Engine Ventilation: Skip it?

[forsailbyowner]

I wasn't cited. I had a bower motor connected. If he would have stuck his hand next to it hed have found out it wasn't blowing any air. A rat had ate his way through the blower cage to get into the boat. Have since installed new blower and a grate over the cowlings to stop the pesky rodents.

[Stevens 47]

I take it then, that if one is limited to only 1 exterior (outside the boat) engine room vent source (pipe), that vent should be used as a blower exhaust or blowing air out through it. The engine air intake would have to take care of itself via compartment vents built into the engine compartment, drawing air from inside the boat. Jack

[atoll]

coming up the red sea,a few years back,in a brand new 67 ft yacht,found that we werent getting very good fuel economy when motor sailing to windward,plus the engine room was getting very hot ,ambient temp outside about 35.c.
turns out the 2 blowers were both rigged to suck air out.
cut a long story short rigged both to blow air in,engine room much cooler,fuel consumption went from 15/lph to 12/lph............
only other thing i would do is to have a third less noisey fan extracting hot air ,after shut down of engine and blowers.

[Eleven]

More on Engine Oil Management for the Long Term Cruiser. This comes from an engineering site discussing a system that involved slowly adding fresh oil and taking the excess sump oil to the engine diesel feed and burning it through the engine. NOT recommended. The alternate scheme was:
The best thing you can do for an engines life is use a system like the amsoil bypass filtration system. There are a few other systems like it, as well. It also takes oil from the sump, but runs it through a very effective oil filter, basically a roll of paper towels. The wood fibers in the towels increase in strength with oil, so they wont fall apart. the oil then goes back into the engine. I think the army is now doing 100,000 mile oil changes, or somthing crazy like that, because the extra filtration keeps the oil like new. Diesel will still work its way in to some oil systems, so inexpensive used oil analysis should be done a few times before relying on 100,000 between changes. Also, fuel from the local pump is usually only filtered to about 20 micron. Filtering your fuel down to 5 micron, or even less, will greatly increase engine life.

I still stand by my comments on Oil Temperature where the engine is enclosed and is not a 'works' installation. Oil Temp is a the best indicator of a good installation.

[barnakiel]

Well, sort of depends:

If your engine room is NOT very well sound-proofed NEITHER very air tight, AND if you sail in cold / mild climes AND if you have a small engine, then perhaps.

But in any other case my recommendation would be to have the blower, or two.

Never forget the diesel engine is called the diesel engine but it does need air to run too.

And if you happen to have a big alternator with a temp sensor you will see how often it switches off, if you do not keep the engine room cool.

b.

[mbrault]

Your motor is an organ. It needs fresh air. That is the primary reason why manifacturers want you to vent your engine room. I bet the main reason for your fan to go bad is because it was trying to push air out, working against your mega air pump; your engine.

here are some calculations based on a very common yanmar 4JH5E engine (55HP):
Engine displacement: 134 CI (Cubic inch)
Engine speed: 3000 RPM
CFM: 116.31

This motor need 116 CFM (Cubic feet per minute) to be happy. Probably the volume equivalent to the size of a small office (12 x 12) in less then 10 minutes.

The performence of your engine is proportional to the density of the air coming in (temperature). The heavier, the better. Light air (hot) doesn't have enough oxygen in a given volume (the size of your piston) to make your motor happy. Although it will run, it is not efficient.

SOLUTION:

• Get the intake from outside using the proper devices / conduit. You can buy a plastic car bowl (the SAAB model is just perfect) with a filter which will reduce any noise, filter dust and separate water (very important). This is a very small investment and will assure you of the best preformence (more importantly, better combustion leading to a longer motor life and much better for the environment)
• Blow the air outside of the engine room. This will avoid any odors from getting into the boat. This blower wont blow out this time!

.....

"The idea behind a cold air intake is simple... Since cooler air is denser, the theory is that you will be able to pump the cylinders with more air with each stroke. The cooler the incoming air temperature, the denser the intake charge. The resulting cold air intake temperature creates more power & improves fuel economy." Diesel Performance Guide | Diesel Performance Database

[David M]

Originally Posted by GordMay

OOPS, I got caught in Davids's editing.

On GASOLINE POWERED Vessels.

The United States Coast Guard's mandatory requirements for ventilation for boats with gasoline engines for propulsion or auxiliary machinery are found in 33 CFR, Subpart K, Sections CFR 183.601 - 183.630. Refer to the CFR for complete, current federal requirements.

Additionally, see ABYC H-2, Ventilation of Boats Using Gasoline.

In addition to Natural Ventilation (required), these standards require Powered Ventilation (at least 1 Blower per Gas Engine).

***

ABYC Standard H-32
Ventilation Of Boats Using Diesel Fuel states:
"power or natural ventilation is not required on a diesel boat, but may be used to control compartment temperature." The standard also provides guidance on other ventilation considerations such as supplying necessary combustion air, venting hydrogen gas from batteries when appropriate, and removing the discharge from fixed gaseous fire extinguishing systems.

ABYC’s "Ventilation Compliance Guideline" (#COMP005, 64 pages, ± $120) guides you through the calculations for net compartment volume and ventilation system design. Covers powered and natural ventilation, as well as ventilation of fuel tank compartments and determining blower system output.

On passenger for hire vessels powered ventilation is required in engine spaces, diesel or gas. Although not required of a diesel recreational vessel as Gord notes, it might be a good idea anyway if the CFR's thinks it's a good idea.