Re: [OMC-Boats] timing/carb adjustment

Nice explanation, Ethan. Also another compromise of marine vents is that
while they do offer an exhuast port for air, that same opening can allow
unwanted water into the vessel.

Lee
----- Original Message -----
From: "Ethan Brodsky" <brodskye@...>
To: "Evinrude & Johnson Boats of the 1960's and 70's"
<omc-boats@...>
Sent: Wednesday, July 30, 2008 9:19 AM
Subject: Re: [OMC-Boats] timing/carb adjustment

> On Wed, 30 Jul 2008, JEFF DOOD wrote:
>> the design of all these I/O boats out there still boggles my mind -
>> all these components have to be marine to prevent sparks because off
>> all the gas fumes that can accumulate under the tightly sealed
>> cowlings. And why are they tightly sealed? to prevent noise!?
>> um......why put noise considerations over VENTILATION OF THE ENGINE
>> COMPARTMENT BOMB! it just doesn't make sense. i guess some boats
>> have the vents needed to draw out the air. but if they all did such
>> a good job at venting, there wouldn't be all these requirements for
>> marine components to prevent spark. we could all just use car
>> parts. they should vent the cowlings like crazy and figure some
>> other way to control the noise. imo. i'm done venting now - haha.
>
> The difference between cars and boats is that boats need to float. :P If a
> fuel line breaks in your car or your carb float bowl valve sticks (hehe)
> or you have any other sort of fuel-releasing malfunction, the fuel just
> pours out the bottom of the car and makes a puddle on the ground. In a
> boat, the fuel pools in the bilge.
>
>
> The engine compartment is necessarily a poorly ventilated space. It's
> basically a "pit" - it will generally always have a lower point where
> fumes
> can accumulate. Even with the cover entirely off, it's still likely that
> gas vapor concentrations over the lower explosive limit could develop if a
> gallon or so of fuel was spilled in the bilge and you were sitting still
> (with no wind to force air through it). Any source of ignition would then
> lead to an explosion (which would ignite the rest of the puddle), so it's
> necessary to actively vent the compartment before doing anything that
> might
> lead to a spark.
>
> That's why it's absolutely necessary to run the blower prior to starting
> the engine, to continue running it during low-speed operation when there
> isn't enough wind to naturally vent the compartment, and to make sure that
> the inlets for the compartment exhaust pull from the bottom, where
> explosive vapors are likely to concentrate. Extra vents won't make much
> of
> a difference, because the risk is mostly at start-up, when there's no wind
> to help naturally vent the space.
>
> Ethan
>
> --
> Ethan Brodsky
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Received on Wednesday, 30 July 2008