Page 5 - WestlawnMasthead20_Dec11

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Adding a carbon canister to the vent line is an entirely new
component—a significant change aboard gasoline boats.
The expansion of the fuel in the tank during the day sends
vapor through the vent and thus through the carbon canister
and the carbon absorbs much of the hydrocarbons. When
the cycle is reversed during cooling at night, air passes back
into the vent and through the carbon canister. This purges
the carbon of most of the hydrocarbons returning them to
the tank.
Carbon canisters are nothing more than a sealed container
filled with activated charcoal. It usually most convenient to
fabricate them in roughly cylindrical shapes out of pipe or
tube, with inlet and exit barbs at each end.
Minimum canister size is calculated as follows :
For boats less than or equal to 26 feet, the canister size in
liters = 0.04 x Fuel tank capacity in gallons.
EXAMPLE: An 18-foot boat with a 25-gallon tank would re-
quire a canister of 0.04 x 25 = 1.0 liters
For boats greater than 26
feet the canister size in
Liters = 0.016 x Fuel tank
capacity in gallons.
EXAMPLE: A 30 foot boat
with a 250 gallon tank
would require a canister of
0.016 x 250 = 4.0 liters
If convenient for some
reason, two or more canis-
ters can be strung in series to meet the required minimum
volume. Perko and Attwood are two manufacturers produc-
ing carbon canisters.
The reason there are different requirements for boats less
than and greater than 26 feet is that the EPA determined
that boats larger than 26 feet would usually spend more
time in the water. The water moderates the cooling and
heating effect driving diurnal emissions, so—on average—
larger boats can be expected to have proportionally lower
diurnal emissions, which can be handled by smaller carbon
An enormous amount of testing was done by NMMA, simu-
lating the worst-case heating and cooling cycle. The results
enabled NMMA to negotiate a more realistic number than
was originally offered by the EPA.
Installing the required carbon canister creates some new
issues of its own. The carbon is very sensitive to liquid im-
mersion—water and fuel. Liquid has to be kept from entering
the canister. In fact—on many vessels—typical boaters de
mine when their tank has been topped off during fueling
watching to see when gasoline starts spilling out of the v
If this happens with a carbon canister in the vent line, the
canister will, obviously, be completely flooded with fuel.
Finally, the canister itself is an interesting component. D
it need to meet the 2-1/2 minute burn test? (Yes if inside
the engine compartment, no if outside.) How should it be
mounted? Can it handle boat shock and vibration? How
about prolonged low (or high) temp winter storage? How
we measure its effectiveness? All of these items are ad-
dressed in a new ABYC standard to be published in 2012
Gasoline boats must not only comply, but the boatbuilder
must install certified components and affix a label visible
from the helm with the company’s name and the statem
Meets U.S. EPA Evap Standards Using Certified Compone
Auto Fill Shutoff
The other really big change is the requirement for auto fil
nozzle shutoff. The fuel-fill nozzle is to shut off in complia
with SAE J 285,
Nozzle Spouts for Liqui
Fuels Intended for Use
with Spark Ignition an
Compression Ignition E
Many have asked why
is included with all of t
other changes that bo
builders will be facing,
and the reasons are as
a) It was determined early on that liquid fuel is detri
tal to the canister (and allows fuel in a place we di
not intend it to be). Activation of the nozzle auto-
shutoff feature was a way to ensure the liquid level
the tank remained where it was supposed to.
b) There has always been a ullage space (air space at
the top of the tank) required for expansion, the aut
shut-off ensures this. (Ullage is specifically the
amount of volume in a tank that is not filled with li
uid. Ullage can be quantified as an absolute quanti
in gallons or cubic feet or it can be quantified as a
percentage of maximum tank capacity.)
c) We needed a way to keep the fill hose free of fuel (
order for it NOT to have to meet the 15 g/m
meation) so, auto shut-off became the answer. (A1
hose is not manufactured in diameters large enou
for fuel fills, so standard A2 hose needs to be em-
ployed here.)