent water ingress.
6. Depending upon the design of the boat keep all engine room intakes and exhaust trunking as high as you can to minimise the risk of downflooding. Never have intakes in a position where a freak wave can cause them to be underwater (like into the cockpit!)
7. It is an excellent idea to be able to run the extractor fan for a minute or so before you start your engine especially if batteries are in the engine room to purge any gasses/fumes before hitting the start button....
Hope this helps
Good luck, your engine will thank you for looking after it!

 

[boatmike]

Didn't read your post before replying directly to Steve's but this looks to be a good compromise solution considering the size of the boat where the "ideal" installation is often impractical. I like the temperature sensor on the fan (apart from it being something else to go wrong!) but would be inclined to fit an override switch to enable the extractor fan to be run before starting the engine to clear fumes, especially if you have batteries in the engine compartment. Good stuff though, especially from Bavaria that often get a lot of stick for cutting corners to save pennies. Most designs have no engine room ventilation at all other than leaving a vent for the engine to breathe......

 

[steve_cronin]

No fans to be used at all.

Just natural aspiration. Ventillation, is, I think the key, not forced draught. Even the current "Hot spot" above the engine will benefit from that. We currently have a wooden clothes drying rack over the engine. Works a treat although the humidity is attacking the glossy surface of the sound deadening.

Steve Cronin

 

[oldsaltoz]

Interesting that no one has highlighted the huge amount of heat generated by hot fuel being returned to the fuel tanks, has anyone looked into this?

We run twin 2003 Volvo's with sail drives, one in each hull (cat) and they have a bulkhead fore and aft of them, you can walk right around them so working on them is a breeze, the fuel tanks are above the engines under the cockpit side seats. this arrangement ensures there is no chance of any diesel smell on board.

Ventilation is a simple 8 inch duct connected to a dorade vent on deck the bottom of the duct sits very close to the bottom of the hull and is just open ended.

The theory is that cooler air from outside is allowed to flow around the lower area of the compartment then drawn into the engine intake as it warms and rises.

Seems to work very well without any fans or other ventilation, both engines are raw water cooled and I suspect this may make some difference. The extra plumbing and assosiated hot rubber, steel or plastic for heat exchangers etc would have to generate some extra heat if fitted.

We often have had both engines running at 2800 RPM for 18+ plus hours and you can put your hand on the block, it feels warm but will not hurt you. Needless to say the alternators are a lot warmer but they have never been repaired or replaced in the last 5 or so years, and she gets used a lot more than most other boats in the marina. Most weekends and at least a couple of times during the week, even if it's just a twilight sail for no reason at all.

Avagoodweekend......

 

[thalassa]

Ducting directly from outside to carburettors is a standard feature on older racing and rally cars. Example: Sebring MGB's.
Our now 25 year old Dufour 2800 use to have separate ducting installed from new, from an intake outside the boat, to the intake manifold.
The principle being, colder air in > more horsepower...

 

[boatmike]

Re: No fans to be used at all.

Well it's you choice Steve but for the price of a little fan you could have an installation like that on Full Circles boat. I think in most temperate climes it is possible to get away without a fan but in a hot climate I would certainly fit one for peace of mind. I think the engine will naturally suck air in from outside anyway but will certainly run better if that air is as cool as possible and not drawn from a hot engine compartment. The real risks though are the alternator (most fail due to overheating) and batteries. If you don't have batteries in the engine compartment (which is not really a good idea anyway) you can probably live without a fan. If the batteries are in there too I would not go to sea without forced ventilation. I tend to go over the top a bit as I have spent most of my life designing and building larger installations for commercial craft subject to Lloyds or DNV approval and MCA requirements for passenger craft but the same principles apply however big it is. You can buy a suitable fan for a few measley quid and the current it draws is insignificant as it only runs when your engine is working. Why not fit one?

 

[Guest]

[ QUOTE ]
We cruised in company with a boat from Argentina a couple of years ago.

The owners had bought the boat, disused for several years but in "as new" condition, mechanically and internally off of a swinging mooring on the River Plate.

Manolo, being himself a mechanical engineer, was intrigued that the deceased owner/builder had gone to great lengths to duct combustion air into the engine from the outside. Further investigation revealed that this had been done on the recommendation of the local Volvo dealer/mechanic who was very certain that many engine failures in that hot climate were contributed to or even caused by the intake air being far too hot as it was sucked from around a well insulated engine box. In an automotive application, combustion air, once a suitable operating level is attained, is sucked from outside the engine bay where possible and even the engine bay itself is well ventillated in comparison to a yacht's where supressing noise levels seems to take precidence.

Now I have to reveal that MY investigations both here and in Greece show some considerable support for the same idea.

I therefore intend to take the following action:-

I will extend the "below decks" ventillation trunking right up to, but NOT exclusively CONNECTED to the engine air intake. This is one aspect of Manolo's boat I didn't like. His engine air intake pipe is sealed to a duct running up a trunking inside the boxing on one side of the main hatch to a metal grill with protecting louvres. Now I know that this is a well protected position as high up as possible and that the boat is a veteran of a very long ocean passage but if it ever DID get pooped, sea water would go straight into the cylinders of the engine. My intended installation would avoid this by stopping short of the actual air filter intake.

A further adaptation would be to use the second of the vent pipes (both right aft near the gas bottle stowage if you know Bavarias) to supply cool air to the other side of the engine in the vicinity of the alternator to keep that cool when it is running in "boost" via the Sterling controller.

Anyway, probably of no relevance to UK owners, but to those in the tropics and the Med. I hope that this is of interest.

Steve Cronin

[/ QUOTE ]

I know a ship and a yacht are two different beats ... but I can pass this one on ...

A RoRo ship that I was on from Miami to Central America .. was an ex North Sea job. We could not run engines at full speed because of the lack of cool air into the engine room ... so a) engine speed was restricted, b) extra forced fan feed was fitted. It was not only temperature but also the huge amount of air a diesel consumes when running ...

 

[fireball]

I'm in the process of fitting an extractor fan to the ventilation pipe in the engine compartment - we were not so bothered about the heat, but more to do with the smell as the engine compartment is not gas sealed from the aft cabin or bilges we get quite an engine smell .... with the extractor the smells are largely pumped overboard .. does that make us a stinkpot?!

 

[steve_cronin]

Re: No fans to be used at all.

Batteries under the saloon dinette in line with the keel - best place IMO, in the middle of the boat.

Yes for the alternator vent I might fit a fan but the combustion air supply will be served by a simple length of 100mm ducting terminating near to but not connected to the engine air intake.

Steve Cronin