Running Engine Blowers

If one blower is blowing in and the other blowing out, you're getting air in addition to that used for combustion circulating into and out of the engine room. If both blowers are blowing out of the engine room, you're sucking that much more cool outside air in from the engine room hull vents for both combustion and the air that's being exhausted out of the engine room, then the blowers are exhausting hot air from the engine room out. If no blowers are utilized then the engines are only sucking the amount of air into the engine room that they're using for combustion.

Please re read you own post at No 18, you have clearly stated that those engines can run with no blowers . I was curious as to how the engine room was cooled in that instance and now you tell me how the blowers work.

When I'm thinking of an issue that involves the design and set up of the boat, my first question would go to the builder. How did they engineer it and anticipate it working. Then I would test their design theories to see if they worked as intended.

Another question. Why aren't all engine rooms air conditioned? I don't mean down to 70 degrees, but some air. Could often just be the vents beyond the last vents. No thermostat, just air off the rest of the system.

Yes, most engines can run without the blowers on at cruise speed with no ill effects on the engines.

It also depends on the boat itself. If the hull vents are large enough and designed properly to keep salt out, you can run the blowers when the engines are running and it will help keep the engine room a few degrees cooler, while not necessary it does help with heat load inside the vessel as many engine room ceilings on motoryachts happen to have the salon on the other side of the floor and the foward engine room bulkhead happens to also have the interior of the vessel on the other side of the bulkhead. It also helps the air conditioners work more efficiently as many compressors are mounted in the engine room, so any lower temperature helps a little here and a little there.

On some to many yachts, the engine room vents will draw in a lot more salt with the blowers running due to air vent placement,size and design. On these yachts, if you run the blowers at cruise it puts a lot more salt into and onto the machinery and machinery space.

So it really depends on the yacht and who designed it and whether to run the blowers or not. But if you can run them at cruise rpm and keep the engine room salt free I would as it will usually help keep the engine room cooler provided the engine room vents are large enough to support both the air the engines and gen are used for combustion as well as what the blowers are exhausting.

K1W1, things are a lot different on the smaller yachts in regard to engine room design, air venting, and temperature of the engine room underway. Many of the smaller yachts 90'< have their air vents in the hull sides anywhere from 3-6' above the waterline. So if it's rough your getting spray and waves hitting the air intakes and such.....Megayachts have the luxury of pulling their engine room air intake from 20-40' above the waterline, far away from saltwater and spray usually.

I wasn't suggesting based on helping the engines although it might in some minor way, but really for the human element. Just surprises me how few engine rooms have air.

The amount of energy, cost and space required to make a major difference is what I am sure deters most.

There are some boats that do however cool the air coming into the machinery spaces buy having heat exchanger ( looks like a radiator core) mounted in the Air inlet trunking which is fed by sea water.

Not all engines have Charge Air Coolers and some if not all have a maximum inlet air temp , the non cooling of the machinery spaces and toughing it out promoted above does not seem to consider that there are other items in the machinery spaces other than the main engines that do benefit from being kept at a sensible temperature.

Electricity, the amount of BTU's needed and the amount of shorepower needed or generator power to run them is considerable and the gains don't justify the means.

So I guess I'll try to sum it up:

• Engines pull a massive amount of air through the engine room.
  
• Aftercooled engines don't care what the ambient air temperature is. People care about ambient air temp, but it can't be controlled when running the boat because of the volume of air vs. heat of engines.
  
• AirCond can help bring the temp down, once back at the dock.
  
• ER blowers are usually to exhaust hot air once the engines are shut down, but some manufacturers will use them to add air to the ER while running.

I'm not a surveyor, but I'll guess that ducting air from the salon to the engine room would not be good from a fumes, fire, and noise perspective. Air intakes in general are a source of onboard noise emanating from the engine room.

Aftercooled engines still care what the ambient air temperature is, it's just not as critical. However, the cooler the air, the denser it is, and the more power you will make. An engine is nothing more than an air pump and can only pump so many CFM's of air. 3 degrees change in the engine room is probably not noticable, 10 degrees would be. The aftercoolers can only take some much temperature out of the air charge. But the lower the engine room temperature, the better it is overall for everything.

I'll add a side note regarding air conditioning in an engine room. I recently added a 24,000btu unit to my engine room since I like to tinker and do much of my own maintenance and this time of year its a sweaty proposition. Engine rooms are designed to ventilate. It may seem obvious, but you will need to devise a way to close the engine room vents to keep the cool air in while at the dock for extended amounts of time. Otherwise, your attempts to cool the area will be futile.

A side advantage is the air conditioning keeps the bilges bone dry, humidity low, and salt air off the machinery.

I had always run the blowers while underway. I'm not sure why exactly. After reading this thread I will just run them after running for cooldown only.

Everything in your engine room will suffer prolonged exposure to elevated temps, you should do your best to keep the temp as low as you can.

I always run my blowers underway and after stopping.

MV Dirona, a Nordhavn 52, wrote recently about this topic.

The high points are that you can keep the engine room temp at an acceptable level even in 24/7 operation but it is work and takes time until you get it right.

It's like a commercial kitchen.......You ventilate it ,not air condition it. It would take a extremely large amount of AC to cool all the heat rejected by the engines. I would consider pumping AC into the engine room when the engines are off. This would only benefit if you do your own maintenance or your engineer/contractor would love you when he does it.

Actually some commercial kitchens are heavily air conditioned. The most difficult area I air conditioned in business was a commercial laundry and pressing area. We did use very powerful exhaust fans but we also used about three times normal air conditioning tonnage and had very large ducts about every ten feet throughout blowing directly on the operators. We were able to actually get it too cold. It's amazing what you can cool with enough exhaust power pulling the hot air out and enough air conditioning.