Backdrafting (Station Wagon Effect) - Four winns Horizon Owner's Manual

A boat operator should be aware that carbon monoxide is
emitted from any boat's exhaust. The operation, moor-
ing, and anchoring in an area containing other boats may
be in an atmosphere containing CO not of the operator's
making. An operator likewise needs to be aware of the
effect of his actions on other boats. Of prime concern is
the operation of an auxiliary generator with boats moored
along side each other. Be aware of the effect your ex-
haust may have on other vessels and be aware that the
operation of other vessel's equipment may affect the car-
bon monoxide concentration on your vessel. See Fig-
ure B8.
Figure B8: The effect of boats moored along side.
J. Backdrafting (Station Wagon Effect)
Backdrafting or the "station wagon effect" is caused by
air movement over or around a boat creating a low pres-
sure area of suction area around the stern which can
increase CO level on the boat. Backdrafting can be af-
fected by relative wind direction, boat speed, and boat
trim angle. See Figure B9 Backdrafting - Airflows Over
Boat and Behind Transom".
Under certain speed and operating conditions the low
pressure area may form in other regions and permit car-
bon monoxide to enter the hull through openings that
are not on the back of the vessel. Boat factors which
may affect CO concentration:
Figure B9: Backdrafting - Air flows over boat and
behind transom.
1. Inefficient trim angle. See Figure B10.
2. Excessive or unequally distributed weight.
180/190/200 Horizon
Owner's Manual
08/01
Figure B10: Inefficient trim angles.
3. Canvas Configurations - Under various conditions,
adding or removing canvas may raise or lower CO
levels. See Figures B9, B10 & B12.
Exhaust Fumes!
Hull exhaust from your boat can cause exces-
sive accumulation of poisonous carbon mon-
oxide gas within cockpit areas when using pro-
tective weather coverings (while underway or
while stationary). Provide adequate ventilation
when the canvas top, side curtains and/or back
(aft) curtains are in their closed protective po-
sitions. (See Preface for actual warning label
regarding carbon monoxide and weathering
cover/canvas.)
4. Opening and closing ports, hatches, doors, and win-
dows may raise or lower CO levels on board a boat.
See Figures B11 and B12.
Figure B11: Desired air flow through the boat.
Figure B12: The effect of canvas configurations.
Section B
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