Engine room ventilation

[O C Diver]

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.

It's common to find engine room ventilation on modern larger boats and small ships, especially when crew frequent the engine room while underway. The objective is to make the engine room a more hospitable place as more and more electronic components (such as engine computers, electronic regulators for alternators, and electronic controls for generators) are now in engine rooms. Also consider that many boats operate in tropical waters where otherwise, engine room temperatures could easily exceed engine and generator manufacturer's limits.

Putting my hand over the blower discharge while the engine is at cruise RPM with the transmission in neutral, clearly demonstrates the blower is still exhausting a substantial amount of air.

Ted

 

[garbler]

I’ve never worked on a ship, tug or ferry that did not have engine ventilator fans and on most larger tugs and large commercial fish there is a fidley above machinery which allows lots of intake air into the space (S). Now here is the rub with forced or fan ventilators. The USCG, Lloyds, ABS and all others require automatic ventilator shut downs and shutters or doors when fire alarms go off. This should give you guys a heads up on what blowers can do to in fire situations. (1) they remove any all fire suppression agent from the space if they are exhaust type, and (2) if intake blowers can and will excite a fire to beyond your capability quite quickly. Exhaust blowers will do the same but maybe lesser degree depending on make-up air. . So having your blowers linked to your fire alarms isn’t a bad idea. But you still have blower openings and they provide extra air for a fire. Normally this kind of equipment is found primarily on larger vessels but from what I see here there are quite a few bigger vessels that reach the bar

Rick

 

[twistedtree]

Ventilation basically serves three purposes.


1) Extraction of explosive fumes prior to starting the engine. This is only applicable to gasoline/petrol engines.


2) Provide makeup combustion air to run the engine. This can vary widely depending on the engine size and power output. Sometimes passive intakes are fine, and sometimes mechanical assist (fans) are needed. Every engine has specs for how much combustion air it requires, and passive intake vent size requirements. I expect many builder do not provide for this adequately. I know I have seen a few.


3) Provide cooling for the engine compartment/room. Every engine also has specs for it's operating environment, usually in terms of absolute temp around the engine, temp rise over outside air temp, intake air temp at the manifold, etc. Also, other equipment in an engine space like inverters, electronic controls, batteries, may have more restrictive temp requirements. This is mostly more stuff for builders to ignore or guess about. Sometimes the air exchange for combustion air is enough to keep the compartment/room cool enough. In other cases some form or forced ventilation is required to move through additional air to keep temps under control.


If anyone is interested, Cat has a good paper on engine ventilation. It's primarily geared towards generators in buildings, but all the principals apply to boat engine rooms as well.

 

[garbler]

Ventilation basically serves three purposes.


1) Extraction of explosive fumes prior to starting the engine. This is only applicable to gasoline/petrol engines.


2) Provide makeup combustion air to run the engine. This can vary widely depending on the engine size and power output. Sometimes passive intakes are fine, and sometimes mechanical assist (fans) are needed. Every engine has specs for how much combustion air it requires, and passive intake vent size requirements. I expect many builder do not provide for this adequately. I know I have seen a few.


3) Provide cooling for the engine compartment/room. Every engine also has specs for it's operating environment, usually in terms of absolute temp around the engine, temp rise over outside air temp, intake air temp at the manifold, etc. Also, other equipment in an engine space like inverters, electronic controls, batteries, may have more restrictive temp requirements. This is mostly more stuff for builders to ignore or guess about. Sometimes the air exchange for combustion air is enough to keep the compartment/room cool enough. In other cases some form or forced ventilation is required to move through additional air to keep temps under control.


If anyone is interested, Cat has a good paper on engine ventilation. It's primarily geared towards generators in buildings, but all the principals apply to boat engine rooms as well.

Good stuff thanks
Rick

 

[Steve DAntonio]

This is really a function of the temperature of the air being ingested by the engine vs. outside air temp, referred to as "Delta T". Since you didn't provide those measurements it's difficult to render an opinion.

Some engine rooms do OK with passive ventilation, others not so much. If you want to know which category yours falls into, take some measurements, using a digital thermometer at the air intake, adjacent to the filter, and another thermometer outside, in the shade, run the vessel at a range of rpm, but primarily at your cruising speed, for a minimum of 4 hours, 8 is better, to "heat soak" the engine room, then evaluate your readings. I'm not sure if Perkins provides a max allowable DT, but in its absence 25 deg. F is what's typically used as the maximum allowable.

Keep in mind, engine room temp affects everything in the ER, electronics, hoses, insulation, belts, rubber mounts etc., not just the engine.

Details here https://www.proboat.com/2015/06/venting-the-engineroom/

 

[catalinajack]

This is really a function of the temperature of the air being ingested by the engine vs. outside air temp, referred to as "Delta T". Since you didn't provide those measurements it's difficult to render an opinion.



Some engine rooms do OK with passive ventilation, others not so much. If you want to know which category yours falls into, take some measurements, using a digital thermometer at the air intake, adjacent to the filter, and another thermometer outside, in the shade, run the vessel at a range of rpm, but primarily at your cruising speed, for a minimum of 4 hours, 8 is better, to "heat soak" the engine room, then evaluate your readings. I'm not sure if Perkins provides a max allowable DT, but in its absence 25 deg. F is what's typically used as the maximum allowable.



Keep in mind, engine room temp affects everything in the ER, electronics, hoses, insulation, belts, rubber mounts etc., not just the engine.



Details here https://www.proboat.com/2015/06/venting-the-engineroom/

Good rule of thumb to know, that 25 degrees. I have often wondered whether I should be using the exhaust blower that lives in my engine room (twin Lehman 120s). I have not. The boat is a DeFever 44. The engine room access is a somewhat large 2' x 4' door near the v-berth. The v-berth has a ventilation hatch close to the engine room door. We run with the door and hatch open and the aft door door open also. With the movement of the boat this creates a natural draft that pulls heat out of the engine room. While it is indeed warmer in the engine room, the Delta T is nowhere near 25 degrees although I have never measured the difference. Every boat has a story.

 

[Marco Flamingo]

Ventilation basically serves three purposes.


1) Extraction of explosive fumes prior to starting the engine. This is only applicable to gasoline/petrol engines.

And boats that have propane onboard. And boats that have aerosol cans onboard (paint, deodorant, cooking oil, etc. commonly have heavier than air propellants like nitrous oxide, propane, n-butane and isobutane). And boats that have lead acid batteries onboard. I've gotten rid of all but the batteries, so I still blow the bilge before starting my diesel engine.

 

[Cold Duck]

Have had 5 diesel boats 30-70ft. All were designed with passive airflow. Never had an issue with any of them. Doesn't mean some boats were designed poorly, but the MS has plenty of airflow. Time to find another project.

 

[hollywood8118]

And boats that have propane onboard. And boats that have aerosol cans onboard (paint, deodorant, cooking oil, etc. commonly have heavier than air propellants like nitrous oxide, propane, n-butane and isobutane). And boats that have lead acid batteries onboard. I've gotten rid of all but the batteries, so I still blow the bilge before starting my diesel engine.

Has ANYONE ever heard of a DIESEL boat blowing up from anything other than a PROPANE leak?


My boat has a bunch of aerosol cans and I don't worry a bit, propane BBQ cylinders I keep in the propane locker with the big tanks as I HAVE seen one of those leak.
Hollywood

 

[Cold Duck]

A little off subject, but while cruising, all the boat fires were involving cooking fuels. Propane gets a bad rap. All of the fires were from handling the cooking fuels, alcohol, kerosene, etc. The more you handle an open fuel the better chance of an accident. Once the propane is connected, tested and vented in an appropriate location, it is far safer than the other fuels. Never saw a propane fire while cruising. Used a propane refer for 2 years. We were the only ones with a reliable refer but this was back in the 70s so there are now more efficient cooling systems. Electric cooking is better, but smaller vessels have issues with the power. I think you would have a better risk of fire from the blower burning out and starting a fire than the diesel fumes in the bilge.

 

[Marco Flamingo]

Has ANYONE ever heard of a DIESEL boat blowing up from anything other than a PROPANE leak?


My boat has a bunch of aerosol cans and I don't worry a bit, propane BBQ cylinders I keep in the propane locker with the big tanks as I HAVE seen one of those leak.
Hollywood

When a boat with propane blows up, propane would get the blame even if the cause was an old can of Right Guard that fell over and discharged. The incident I heard about was an aerosol can that didn't fall over, it simply rusted out. I can't think of any aerosol product that is immediately needed onboard or isn't available in a non-aerosol version. So I also don't worry a bit.

 

[rgano]

Ted nailed the implications of trying to ventilate an ER. My 1972 Grand Banks came to me in 1986 with what looked and felt like a factory installed 12-volt exhaust fan. After not properly evaluating the situation, I started running the fan underway with two 120 Ford-Lehmans gulping air. The fan soon burned out. It took me a bit to figure out that this was a moored-only fan to suck some of the routinely 120F heat out of the ER after a day of running. Maybe if I had installed another intake fan, I could have successfully run the exhaust too, but the possibility of pressurizing the ER and pushing all its odors and heat into the boat held me back - besides the air inlets were not all that big in the first place, and I did not want to obstruct them, there being no place to cut another vent hole. I like the Vents brushless 120-Volt exhaust fan I have attached to my Nextgen generator's electrical end - it seem like it will far, far outlast the crappy Jabsco 12-Volt fan that came with the boat.

 

[BruceK]

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.

I get the idea of lowering ER temp after closing down engines but, check the substantial ammeter draw of those fans. Seems somehow wrong to anchor, and immediately put a 20A+ load on the batts. Not to say you shouldn`t, but..
The Integrity with twin 210 Cummins ER seems to get warmer than the IG with twin 120 Lehmans. Cunningly, the outlet fan on the IG sat immediately above the eutectic fridge/freezer compressor unit.

 

[Delta Riverat]

I know, 12 amps each. One is going out (loud bearings) and I bought a brushless replacement that only pulls 9. I'm going to test it for a year (cheap Chinese unit but really moves air) and if it proves itself I'll get another and use the other good (not load) Jabsco as a spare

 

[Steve DAntonio]

Ted nailed the implications of trying to ventilate an ER. My 1972 Grand Banks came to me in 1986 with what looked and felt like a factory installed 12-volt exhaust fan. After not properly evaluating the situation, I started running the fan underway with two 120 Ford-Lehmans gulping air. The fan soon burned out. It took me a bit to figure out that this was a moored-only fan to suck some of the routinely 120F heat out of the ER after a day of running. Maybe if I had installed another intake fan, I could have successfully run the exhaust too, but the possibility of pressurizing the ER and pushing all its odors and heat into the boat held me back - besides the air inlets were not all that big in the first place, and I did not want to obstruct them, there being no place to cut another vent hole. I like the Vents brushless 120-Volt exhaust fan I have attached to my Nextgen generator's electrical end - it seem like it will far, far outlast the crappy Jabsco 12-Volt fan that came with the boat.

Indeed, some fans are continuous duty, others are not. The classic "squirrel cage" blowers are continuous, the in-line "tubular" fans usually are not. Make sure you know which you have before running continuously.

 

[ronobrien]

If you install a fan to bring air in you run the risk of pressurizing the ER and forcing hot air into the cabin. If you install a fan to pull out you run the risk of creating a negative atmosphere and starving the engine of air. These are both pretty unlikely scenarios, just pointing out theories. I worked on a 112 Westport that had forced intake to the ER or the engines would starve for air.

 

[timb7734]

I owned a trawler for ten years, that I had built that had twin Yanmar 4 cylinder engines and no engine room ventilation. Over 2500 hours I had no problems other than repositioning the Victron inverter to the utility room to lower the heat. Never any corrosion in the engine room, always in salt. Still going strong with a different owner in the Great Lakes.

 

[Mambo42]

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.

I wrote about it about a year ago. Temps in my engine room were up to 130 - 140 degrees F, it was like a sauna. As it turned out the ventilation in the engine room was well below what was necessary.
I did find a changed hatch for the lazarette, which was basically a honey comb structure, so the former owner did know about it as well.
After some research and talks with boat builders I understood the max temp should be around 100, but preferably around 85 F.
So I bought 2 industrial ventilators. One with a hose taking hot air out of the engine room and one blowing fresh air in. Each ventilator has a capacity of 4500 m3 per hour. As a result I keep the temp at about 80 degrees in the engine room while underway. On cooler days I can get away with just one blower, the openings in the ER (4 in total) draw in enough cool air to just pump the hot air out.
The ventilators draw a total 600 W at 220 V or 25 A at 24 V and I have that available when the engines are running.

One of the side effects of the hot temperatures in the ER before was that a lot of electricity cables are just hardened completely and had become brittle. In some cases the insulation just fell apart. So that problem is immediately fixed as well