Engine room blowers

[tadhana]

Back in the early 1990s several boat companies, including Hatteras, Bertram and Sea Ray looked into this in some detail. This might not apply to our trawlers but on a boat such as Hatteras running at speed the engine draws in so much air that even if the blowers were trying to pull air out, the engines will run the blower fan blades backwards. While to boat is running, the engine is a huge air pump and keeps cool air flowing into the engine space. The problems arise after shutdown when the engine goes into heat soak. Engine room temperatures easily rise to 140 and temperatures as high as 170 have been seen. This is when and why you need engine room blowers on a diesel.

 

[psneeld]

Do keep in mind scale.

My neighbors 54 Betram has twin Detroits and burns 55 gal per hr at cruise.

My boat burns 2 gph or less.

My engineroom is way bigger in terms of airspace surrounding the engine and my air intakes arent that much smaller.

I have pretty good sized blowers for my needs...not sure what he has but I bet mine are way more effective because of the scale difference.

 

[twistedtree]

Here's a blog article on ER cooling in a trawler


Adventures of Tanglewood: Engine Room Cooling


In this case, the engine consumes about 1000 CFM of air, but a total of about 3000 CFM is needed to keep the ER at a temp rise of 20-25F. The extra 2000 CFM requires exhaust fans. That's continuous airflow while underway, not just when you shut down. Without it, the temp just climbs and climbs and climbs. If you are doing short runs it won't be a big issue, but if you run for 4-6hrs or more, let alone 24x7, it's a problem. It's hard on equipment, and downright dangerous if you need to spend any time in the ER fixing something.


As for intake vs exhaust, both will get the air out. Intake fans will pressurize the ER and push the air out through vents or other passages. Exhaust fans will create a vacuum and pull air in through vents and other passages. The ideal situation is with a bit more exhaust than intake such that there is a slight negative pressure (vacuum) in the ER. That prevents smells and heat from being pushed out into the boat through various unplanned paths.


In a boat with sufficient ducts and vents, there is no need for both intake and exhaust fans. Air coming in has to equal air going out. And with a desire for ER negative pressure, that means exhaust fans are preferred, and intake fans, if of matched flow capacity, will have no effect and are not needed. The only situation where intake fans will help is where there are intake duct restrictions that need to be overcome.


One other thing to not overlook is fan shutdown if you have an automatic fire extinguishing system in the ER. For those to do their job, they need to be paired with an engine shutdown system that kills the engines and fans if the fire system triggers. Otherwise, if the fans and engines are allowed to keep running even briefly, they will evacuate all the fire suppressant before it can do it's job.

 

[dieck]

Our boat has four blowers in the engine room. The two forward ones blow air in, and the two aft ones suck air out.

To me it would seem more efficient to have all of them sucking air out and just let the air find its own way in. But what do I know.

I rarely use them since they make a horrendous amount of noise.

Is there a good reason to leave them in their current configuration, or should I change them so all four exhaust air from the engine room?

When an engine runs, it sucks in so much fresh air that no further ventilation of the ER is needed. On a diesel the blowers are only needed to cool the engines and the ER after shut down. Since all ER have a light smell that you dont want in the cabins you want a lower pressure in the engine room which means that the blowers should suck out. Also extreme Ventilation does not accelerate the cooling process. Try to define how much Ventilation you Need and install the right blowers. I run mine for over two hours depending on outside temperature and they are silent.

 

[twistedtree]

When an engine runs, it sucks in so much fresh air that no further ventilation of the ER is needed. On a diesel the blowers are only needed to cool the engines and the ER after shut down. Since all ER have a light smell that you dont want in the cabins you want a lower pressure in the engine room which means that the blowers should suck out. Also extreme Ventilation does not accelerate the cooling process. Try to define how much Ventilation you Need and install the right blowers. I run mine for over two hours depending on outside temperature and they are silent.

This may be true at some scale/size, but there are configurations where power ventilation is absolutely needed. Our boat is an example. Twice again the air flow of the engine is needed to maintain temp.


Caterpillar has a good guide/booklet on cooling engine rooms. It's primarily targeted at generators in buildings, but the principals are all the same, and the same formulas apply.

 

[Wil]

Interesting thread. Having only one intake blower that is really loud, need to upgrade the Deere 4045TFM/Northern Lights 8KW ER ventilation system. Also unfortunately both the house and machinery battery banks are in there as well.

Does anyone have a recommendation for quiet but powerful 12v (or 24v) blowers?

 

[twistedtree]

Interesting thread. Having only one intake blower that is really loud, need to upgrade the Deere 4045TFM/Northern Lights 8KW ER ventilation system. Also unfortunately both the house and machinery battery banks are in there as well.

Does anyone have a recommendation for quiet but powerful 12v (or 24v) blowers?

Delta-T makes a number of different fans in 12 and 24VDC. Fantech has a number too.

 

[Aquabelle]

I can strongly recommend these reasonably priced ventilation fans from Vetus, available in both 12 v & 24v models: https://www.vetus.com/en/search/?q=fan+178

They have much higher air capacity than the usual "squirrel " type blowers and they are not noisy. I have a pair I installed in 2009 and I run them continuously while underway and for some time after shutdown...still going strong.

 

[Martin J]

Nice to see this subject come up again, many people do not realize the cool engine room benefits. It's not just the less wear and tear on rubber products, but the better engine performance of the engine ingesting cooler ,denser air giving more bang for your buck. But the quieter running engine and the abilty to spend time in there without being reduced to a dripping mess. In my last boat I fitted 2 x 550cuft extractions fans pulling from the exhaust vicinities and 2 blowers blowing cooler ambient air at the air intake areas of the engine. The result dropped 30F in the engine room and the engines ran at the desired temps, ran smoother on the denser sir and better fuel consumption.

You should read this from Caterpillar http://s7d2.scene7.com/is/content/Caterpillar/CM20160713-53120-44971
Also you can get 550cuft fans from The surplus center https://www.surpluscenter.com/Elect...C-Rotom-R7-522-Centrifugal-Blower-16-1541.axd $60
Then there's always Steve D'Antonio's article https://www.proboat.com/2015/06/venting-the-engineroom/

 

[fryedaze]

Several have suggested that they run fans for 1/2 to 1hr after shutdown. I run the fans as long as I can. When at anchor after a 5-8hr run in warmer conditions the ER retains heat a long time. The two 500 lb blocks and 2000 lbs of fuel provide a lot of heat storage that takes a long time to cool.
While working the boat this week I discovered that the subfloor in the salon is a sandwich of two 3/4" teak plwood with 2" of foam between. Probably helps with sound and heat.

 

[Wil]

Thank you for the recommendations.

This might be the article TT was speaking of:
https://www.cat.com/en_US/articles/...-generator-rooms-for-optimum-performance.html

 

[BIG CAT]

Food for thought. For 1 degree rise in inlet air temp. Exhaust temp will rise 3.