"Terry Spragg" wrote in message
.cable.rogers.com...

Use the blower for safety before starting your explosion machine.
After it starts, it will suck air much faster than any vent fan can.

A 454 cubic inch engine running at 3000 RPM and wide open throttle would
consume 394 cubic feet of air per minute. That is roughly what a standard
4" bilge blower will move.

Turn it off. Do not pressurize the engine compartment, especially
if you have a leaky exhaust.

Leaky exhausts are bad no matter what. Most bilge blowers draw air out of
the compartment, not force air in.

A flame arrestor
metal filter grille on an engine room exhaust vent driven by engine
vacuum seems a good idea, needing only a vent into the engine
combustion intake.

What?

You use a flame arrester to prevent a flame front in one area (generally a
small enclosed space) from spreading outside to a larger area. Like the
carburetor intake to the engine room. Where are you exhausting this engine
room to that you are trying to protect? Plan on driving this boat through
an explosive atmosphere?

A sufficiently strong "Intake air leak" will
evacuate any but the most catastophic exhaust leak into the engine
compartment.

I have no idea what you are trying to say here. Considering that the volume
of exhaust gases is an order of magnitude greater than the amount of intake
I don't see how you can make such a claim.

Engine air intakes are noisy, and require a dust
filter

Never seen a dust filter on a boat.

, so go a little further and build an intake muffler filter
box.

The air intake noise is nothing compared to the basic machinery noise of
the engine. If noise is a problem, silence the entire engine room!

Place any such vent as high as possible in the engine
compartment, in case of flooding. Provide a watertigh closure for
submerged running, if you are fitting a schnorkel.

Dust filters? Submerged running? Are we talking about boats here, or off
road vehicles? I have equipped vehicles so that they could wade across
rivers and keep running, but it isn't easy. It is not nearly as hard if you
have a diesel. On a gas engine you will have ignition problems long before
you have water ingested by the carburetor. If you are talking about
prolonged operation the starter and alternator will need a lot of attention
as well.


Use the leakage of air into the engine compartment as a cabin heat
circulation function, for instance, by placing the hot water
radiator in the bow. Fresh ventilation air could be drawn through a
heat exchanger incorperated into the engine compartment ventilation
/ combustion air intake filter, to improve efficiency in the heating

If you desire cabin heat, you will be much better off installing a heat
exchanger with a circulation fan and recirculating the cabin air through the
heat exchanger instead of constantly drawing fresh (cold) air into the
cabin.

It is generally unwise to have any air passages between the cabin and the
engine compartment.

The heat exchanger might accept cold water for air
conditioning, which could be cooled by a keel radiator pipe. When
it's 130 (F) out, sea water temperature air will be blessedly cool
by comparison, and won't eat up much power.

I have never been any place that was 130 (F). Where do you boat that gets
that hot? Most of the places that I do freqent where it gets what I
consider to be "hot" the water temperature, at least on the surface, gets to
be 75 to 80 degrees.


Some will say you should try to be safer with a tight engine box.
Don't ever depend on a tight engine box alone for protection from
fumes and fire.

You certainly want to have isolation between the engine compartment and the
cabin, but I have never heard of making the engine compartment itself air
tight. Such a design certainly wouldn't be legal in the USA.

Rod