Engine Room Blowers being replaced, Setup for In on Port and Out on Starboard?

[The Brockerts]

Replacing the blowers in my engine room that are 34 years old and not working. Engine room is 2 3208's and generator ,4 feet high.

Right now the 3 blowers are all setup to pull air out, 2 on starbroard and 1 on port. I thinking of setting it up different. Set up 2 on Port side bringing fresh air in and set up 2 on the Starboard to pull air out.

I'm I over thinking this? What is really needed?

 

[Mac2]

I have twin 3208s as well. Got smoldering without fans. I added two 110v blowers to the starboard vent. Port vent is identical and both vents are centered on engine. These fans have a high/low setting and I added a thermostat. Results: way to much air flow! It made my hair blow in the wind, and Im bald. Added an off switch to one fan. I’ve only used one fan in mild temps, but the low setting was enough to maintain cool temps in the engine room, which is approximately 7x 12 x 20. The port side has no fan.

 

[BB-marine]

I believe passive air for suction and mechanical for exhaust. The important part of engine compartment ventilation is have enough passive ventilation for the engines to pull air for proper combustion and exhaust blowers to remove warm air and maintain a slight negative pressure in the engine compartment when the engines are running.
Brian

 

[Mac2]

I believe passive air for suction and mechanical for exhaust. The important part of engine compartment ventilation is have enough passive ventilation for the engines to pull air for proper combustion and exhaust blowers to remove warm air and maintain a slight negative pressure in the engine compartment when the engines are running.
Brian

If you have an airtight engine room with two vents, I don't think it's possible to exhaust more air (with fan) than what can come in the passive vent, correct?

 

[Diep]

I'm not necessarily an expert but I would go with BB and use fans only for exhaust. Then make sure you have enough free area of vent for intake so that you don't starve the fans or the engine. If you send air out mechanically (fans and engine exhaust) it will have no problem coming in if you provide a way.

I would use an intake fan only if you are trying to duct fresh/cool air to a specific area. On my boat this is done with a small fan ducted to an air-cooled refer unit in the ER. I've seen people try to direct cool air to their alternators.

No matter what I think you want more fan power on exhaust than intake. You want to avoid having positive pressure in the ER and pushing air into the cabins in pretty much all circumstances.

 

[Delta Riverat]

I have 4 engine room vents and 2 exhaust blowers on the aft vents. The forward vents are not powered. The forward vents are just in front of the engines and the aft are right above the transmissions.

In operation I don't turn the blowers on, the air intake from the engines cools the ER. I use the blowers after I turn the engines off.

This seems to work well, highest recorded ER temp was 110F in 85F outdoor.

 

[BB-marine]

If you have an airtight engine room with two vents, I don't think it's possible to exhaust more air (with fan) than what can come in the passive vent, correct?

I believe if you were exhausting more air from the fans and engine than can come through the passive vents a negative pressure in the compartment would be the results.
Brian

 

[hmason]

My boat was built with one fan blowing in and one fan blowing out.

 

[klee wyck]

The two 3208 will move almost 1000 cfm just for intake/exhaust air so you should already have a good passive intake vent somewhere. I doubt exhaust fans will do much while the engines are running in most boats but could be helpful after the engines shut off if you need to be in there for something or need to keep an inverter cool.
The engines are likely doing 50 complete air exchanges per hour for the engine room while running.

 

[Mac2]

The two 3208 will move almost 1000 cfm just for intake/exhaust air so you should already have a good passive intake vent somewhere. I doubt exhaust fans will do much while the engines are running in most boats but could be helpful after the engines shut off if you need to be in there for something or need to keep an inverter cool.
The engines are likely doing 50 complete air exchanges per hour for the engine room while running.

I had two passive vents. My engine room would get well above 100 degrees. The two blowers I added pushed up to 800 cfm each. I ended up using one blower on low for 550 cfm. This kept my engine room at approximately 70 degrees F. I believe this works so well due to how airtight my engine room is. The air being pushed out forces air to be sucked in the other vent. If I crack the engine room door, I loose all air movement across the engines.

 

[boomerang]

Ideally , when the engines are running, you'd have a slight positive pressure in the engine room so the engines have combustion air without having to "labor" at all. The same thing blowers, superchargers and turbos are designed to accomplish. In addition, positive pressure keeps salt air and dirt from being sucked into the engine room. Unfortunately, thats all but impossible on a recreational boat with a couple of 12v exhaust blowers and the engine room intakes on the side of the hull. Ships and larger boats use several blowers that get their clean air from higher up and force it down into the engine room through strategically placed discharge vents, where it keeps a positive ER pressure for the engines ,plus it scavenges the hot air through strategically placed discharge vents. Again, darn near impossible on a typical yacht so I'd just use the 12v blowers to exhaust the hot air (or combustible fumes if it's a gas/petrol boat) from the ER when the engines aren't running.

 

[psneeld]

This is what I have heard pretty much my whole life. I have used the slight negative pressure as my engine(s) are rarely working hard and the boats were small enough without airtight engine rooms that would cause the whole boat to smell like an engine room if positive pressurized.

Exhaust Fans
Ventilation air exhaust systems should be designed to maintain a slight positive or negative pressure in the engine room, depending on the specific application.
Positive pressure should normally not exceed .050 kPa or (0.2 in. H2O).
This positive pressure provides the following advantages.
• It prevents the ingress of dust and dirt, which is especially beneficial for those applications involving engines that draw their combustion air from the engine room.
• It creates an out draft to expel heat and odor from the engine room.
Some applications, such as a marine application where the engine room is adjacent to living quarters,
require that a slight negative pressure be maintained in the engine room. This negative pressure should not normally exceed 0.1275 kPa (0.5 in. H2O). The excess exhaust ventilation provides the following advantages.
• It compensates for the thermal expansion of incoming air.
• It creates an in draft to confine heat and odor to the engine room.

Calculation of Engine Room Ventilation

GENERAL The primary aspects of a properly designed engine room ventilation system are cooling air and combustion air. Cooling air refers to the flow of air that removes radiant heat from the engine, generator, other driven equipment and other engine room components.

www.linkedin.com

 

[rslifkin]

I agree with avoiding positive pressure to avoid pushing smells, etc. into the boat. A bigger challenge with a not-perfectly-sealed engine room is smells after shutdown though (unless you leave the blowers running for a couple of hours while the engines cool).

 

[Blissboat]

Every inspected vessel I have worked aboard with diesel engines has had its E.R. blower on the exhaust side only. As that fan pulls air out of the compartment, fresh outside air flows in (from an intake on the opposite side of the E.R.) to replace the air in the compartment naturally. When all engines are running at speed, the fresh air enters at a greater velocity, enough so as to maintain equilibrium. That's why the intake opening is larger than the exhaust side - it allows the incoming airflow to find its own happy spot.

 

[dannc]

The OP might want to read these links,
- Engine Room Ventilation – Editorial: Carcasses and Wishy-Washy Quote-Filled Articles | Steve D'Antonio Marine Consulting
- Adventures of Tanglewood
- Professional Boat Building magazine #109 and #110 by Gerr provide quite a bit of information and equations. These editions should be available for download on the Professional Boat Builder website.
- See https://deltatsystems.com/ for Delta T products.

 

[O C Diver]

When I redid the exhaust fan on my boat, I did some research. First, I chose to only use an exhaust fan. Secondly, I added additional fresh air in areas to support the requirements for the engine, generator, and exhaust fan. In addition, I directed the air flow to come in through the bilge in the forward part of the engine room. Finally, the exhaust fan was mounted next to the ceiling in the stern of the engine room.

The ideal is to bring in fresh air at the lowest point. Heat rises to the ceiling. Remove the hottest air from the ceiling. Ideally have the fresh air in and exhaust out from opposite ends. The thermometer probe at the ceiling usually was below 110 degrees after an 8 hour cruise day.

My one 4" exhaust fan near the ceiling, top center:

Ted

 

[Diep]

Excellent links dannc. Thanks for the informative additions.

 

[dannc]

Excellent links dannc. Thanks for the informative additions.

You are welcome.

 

[twistedtree]

Excellent links dannc. Thanks for the informative additions.

Here's a link right to the ER cooling article on www.MVTanglewood.com

Engine Room Cooling

Nordhavn N60 cruising. Grand Banks cruising. Nordhavn 68. Marine electronics.

www.mvtanglewood.com

 

[Halinbrier]

Has anyone set up their engine room blowers on a thermostat so they will turn on automatically when the engine room gets hot during passage?

 

[Mac2]

Yes. See above pics

 

[SIBERNUT]

My personal feeling is that i dont want *anything* feeding air into a space with fuel and potential spark not under my control. An otherwise controllable fire could trigger it.

 

[Halinbrier]

Yes. See above pics

Thanks Mac. I didn't realize that was a thermostat. It looks like your fans are 110v? I have Jabsco 12v fans and am having trouble finding a thermostat and relay for a 12v set up.

 

[Mac2]

Thanks Mac. I didn't realize that was a thermostat. It looks like your fans are 110v? I have Jabsco 12v fans and am having trouble finding a thermostat and relay for a 12v set up.

Yes. 110 volt. That will be hard to find a 12 volt thermostat.

 

[3rdOrderEffect]

Yes. 110 volt. That will be hard to find a 12 volt thermostat.

The OP should search for a 12V PID temperature controller. Plenty of them on Amazon that can control any device and are fully programmable to include hysteresis.


Here is an example

https://www.amazon.com/Powered-Universal-Temperature-Controller-Thermocouple/dp/B01EK73OVA/ref=mp_s_a_1_9?crid=3S63SKD0F4FKS&dib=eyJ2IjoiMSJ9.Y0hJ1eZsnoUQ7MwtMaV28FofIVhmL83r-JIZW58lkHq76njpBkt67RLpTaR8EloJY3VH3lAqV4stXLwex9kPMOhvkc6etFWCSbn4fjiGSa6BvVmuB5Be7zUkUjiylgwutNttmJLubNi6yaxeCUx3NLLl4UXsO1dIkJ8u_XGFKzMNGceYzwrnEudOFTLgcS6newzExwTFdRHN0j8gP4Un9w.HIWB3lx_jOct77S0aQAalS-5EzL2IkRYmNE_VFcg6QA&dib_tag=se&keywords=12v+pid+temperature+controller&qid=1745017494&sprefix=12V+pid%2Caps%2C128&sr=8-9

 

[twistedtree]

Or something like this https://www.amazon.com/Adjustable-M...45054266&sprefix=din+themostat,aps,133&sr=8-5

 

[Bacchus]

First and most important for safety...
If you are modifying ER venting... (either blowing in or out) and have an ER fire suppression system, I believe it is best practice / ABYC reqmt to wire fans through the fire suppression system control module. This stops forced air flow in case of system being triggered. If that's not done the fire suppression system will be much less effective as it is sized for ER volume w/o infiltration.

Second... re the argument that forced air is cleaner, less salty than natural ventilation caused by negative pressure... that would only be true if you ducted the intake from a location that is "cleaner" such as from fly bridge level where salt spray may not be as plentiful.
If you are simply using the natural vent opening and adding a fan you will get the same / similar quality air so the argument fails logic. My MS ER intake openning includes a "mist Eli jinator" designed fins that, in principle, should minimize salt air mist from entering. I would guess that some other mfgrs may include a similar arrangement.

 

[sealandsky]

Also agreeing that all blowers should be exhausting the air. Sharing a nice trick that my fav marina tech came up with on my boat - It seems that none of the blowers out there are all that quiet or well-balanced so they cause noise and vibration that can be felt around the boat. He used short pieces of 1 1/4" rubber hose as vibration dampeners by attaching the hose to the bulkhead, then mounting the blower to the hose with machine screws and washers. Now they are quiet and vibration free!

 

[Bacchus]

Also agreeing that all blowers should be exhausting the air. Sharing a nice trick that my fav marina tech came up with on my boat - It seems that none of the blowers out there are all that quiet or well-balanced so they cause noise and vibration that can be felt around the boat. He used short pieces of 1 1/4" rubber hose as vibration dampeners by attaching the hose to the bulkhead, then mounting the blower to the hose with machine screws and washers. Now they are quiet and vibration free!

Same mounting works great for fresh water pumps

 

[BB-marine]

Sucking warm air out using mechanical devises ) exhaust blowers is the way to go. Passive in, mechanical out when needed. I purchased a Cutwater in 2016 new. It had nice sized vents on both sides of the pilot house trunk. At least I thought it did! We used the boat on Lake Michigan for the first 3 months of owning it. The Lake water temperature was at most 70F and the ambient air temperature was always cooler on the lake than on shore. Engine compartment temperature seemed warm but not alarming. We took a trip From Lake Michigan (Racine Wisconsin ) to the Tennessee river. (Illinois, Mississippi, Ohio, Tennessee rivers in August. The river water temperatures in the 80's and ambient air temperatures matched that mid 80's. I noticed that the engine compartment was very warm! Actually I started smelling my waste tank that was in the engine compartment. I used my infrared temp gun to check tank temperature and it was 140F. It was warm in the compartment. I checked to see if the vent hoses were obstructed and found there were none. The vents on the pilot house trunk were fake. There was no compartment ventilation.

I contacted Fluid Motion industries ( Cutwater-Ranger Tug). I asked " where is the engine compartment ventilation ?" The answer was " it's a diesel the ABYC does not require ventilation in the recommendations for diesel power plant vessels"???

I then installed three air temperature sensors in the engine compartment. I found that at cruising speed of 2250 rpm or higher the compartment temperature would be as high has 165F ( ABYC recommendation is no higher than 122F). I then reached out to Fluid Motion Industries and told them the compartment temperatures. " Don't worry about that, it is fine" !!!

I worried about it and contacted the NMMA.The Cutwater is NMMA certified vessel. I gave them documentation of my findings. They responded that this does not meet the recommendations. There was nothing they could do or recommend. Really!!

I designed a ventilation system in the boat. I did make a PVC manifold and utilized one of the fake vents and installed 4 other vents and opened up areas between the cockpit sole and the hull to help get air into the compartment. I installed (1) 250 CFM 12V and a 150CFM blower that were operated by switches. I installed a wireless temp sender in the compartment and a temp gauge at the dash. When I saw compartment temperatures above 120F I would manually turn the blowers on. I did not want thermostatic controlled blowers. I preferred to monitor and manage. It was a small boat easy to do.

Before installing the ventilation I read many articles that stated a slight negative pressure should be present in the compartment. The engine and exhaust mechanical blowers should be used to suck warm air out and fresh cool air in . The engine intake and exhaust blowers should be located high in the compartment and intake passive vents should have hoses that are placed in lower areas of the compartment. (Diesel engines only) Gas powered this is done differently.

Below are photos of the install I did in a Cutwater. After the install was completed I monitored compartment temperatures. Before install temperatures maintained 160F to 170F after 115F to 125F. When I saw the compartment temperature going above 120F I would turn the blowers on. I left them on until I saw the compartment temp below 120F.

Passive intake and Mechanical exhaust with temperature monitoring was my approach.
Brian