thejonesey
Active member
Hello all,
Do you run engine bay fans when going along or only on start up? TAMD61a on shaft in a Turbo 36.
Do you run engine bay fans when going along or only on start up? TAMD61a on shaft in a Turbo 36.
Numpty Question Engine Fans
- Thread starter thejonesey
- Start date
Parabolica
Active member
I leave mine on whilst running. Can only be a good thing imv
jon and michie
Well-known member
Ditto
Momac
Well-known member
The purpose of fans is presumably to maintain a slight negative pressure in the engine bay and help to avoid any fumes entering the accommodation space (on a mid engined boat) and the fans would also reduce fumes in the engine bay in case the engine bay needs to be accessed while the engines are hot.
Therefore it would seem sensible for the fans to operate while the engines are running and for the fans to keep running several minutes after the engines ave stopped.
I expect there are other opinions on the purpose of the fans.
Therefore it would seem sensible for the fans to operate while the engines are running and for the fans to keep running several minutes after the engines ave stopped.
I expect there are other opinions on the purpose of the fans.
SC35
Well-known member
They probably also keep the engine bay a little cooler on a hot day.
I don’t have a choice - mine fire up at the same as the engines.
I don’t have a choice - mine fire up at the same as the engines.
piratos
Member
In earlier days I used fans when starting Gasolin engines, but with my Tamd61 I never used the fans.
There are differnet set ups - and on some ships/boats fans are used to suck additional air into the engine room.
LBRodders
Well-known member
The TAMD61a is 306hp extraction fan, and its safe to say that in a Turbo 36 there is 2.
No engine bay fan is going to have an effect on the volume of air they both draw, particularly at decent revs.
So my 2p is that the vent fans are fitted for use prior to engine bay access and post long running when the engines may be red hot and will benefit [as will the boat] on engine bay cooling.
No engine bay fan is going to have an effect on the volume of air they both draw, particularly at decent revs.
So my 2p is that the vent fans are fitted for use prior to engine bay access and post long running when the engines may be red hot and will benefit [as will the boat] on engine bay cooling.
Portofino
Well-known member
Why ? ……it’s pointless with a diesel as they are glorified air pumps anyhow .
Any poxy fans 9issing in the wind ( no pun intended )
Engine displacement 12L x 1800rpm x 60 mins 1296000 L x 2 ( twin ) = 2592000 L / hr @ atmospheric pressure it’s drawn it .
Any poxy fans 9issing in the wind ( no pun intended )
Engine displacement 12L x 1800rpm x 60 mins 1296000 L x 2 ( twin ) = 2592000 L / hr @ atmospheric pressure it’s drawn it .
Chris H
Active member
Your engine room must get unbearably hot……I’ve installed an extra huge fan to move air around……engines don’t like hot air !
Scubadoo
Well-known member
I thought the main purpose (well perhaps for older boats) was to vent the engine bay in case of fumes mainly for Petrol engines but also battery gases etc. I do out of habit run the fan for a couple of minutes before starting.
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Portofino
Well-known member
No cos all that air flowing in through the side vents , some 2.5 million litres / hr vol at atmospheric.
Aside the intercoolers sea water cooled bring it down anyhow iirc to approx 15 *c from my MMDS screen I can see the charge air temps ( after the cooler ) ,It’s more a Q of how efficient the intercoolers are , how beefy and up to to job .
No matter what entry temp air is when it’s “ turbo d it’s compressed and heated ….up anyhow to same temp .
Its all on the intercooler efficiency after the turbo at the end of the day which is function of seawater temp and pump pressure .In the winter it works better gets it down from 15 to 11 due to the colder seawater flowing .
With normally aspirated sure I see your point .But not with turbo seawater cooled intercoolers .
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Portofino
Well-known member
Yes it’s a bit historical , pre diesel turbo intercooler ( Water cooled ) .
The other thing not touched upon thus far is fire ! You don’t want too many air holes in / out of the ER .Wether main vents or additional fan entrances/ exits .
On my boat built for charter it’s not got fans .The side air vents are spring triggered to shut air tight with internal flaps .
Should there be a fire I can close all the air entrances with toggles on the helm .As well as close the diesel cocks on the tanks and manually remotely trigger the gas bottle if its wax bulbs not done this already .Separate emergency engine cut outs too .
The phase “ fanning the flames” springs to mind .Panicking getting all muddled up cos ER fires aren’t everyday .
The only benefit of fans in a turbo diesel intercooler set up is as said helping to prevent heat soak at shut down .Particularly if you need to dive in to the ER for quick maintenance.Not sure how marina neighbours will approve of the racket ?
Btw your fuel tanks basically act as huge oil storage radiators and the bigger the iron block that too heat soaked once the water cooling ceases at the dock .
thejonesey
Active member
Thanks everyone for your thoughts. I always vent before but it seems like there is differing opinion on running. I hadn’t thought about the idea of venting to cool down.
Chris H
Active member
Not sure you’re getting this……….if the air temp in the engine room is lower the engine will receive cooler air, the inter cooler will only reduce temp from a set point to another set point, depending on how efficient the inter cooler is, ………..if air goes into the engine @ 40 deg the inter cooler may take it down to 30 deg, if the air is 30 deg the intercooler will take it to 20 deg…..engines like cold air.
If air enters the engine @ 60 or 50 or 40 deg the intercooler will not cool the output air to 20 deg, the numbers maybe out but the principal is the same.
Momac
Well-known member
That's principle, not principal.
I agree engines like cold air because cold air it is more dense than hot air. But with the engine running a little engine bay fan will make no difference to engine bay air temperature.
The engine itself is a much bigger consumer of air compared to a little fan. So the engine drawing in outside air obliterates the effect of the fan , especially so when the engine is running at speed.
ss2016
Member
I have a VP D6, no fans. I have a max/min thermometer in the engine room. I have never seen it read more than about 95F / 35C and it only gets there after a run. It must be considerably cooler when gulping fresh sea air in the Channel.
Chris H
Active member
You’ve not seen the size of my engine room fan !
On the few occasions I’ve had to go into the engine room when running, the heat was unbearable, from experience, after fitting a large fan, it has drastically reduced the engine room temp.
ohh……and principal or whatever is how spellcheck rights it
Momac
Well-known member
Both spellings are correct but different meaningohh……and principal or whatever is how spellcheck rights it
No I haven't seen the size of your fan.
Portofino
Well-known member
But you are missing the turbo compressing it and heating it to circa 200 *c or what ever .You might need to check the post turbo air temp . Your “ set point “ isn’t ambient ER temp it’s the post turbo temp .
The bigger the turbo set up the higher the temp , the bigger the intercoolers to cope etc .
Your MAN s are well endowed turbo and intercooler wise .
As I said you are correct with a normally aspirated engine .like your geny for example.
Portofino
Well-known member
@ Chris I’ve looked it up for you
What is the temperature of the air after a turbocharger?
During compression in the turbocharger or supercharger the air is heated (adiabatic process) to the range of 230-260 °F. This hot intake air then passes through the intercooler where heat, if the intercooler is properly designed, is removed.
Principle is the same my numbers in post 19 were estimated .
What is the temperature of the air after a turbocharger?
During compression in the turbocharger or supercharger the air is heated (adiabatic process) to the range of 230-260 °F. This hot intake air then passes through the intercooler where heat, if the intercooler is properly designed, is removed.
Principle is the same my numbers in post 19 were estimated .
