Engine bay fan?

[wotayottie]

Interesting. See my alternator thread - I suspect my alternator is overheating so what do I do?

 

[Cardo]

Thanks for the abuse. This thread is about small, inboard diesels. It's the PBO forum. The specific inquiry was about an engine box with a small extraction fan mounted to its upper end. In all probability it has a water cooled exhaust system.

I am not sure where Tim gets his idea that this is about small diesel engines. If the OPs engine is petrol then it is most likely an extractor fan as already said to get rid of fumes in the bilge. It is quite likely that the ducting from the fan to the bilge has been lost. This extractor can be a vital safety feature to remove combustible gases that might builds up especially if the petrol engine is hard to start and is flooded. The fan is run prior to engine start and switched off once the engine starts.
If indeed it is a small diesel then it surely is an attempt to cool a shut down engine and possibly stop heat drifting into cabin. good luck olewill

The engine's a 35hp inboard diesel. It isn't the original engine, but it's not far from the original's spec.
There was no ducting to the bilge. The fan's inlet in the engine bay is intact.

Unless the engine installation has been specifically designed to rely on air being blown INTO the bay (which on a saily boat is highly unlikely) the fan will be an extract one.

As you have the intake at the top of the bay, it has been designed as a heat extraction one, and will not be need to be an explosion proof one, unless you feel very risk averse.

If the intake were at the bottom of the bay, then there is more of a chance that hydrocarbon gases MIGHT be sucked up past the fan; in which case you do need a non-sparking fan.


As indicated in other posts, run it for a few minutes after stopping the engine to get rid of heat and perhaps some fumes.

I'm fairly certain the purpose of the fan is for heat extraction. Whether I should run it whilst the engine is running is my concern. It seems it wouldn't make much of a difference?

 

[sarabande]

I cannot see any small diesel engine needing a heat extraction fan while under way; the amount of air drawn in when running is quite enormous, as our techy discussion on this thread is revealing

There MAY be areas of the exhaust/alternator that become warm, even hot, during prolonged operation, but you will already know if that is the case.


My guess is that it is a 'normal' extraction fan, to be used to help remove some hot air and smells from the engine bay after use. 5 perhaps 10 minutes after stopping, if you can afford the battery drain, will help the cooling down process, and take away some enginy smells, but there are an awful lot of therms in a big engine block.



BTW. Picket boat ? With the Kitchen rudder - happy memories

 

[peteK]

Our little boat has been fitted with an engine bay fan since she was new back in 1979. I've discovered from reading the original paperwork that it was an optional extra specced by the first owner.
The fan is one of those blower jobbies that sucks air out of the engine bay and out through a vent on the topsides. However, it only comes on when I manually switch it on.

Question: What's its purpose? Should I turn it on when we're motoring? Should it ideally come on above certain temperatures? Should I fit some sort of thermostat?

I thought engine bay fans were from the days when small boats used petrol inboards(to extract fumes before starting).

 

[TimBennet]

I am not sure where Tim gets his idea that this is about small diesel engines.

The OP claims (in his profile) to own a small Southerly. I'm trying to answer relevant to this and to put aside petrol engines, picket boats, tugs, oil rig generator rooms, steam engines, etc!

 

[Colvic Watson]

It doesn't do any harm to run it when the engine is on, it just doesn't do any good. It's so puny compared to the air intake - which by the way will usually be at the top of the engine so extracting the hottest air. It is jolly useful after engine shut down.

 

[Piddy]

I run a smallish (but a bit noisy) fan to extract air from the engine compartment with my 30hp Thornycroft.
It outputs warm air even in the winter and hot air in the summer and keeps the engine fumes out of the boat. I have no leaks (oil or water) but there always seemed to be an engine 'smell' when running that the fan has cured completely.
It runs on for 40 mins after the engine has been turned off and is 'switch-offable' from the engine panel in the cockpit.

The engine bay is open to the bilge (as Moodys' built them in 1988) so it helps exhaust any bilge smells.

Works for rme!

 

[temptress]

Our little boat has been fitted with an engine bay fan since she was new back in 1979. I've discovered from reading the original paperwork that it was an optional extra specced by the first owner.
The fan is one of those blower jobbies that sucks air out of the engine bay and out through a vent on the topsides. However, it only comes on when I manually switch it on.

Question: What's its purpose? Should I turn it on when we're motoring? Should it ideally come on above certain temperatures? Should I fit some sort of thermostat?

So we have an engine bay fan. The engine is a 69hp yanmar. The fan is recommended by yanmar and used to have a thermostat. When this failed we noticed a reduction in the engine performance and a slight increase in fuel consumption. I contacted yanmar and they strongly recommended fitting a new fan that is wired to the ignition switch.

The new fan comes on when we switch the engine on and stops when we switch off the ignition.

We have vents/pipes to draw air into the engine bay directly from outside and the blower vents it's air directly outside also. All recommend by yanmar as best practice.

We live on board and have had this setup in cold Northern winters, and Med Summers and the CARRIBEAN. Where possible I would recommend following the manufacturer best practice recommendations. Will the engine work without? Yes of course it will but I think following the instructions is often a good idea.

 

[30boat]

Say what you will an engine fan is important.The temperature inside my engine compartment is much lower when the fan is on,whis is all the time the engine is running,and the added bonus is that there are no engine smells and the cabin is markedly cooler .

 

[West Coast]

Interesting. See my alternator thread - I suspect my alternator is overheating so what do I do?

If I have got this right, you and I have the same boat (starlight 35) but different engines (me VP 2003 and you I would guess VP 2030). But in both cases the engine box is small and well sealed, and the engine space gets very hot. This past winter, I enlarged the box very slightly (35mm longer, 30mm higher) which allows much better airflow round the engine. I also installed a blower which is normally set to run for a short time after the engine is switched off, extracting air from the engine compartment and out through a cowl on the stern.

While I have not had the same alternator problem as you, I can understand why an overheat problem could be your issue

Another thought - my VP unit is a saildrive, I am sure it helps as a heat sink!

 

[Tranona]

If I have got this right, you and I have the same boat (starlight 35) but different engines (me VP 2003 and you I would guess VP 2030). But in both cases the engine box is small and well sealed, and the engine space gets very hot. This past winter, I enlarged the box very slightly (35mm longer, 30mm higher) which allows much better airflow round the engine. I also installed a blower which is normally set to run for a short time after the engine is switched off, extracting air from the engine compartment and out through a cowl on the stern.

While I have not had the same alternator problem as you, I can understand why an overheat problem could be your issue

What you are saying is very relevant to this discussion. Looked at an engine installation on a Starlight like yours and was amazed at how the 2030 was shoehorned into such a cramped space compared with the same engine that I have in my Bavaria 37 where the engine looks lost in the vast (relatively) space available. The compartment never seems hot, even in the Med after long periods of running. There is no forced ventilation or fan, just a vent on the transom.

Remember when we were looking at new boats that Beneteaus and Jeanneaus had very cramped engine installations where you had to take half the boat apart to get at things, so perhaps that is why they have permanently running extractor fans.

 

[West Coast]

What you are saying is very relevant to this discussion. Looked at an engine installation on a Starlight like yours and was amazed at how the 2030 was shoehorned into such a cramped space compared with the same engine that I have in my Bavaria 37 where the engine looks lost in the vast (relatively) space available. The compartment never seems hot, even in the Med after long periods of running. There is no forced ventilation or fan, just a vent on the transom.

Remember when we were looking at new boats that Beneteaus and Jeanneaus had very cramped engine installations where you had to take half the boat apart to get at things, so perhaps that is why they have permanently running extractor fans.

The space is tight, but access is superb as the engine box top and sides can be quickly dismantled to get full access round the engine. Best I have ever had.

 

[Robert Wilson]

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.

I went for a sail yesterday and had to motor back to the mooring (bit like RTIR yesterday, poor guys).
I turned on my engine bay extractor while running engine at well over half throttle. The gale of wind exiting the cockpit vent was very impressive. I'm beginning to contemplate exiting the vent out of the transom to utilise the thrust in calm conditions!!
My extractor fan is of unknown origin, manufacture and age - but it works a heck of lot better than some posts on here suggest.

 

[30boat]

I went for a sail yesterday and had to motor back to the mooring (bit like RTIR yesterday, poor guys).
I turned on my engine bay extractor while running engine at well over half throttle. The gale of wind exiting the cockpit vent was very impressive. I'm beginning to contemplate exiting the vent out of the transom to utilise the thrust in calm conditions!!
My extractor fan is of unknown origin, manufacture and age - but it works a heck of lot better than some posts on here suggest.

Mine is a cheap Taiwan Jabsco knock of but has been in place for 14 years and is very powerful.Noisy too.

 

[Tranona]

The space is tight, but access is superb as the engine box top and sides can be quickly dismantled to get full access round the engine. Best I have ever had.

Yes, but I could see how engine compartment temperatures might be high with it all in place!

 

[Robert Wilson]

Mine is a cheap Taiwan Jabsco knock of but has been in place for 14 years and is very powerful.Noisy too.

Mine too, would spoil a quiet day's sail. But as using it means the engine is on I can up with it put (quote W.S. Churchill)

 

[neil1967]

My 2008 Jeanneau 36i (fitted with a Yanmar diesel) has an engine extractor fan that runs permanently when the engine is running, exiting out to the sugar scoop transom. Fitted as standard, I can't believe that Jeanneau would fit (or pay for) anything that wasn't needed - they want to keep the price as keen as possible. It can only be to extract hot air - the engine compartment is pretty small.

Neil

 

[dazautomatics]

I always love the amount of twits that post rubbish on her for the sake of arguing, when they blatantly haven't got clue what they are talking about! If the OP would like the opinion from another boat owner that has this set up then like others here we have a bilge blower which is thermostaticly controlled and run through the ignition (to save the battery's) And yes these do work as ours broke while motoring quite fast in the Carib which caused the motor to run very hot!
Maybe back in the UK they are not so much of a big necessity but controlled by a thermostat to improve fuel economy would be a good idea. And as for comments relating to the motor sucking more air, why is it when sailing in colder climes we can use our outlet as a hand warmer!!!!!!!
Hope this helps, happy venting!
Darren

 

[Tidewaiter2]

The OP has a small Southerly, ours is a S115, 1993 vintage and it too has a manually switched engine space extractor fan. The space is quite roomy compared to a lot of other yachts, i've been on and open to the aft bilge V.
I suspect it's there to vent before starting, but more importantly, to whisk post motoring/bilge smells away-and perhaps reduce the heat in the aft cabin-but as the first owner was a Clyde based Scot, I think it didn't get much use!
There is definitely a heat build up in the boat after an hour or so motoring, but thats useful in the UK Autumn, Winter,Spring and a chunk of the N European Summer.
Be interesting to know how many other Southerlies had it fitted-with a view to the Med, Caribbean Dream perhaps?

 

[Birdseye]

Any recomendations or a suitable fan to install for a 35 bhp engine?