Engine room ventilation

[PhilPB]

I'm sure this has been discussed before but I couldn't find a definitive answer. Our older Mainship engine room with single Perkins turbo 165hp has passive ventilation out both port and starboard sides via rather good sized vents. Bought it a little over a year ago and have been updating and redoing quite a bit. Should I install any fans to either pull in or blow out? Have run the motor for hours and engine area doesn't get hot nor smell much. Not that I'm running out of projects but I was wondering if it is necessary.

 

[READY]

Given you are not seeing much heat rise I would find another project.

 

[mvweebles]

Given you are not seeing much heat rise I would find another project.

Well put. Only thing I can add to OP is if you ever do install a fan, make sure you buy one that is rated for continuous duty. The most common fans I've found are Jabsco. The less expensive one has a lower CFM, but mostly it's rated for intermittent use. There are reports of them giving out in a few months of regular use.

Peter

 

[PM]

Is it broken?

pete

 

[RT Firefly]

Greetings,
Mr. P. "Not that I'm running out of projects..." Patience. Something will pop up. Put those hardly necessary fans at the bottom of your list. IF you get really bored, re-post your question in 4 or 5 years...or read a good book.

 

[PhilPB]

It's not that I'm bored, just a little ambitious at times. So I take it CO is not an issue either? We do run the generator for a/c at anchor. Pete, I loved your answer!

 

[O C Diver]

I added an exhaust blower when doing my refit. My reasons were as follows:

Nothing good comes from an elevated engine room temperature.

If you cruise multiple days in a row and your fuel tanks are in the engine room, elevated fuel temperatures may reduce efficiency.

Electrical power generators (engine alternator and generator end) live much longer happier lives in lower ambient temperatures.

Most battery manufacturers recommend keeping the batteries as cool as possible when bulk charging.

On my boat the main inverter is mounted in the engine room. Keeping it as cool as reasonable improves life expectancy.

I run a 220 CFM blower through an optimized duct to get close to 200 CFM. The blower runs whenever the engine or generator are running. I consider the blower a consumable at $35 +/-. In my application they last routinely about 1,000 hours, one year of my cruising.

There are some important considerations when installing a exhaust blower. First, make sure you have enough fresh air intake (measured in square inches) to properly supply the engine(s), generator, and the BLOWER. You ideally want to exhaust heat as opposed to using the blower for air intake. Pressurizing the engine room may force heat and associated smells into living areas of the boat. If the engine or generator has an exhaust gas leak, you may also push those toxic gasses into other parts of the boat. If you have an engine room automatic fire suppression system, it needs to have a control box that shuts the engine and generator down to keep the suppression gas in the engine room. The ventilation blower would need to be controlled by this control box. Ideally, you want to mount the blower at the highest point in the engine room and want the fresh air to enter the engine room at the lowest point, as far away as practical.

Ted

 

[Delta Riverat]

My Island Gypsy has (2) 4 inch blowers exhausting close to rear of engines. Also 2 large intakes at the front of the engine room. The manual advises to run them to reduce engine room temperature. I checked and there is a good amount of warm air coming out after a day on the water, so I let them run for a good 20 minutes after I shut down.

 

[Bacchus]

Phil
My '08 34HT has a blower but I never run it while cruising. As others mentioned, it is helpful to run after shutting down to help remove some of that hot air from the ER.
CO should not be an issue assuming your are diesel for both main eng & gen.

 

[Comodave]

Yes, typically diesels do not make a significant amount of CO like gas engines do. But they do need lots of intake air so running a blower without having enough make up air could be an issue.

 

[RT Firefly]

Greetings,
Mr. P. Having read the subsequent posts to mine (#5), I withdraw that hasty, frivolous opinion.

Move blower calculations, blower selection and installation UP your list in consideration of added safety and longevity.

Remind me not to get into the xmas egg nog until AFTER 10:00AM.

 

[mvweebles]

Not sure I understand the CO comments. It's a byproduct of incomplete combustion common to all internal combustion engines (complete/perfect combustion results in CO2 + H2O). Regardless, this CO/CO2 should go out the exhaust, no residual in Engine Room unless there is something wrong, no?

Did I miss something?

Peter

 

[garbler]

I’ve sea trialed boats where the saloon sole was carpeted and while underway the hatches were lifted and the RPM’s increased. Starving for intake air and honestly not that uncommon

Rick

 

[Comodave]

Yes, if the engine room door/hatches slam shut while running it is a indicator of air starvation. Before you add exhaust fans and use them while running make sure you have adequate make up air coming into the engine room.

 

[Comodave]

Diesels tend to exhaust less CO than gassers. There is maybe still enough to kill you just not as likely. Here is one comment I found about it. I still have a CO monitor on our diesel boat but on multiple diesel boats they have never gone off. On previous gas boats the monitor would occasionally go off if the wind would blow the exhaust back aboard.

Because diesels are more efficient, they do in fact emit less carbon dioxide than gasoline engines. Diesel fuel contains about 12 percent more energy per gallon than ordinary gasoline, and about 16 percent more energy than gasoline that contains ethanol.

 

[Delta Riverat]

Diesels make very little CO as they always operate with more air than is required for complete combustion. Gasoline needs a slightly rich mixture to run smooth, thus the need for oxygen sensors and then a catalytic converter to deal with the unburned hydrocarbons.

 

[O C Diver]

Diesels make very little CO as they always operate with more air than is required for complete combustion. Gasoline needs a slightly rich mixture to run smooth, thus the need for oxygen sensors and then a catalytic converter to deal with the unburned hydrocarbons.

Yes, but diesels produce a lot of carbon dioxide which will also kill you, but just requires a larger exposure.

Ted

 

[Delta Riverat]

Yes, 10% for CO2

200 ppm (.02%) for CO

 

[Marco Flamingo]

I’ve wondered about ventilation in my engine room. The PO had cut some raggedy holes over the years and I’ve been closing them up for sound attenuation. But I haven’t really seen anything that looks like it was original ventilation, certainly nothing that mechanically exhausts outside of the engine room.

What I did do was install a simple battery-operated temperature/humidity alarm that Bluetooth’s to my phone. The only time I’ve had ER temperature approach 90 degrees is after shutting down on a long cruise. When traveling, ER temp is usually about 70 (on a common PNW 50 degree day). It seems my 80hp Lehman is injesting enough air to keep the ER reasonable.

I actually installed the Bluetooth gadget as much for the humidity notification. Sitting in the marina, I’ve had the humidity go above 80%. It always drops when cruising as the ER temp goes up. My thinking was that if I had a cooling system/exhaust leak while underway, it would drive humidity over 90% (the set point) and that would alert me to a problem even before notification of a temp problem.

Seems the consensus is if all is well there is no point adding ventilation. Okay by me.

 

[markpierce]

Suck the bad air out, let fresh air come by itself.

 

[Insequent]

I have pair of Delta T 9" axial fans near my intake vents.https://deltatsystems.com/wp-conten.../09/9-Inch-12-VDC-Fan-Spec-Sheet-2021-Web.pdf

Then just to rear of engines, which will exhaust a lot of air of course, I have a pair of 200 cfm in line blowers at ER ceiling directing air to the rear ER vents to remove hot air

 

[garbler]

Diesel engines don’t normally mind heat, they love it within reason. But they need oxygen and most Taiwanese trawlers I’ve seen lack sufficient hull and machinery space ventilation. Luckily those Lehmans aren’t real demanding they seem to do well in most engine rooms. If they react when you open doors and hatches then they probably need more air.

Rick

 

[catalinajack]

For all the folks running blowers, I would be interested to know what the before and after temps after running your fans vs not running fans for the same amount of time. I wonder whether the difference is worth the bother. Perhaps.

 

[heysteve]

When I think of hot engine rooms, I always think of Steve McQueen in Sand Pebbles

 

[RT Firefly]

Greetings,
Mr. h. Valve not wowve....Yep. Good flick.

 

[O C Diver]

For all the folks running blowers, I would be interested to know what the before and after temps after running your fans vs not running fans for the same amount of time. I wonder whether the difference is worth the bother. Perhaps.

That's actually a good question, but the answer is complicated. I see about a 10 to 15 degree differential in temperature when the blower is running.

However, my remote temperature sensor is about 6" below the ceiling. The exhaust blower is about 6" below the ceiling at the opposite end of the room. 70% of the intake air comes into the room down the hollow keel. Heat rises. So the ceiling is quite warm; the hull is cold; the air in between varies. The engine room air is exchanged twice per minute at normal cruise with the blower accounting for half of the exchange.

I've gone into the engine room and closed the hatch with the engine at cruise RPM and transmission in neutral after 8 hours of cruising. The air flow (400 CFM) and associated turbulence is surprising. The temperature varies quite a bit. The heat radiating off the engine feels like being near a camp fire. Most other things feel luke warm to very warm depending on how close to the engine they are. There seems to be a substantial improvement and the cost in electricity and blower replacement is negligible.

Ted

 

[SteveK]

I always thought a blower was to remove any possible combustible air prior to starting. Once the engines are running I doubt the blower is doing any air movement. Blowers are a carryover from gas engine boats, a safety feature not usually needed with diesel.

 

[Choices]

It would be a fairly easy calculation to figure air consumption; engine cubic inches x rpm x stroke factor (4 cycle is 1/2, 2 cycle is 1). I think.

Then roughly estimate cubic inches of the engine room.

This will give you how long it takes to turn the engine room air, and then calculate airflow through the vents.

On a big sports fisherman at speed hatches can be hard to open. On my little 36 with a single Lehman, not an issue at 1800 rpm.

Engine room temps should be close to ambient while motoring, only becoming elevated when the engine is killed with no blowers.

I run my blowers once docked for thirty minutes, then maybe one more time in a hour.

 

[Choices]

Those calcs are for naturally aspirated.

 

[rslifkin]

I always thought a blower was to remove any possible combustible air prior to starting. Once the engines are running I doubt the blower is doing any air movement. Blowers are a carryover from gas engine boats, a safety feature not usually needed with diesel.

That's their purpose on a gas boat, but if the blower system is appropriately designed for it they can be useful for heat removal.