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Figure A7: The effect of boats moored along side
K. Backdrafting (Station Wagon Effect)
Backdrafting or the "station wagon effect" is caused
by air movement over or around a boat creating a low
pressure area or suction area around the stern that
can increase CO level on the boat. Backdrafting can
be affected by relative wind direction, boat speed,
and boat trim angle. See Figure A8 Backdrafting –
Airflows Over Boat and Behind Transom".
Figure B8: Backdrafting - Air flows over boat and
behind transom
Under certain speed and operating conditions, the low
pressure area may form in other regions and permit
carbon monoxide to enter the hull through openings
that are not on the back of the boat. Boat factors
which may affect CO concentration:
1. Intentional or unintentional excessive trim angle
causing high bow angle. See Figure A9.
2. Excessive or unequally distributed weight.
Figure A9: Inefficient trim angles
3. C a n v as c o nfi g ur a t i o ns – Un d er var i o us c o n d it i o n s,
adding or r emov ing canvas may raise or lower CO
l evels. See Fi gures A8, A9 & A11.
Boating Safety & Information - Section A
EXHAUST FUMES!
Hull exhaust from your boat can cause ex-
cessive accumulation of poisonous carbon
monoxide gas within cockpit areas when using
protective weather coverings (while underway
or while stationary). Provide adequate ventila-
tion when the canvas top, side curtains and/or
back (aft) curtains are in their closed protective
positions.
4. Opening and closing ports, hatches, doors, and
windows may raise or lower CO levels on board
a boat. When airflow is moving forward inside the
boat, CO may be entering the boat. See Figures
A10 and A11.
Figure A10: Desired air flow through the boat
Figure A11: The effect of canvas configurations
5. Operating a boat at slow speeds with a following
wind should be avoided. Consider changing direc-
tion, adjusting speed, or both. See Figure
A12.
Figure A12: Operating at Slow Speed
with Following Wind
Owner's Manual Page 25
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