Engine room heat and ventilation

[Redhook98]

Not sure where the original air inlets were for my 1979 49ft MT RPH. They are now located under the walkway steps and dump down into the ER with small vents. There are no built in blowers or ventilation in my ER.



Went for an 8 hour shakedown cruise last weekend. Engine room was quite hot when I returned. I estimate maybe 120 degrees. Both engines (FL120)s and gen going entire time. Did these older MTs originally come with forced ER ventilation? Just bought a Jabsco HD 4-inch flange mount blower to exhaust the ER. Sufficient?

 

[rslifkin]

If you're trying to remove heat, have the 4 inch blower draw from up high. As long as you have enough intake air to feed the blower plus the engines, you should be fine. It'll definitely help cool things down some, but until you try it, you won't know if it's enough or if it'll take more airflow.

 

[Redhook98]

Thanks, that is what my thought was as well. I do not think I have much air draw from my current motors, only running at 1700rpm or so. The air intakes now most likely are not factory spec'd, but then those may have been designed poorly as well. Every bit of decking, bulkheads, joists, supports, etc were replaced. I doubt the PO put it back to factory. More concerned about the heat.

If you're trying to remove heat, have the 4 inch blower draw from up high. As long as you have enough intake air to feed the blower plus the engines, you should be fine. It'll definitely help cool things down some, but until you try it, you won't know if it's enough or if it'll take more airflow.

 

[Lepke]

A 4" bilge blower probably won't change the temp by 10°. I think a lot less. And it would probably be better to blow air in. You don't want to create a negative air pressure in the ER. It makes the engines less fuel efficient.
Ships and tugs use big blowers in and out. No change in pressure and you move a lot of air. Some just use in blowers and let the engines take the air out. A positive pressure increases fuel efficiency.

 

[Comodave]

A 4” high mounted blower blowing out may help cool the ER down after running the boat but won’t do much if anything for cooling it down while running. Just not enough air movement. Check out Delta blowers if you really want to cool it down while running but hang on when you check the prices.

 

[Redhook98]

I was afraid of this. Once again, all good advice. It is a big ER. Made even bigger by reducing tankage from 1000 gallons to 300. Lots and lots of empty space to circulate. I may add another exhaust and port to my lazerette. Or one for in and one for out.

 

[oscar]

My Detroits produce a LOT of heat.... Yes 110ºF in the engine room is normal. And they stay warm to the touch for a LONG time..... like 24 hours. I have a 4" fan in each engine room. I don't bother. They are noisy and I don't see any difference. Luckily Hatteras went through great lengths to sound and heat insulate the engine rooms. So as long as the thick doors are closed I'm OK. And if it gets a little chilly I open them and WHOOSH.... temperature in the whole boat goes up several degrees in minutes.

 

[slowgoesit]

120 degrees! Wow, on a recent 9 hour run with our new to us boat, OAT (Outside air temp) was around 70 degrees, engine, a Gardner 8LXB, in a large engine room running at normal cruise of around 1400 RPM, the air temperature gauge in the engine room showed a steady 85 degrees. We have both an intake ER fan, and an exhaust ER fan, but neither was on. Two Dorade box vents are always open. Personally, I think 120 degrees is a problem. Good luck with addressing your heat issues!

 

[Portage_Bay]

I think you're going to need more than a 4" fan. And as Lepke points out in post #4 blow the air in. You said the original build ventilation has been reduced by a PO.



Think of your engines as air pumps. They move a LOT of air.


Here's the arithmetic, those better at engines than I may correct the 2nd step.

1. FL 120 is 380 cu in displacement
2. There are 3 detonations per revolution, so 190 cu in air moved per rev
3. 190 * 1700 RPM = 32,300 cu in moved per min
4. 64,600 cu in moved for twins
5. 373.8 cu ft moved for twins

Open up more ventilation. If you need more air push it in. With a bigger blower.

 

[Martin J]

There has been previous threads on this subject. I did post a cat manual in the library on this subject. In my previous boat I upgraded my ventilation and reduced the er temp by 20defees F. The engines adored me after that (FL 120's) We were in the eastern Caribbean for 7 years cruising. The cooler the engine room the less wear on the rest of the equipment as well. On my current boat I have upgraded to 1000cuft coming in and 500cuft going out.

The cooler air you can get to your er and the engine intakes the bigger bang in the cylinder! Engines run better and more power on cold damp air than hot engine room air. Hence they become more economical.

It is my intention to improve on this with some better gas flowed ducting rather than rely on the wooden square trunking that was installed when built. This is a case of doing some cabinet work in the saloon to achieve this. There's a great store in MI I think that I get my fans from , they are only $60-70. I switch mine on the bridge though a 30/40 amp relay. https://www.amazon.com/gp/product/B017VDI0GY/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

 

[Martin J]

Try downloading this Caterpillar engine room ventilation guide.

https://www.trawlerforum.com/forums/downloads.php?do=file&id=108

 

[rslifkin]

On the powered air intake thing, I don't like it. I much prefer powered exhaust only, and either an equal or less amount of powered intake, or just natural draft intakes big enough to not put the ER under vacuum with the exhaust fans on and the engines at high power.

Pressurizing the ER with intake air risks forcing heat and smells into other parts of the boat where you don't want them.

 

[Martin J]

rslifkin Smells vs power and efficiency? I know which I would choose. I would spend the time to seal my engine room properly. If you think about it 1000 cuft in 500 cuft out with engines that if i remember consume approx 500cuft per min cruising. It sort of balances.

Its nice to walk in to a engine room underway without having to lose 10lbs of sweat and 130-140 F of heat.

It's not that ahrd to seal a engine room there are spray foams/ sealants that do the job admirable,

 

[oscar]

Now you all have me thinking. I have massive openings into the engine room. Plenty coming IN. But the exhausts fans are 4" and lethargic at best. Any ideas for a high CFM fan? Right now they are 32V but 110 is available......

 

[rslifkin]

rslifkin Smells vs power and efficiency? I know which I would choose. I would spend the time to seal my engine room properly. If you think about it 1000 cuft in 500 cuft out with engines that if i remember consume approx 500cuft per min cruising. It sort of balances.

Its nice to walk in to a engine room underway without having to lose 10lbs of sweat and 130-140 F of heat.

It's not that ahrd to seal a engine room there are spray foams/ sealants that do the job admirable,

Yes, it can be done, although it's easier on some boats than others (mine has shaft holes through the aft bulkhead as the shaft logs are outside the engine room, for example). But in general, as long as your intakes are big enough, natural draft intake will keep up just fine without pulling a measurable vacuum in the ER.



I've actually thought about hooking up a sensitive vacuum gauge to see what the air pressure in my ER is while running, as I only have 4x 5" intake ducts, plus whatever air gets pulled through the shaft holes, etc. Although if I'm working the engines hard, I rarely have the blowers on as the engines are already moving a lot of air (and my blowers pull from down low so they don't do much for heat anyway).

 

[twistedtree]

On the powered air intake thing, I don't like it. I much prefer powered exhaust only, and either an equal or less amount of powered intake, or just natural draft intakes big enough to not put the ER under vacuum with the exhaust fans on and the engines at high power.

Pressurizing the ER with intake air risks forcing heat and smells into other parts of the boat where you don't want them.

Agreed. A slight negative pressure in the ER is ideal. Not so much that it causes the engine to gasp, but just enough so air flow through all the gaps and voids in the boat runs into the engine room, not from the engine room into the living space.

 

[Pete Meisinger]

I guess I don't understand what is wrong with a warm engine room. Most marine diesels run too cool anyway. 120 degrees does not sound hot to me.

I have an indoor/outdoor thermometer mounted on the flybridge, where I do most of my driving. The indoor temp is the ambient air temp, sometimes nice to know. The outdoor temp is from a sensor in the engine room. (wireless) If the temp suddenly rockets, I know I have a problem. I don't figure I need one on the lower helm station. I'm close enough that I would smell trouble or feel it on my feet.

pete

 

[twistedtree]

Now you all have me thinking. I have massive openings into the engine room. Plenty coming IN. But the exhausts fans are 4" and lethargic at best. Any ideas for a high CFM fan? Right now they are 32V but 110 is available......

Are the output ducts/vents similarly large? The size of the vents/ducts really matters. I have seem them badly undersized to the point where a larger fan actually makes maters worse, not better.

 

[Bacchus]

The cooler air you can get to your er and the engine intakes the bigger bang in the cylinder! Engines run better and more power on cold damp air than hot engine room air. Hence they become more economical.

I'm trying to understand this but missing something...
I get the cool part as cool air denser and you get more inspiration so helps combustion of fuel.
Why does moisture help?
Humid air less dense than dry air and would seem to be a detriment vs dry?

 

[twistedtree]

I guess I don't understand what is wrong with a warm engine room. Most marine diesels run too cool anyway. 120 degrees does not sound hot to me.

I have an indoor/outdoor thermometer mounted on the flybridge, where I do most of my driving. The indoor temp is the ambient air temp, sometimes nice to know. The outdoor temp is from a sensor in the engine room. (wireless) If the temp suddenly rockets, I know I have a problem. I don't figure I need one on the lower helm station. I'm close enough that I would smell trouble or feel it on my feet.

pete

The core engine probably doesn't care much, but it's generally all the other stuff. The most common specs I have seen from equipment manufacturers (engines and generators) is 130F max temp, and 30F max temp rise over ambient. You need to be below both numbers.


Things that suffer are engine seals, alternators, and any electrical equipment like battery chargers, inverters, generators, batteries themselves, vent fans, pumps, etc. And of course you, if you need to be in the ER. Speaking of vent fans, I have seen plenty with temp ratings around 110F, and they don't last long at 130F.

 

[FF]

Pushing air into an engine room can be a problem.

Most boat ER are not boats are easy to seal, every penetration , hose , wire , pipe whatever must be sealed air tight.

The danger is an exhaust leak might be quiet , but have enough volume to kill , or reduce mental ability if exhaust or fire is pushed into the cabin area.

Delta T Systems makes large capacity blowers to evacuate engine rooms.

These need to be wired to shut down if fighting a fire, before CO2 or Halon is used.

 

[Martin J]

Hot air = thin light
Hot humid = slightly heavier
Cold air +heavier Better
Cold damp air heavier Much better
The tendency is for a engine in thin air say to replace lack of air to replace it with fuel to reach the same hp.

The heavier the air the better. Think about how your car operates at 12000ft going over a mountain pass. It struggles in the thin air. whereas the ratio of oxygen is the same in air. There is approx 20% -40% less oxygen in a breath at that height.
https://www.higherpeak.com/altitudechart.html

 

[DCDC]

Stella has a big integrated locker (~8x3x4) under the pilot house windows with Dorade intakes ducted to 9” Delta T blowers forward of the engines, Deere 6068’s. An 8” blower aft of the engines pulls air out. Additional louver vents are on the cabin sides and the dry stack housings. Blowers are interlocked to shutdown if the Fireboy extinguisher system triggers.

We have a Bluetooth temperature transmitter in the ER and highest temperature so far is 106F cruising Florida/Bahamas/Gulf Coast including several 24+ hour runs.

Photos are Dorade intakes, Delta T fan, exhaust blower and ER discharge vent.

 

[dannc]

Profession Boat Building magazine has at least a couple of articles in issues 109 and 110, written by Gerr, about ventilation.

https://pbbackissues.advanced-pub.com/?issueID=109&pageID=130

https://pbbackissues.advanced-pub.com/?issueID=110&pageID=106

The part II of the article, the second link above, is about ventilation in ER and machinery spaces and includes the calculations need to figure out how much air flow is needed.

Later,
Dan

 

[GoneDiving]

Also consider the air path when the blower is on. Cold air should be added to the bottom of the space and exhaust from the top of the furthest wall. This will exchange the air in the whole space and prevent pooling of any hot or noxious fumes. If the inlet and outlet are close together the air will just jump between the two and not actually pump out the hot, stale air. The same for the external inlet and exhaust points. They should not be too close it you will just pump the same air round and round.

Duct sizes should facilitate flow. There is no point having a large blower trying to suck or blow through a small restriction. Painted grates/screens over the inlet dramatically restrict airflow.

Blower sizing should allow for the room volume to be changed ~20 times and hour.

 

[FlyWright]

I have 1977 twin Perkins 4.236 85's in an ER without fans...just fore and aft fixed SS louvers on each side. My temperature 'delta' typically runs 30*F to occasionally 35*F between ambient and ER temps. I bought a cheap dual temp sensing AcuRite Digital In/Out temp displays that I use to monitor the spread.

We typically have 100*+ days on the CA Delta and I've never seen anything over 130*F...but lots over 120. TBH, if it was my boat, I wouldn't worry about it but I'd watch the spread.