Volvo Penta 4.3OSi-E, Руководство оператора

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6 7742836 07-2003
Introduction
Factors that affect engine
performance
Power ratings
A great number of environmental factors, such as baromet-
ric pressure, ambient temperature, humidity, the quality of
fuel, and exhaust back pressure can affect engine perfor-
mance. When it comes to quoting and comparing ratings, it
is important that there is a unified set of standards for
measurement.
In September 1989, all major marine engine manufactur-
ers agreed to quote engine power output according to a
common set of conditions. These conditions are referred to
as
ISO 8665. All Volvo Penta engines meet the ISO 8665
standard. This ISO standard outlines the following fixed
values or common conditions for determining the rating of
the engine.
Condition .................................................................... Value
Sea Water ........................................................ 77°F (25°C)
Air Temperature ............................................... 77°F (25°C)
Exhaust back-pressure ............................ 1.45 PSI (10kPa)
Barometric pressure .......................... 14.504 PSI (100 kPa)
Relative humidity .......................................................... 30%
A gasoline engine operates with very little surplus air.
When conditions deviate from the standard values, the
result can be a loss of power at full load. It can also cause
a rise in exhaust emissions due to incomplete fuel com-
bustion.
Marine engines can be rated according to one of several
power standards, but power output itself is quoted in
kilowatts (kW) or horsepower (HP), for a given engine
speed, usually at maximum revolutions per minute (RPM).
How load conditions affect the speed of
a planing hull
The overall weight of the boat is another important factor in
performance. Any increase in boat weight will slow down
the boat speed, particularly on boats with planing and
semi-planing hulls.
For example, a new boat tested with fuel and water tanks
only half filled, and without any load, can easily drop 2 to 3
knots in speed when tested fully fuelled and loaded with all
normal equipment and supplies for safe and comfortable
cruising. This is because the propeller installed originally is
frequently one that is designed to give maximum speed
when the boat is new. For this reason it is often advisable
to reduce the propeller pitch by as much as an inch or
more in order to counter the effects of the increase in
overall weight encountered in normal cruising, particularly
in hotter climates. Although this will reduce top speed
somewhat, overall ride conditions will improve and you
should achieve greatly enhanced acceleration.
In considering the influence of weight, it is worth remem-
bering that fiberglass boats absorb a significant amount of
water into their hulls while left afloat for any
length of time
and so become progressively heavier. Another negative
influence on boat performance is marine growth beneath
the waterline - a problem that is often overlooked.
“Station Wagon” effect
As long as we continue to use combustion technology for
engines, there will be exhaust emissions. Despite the
substantial reductions achieved in modern engines, as
gasoline burns exhaust emissions and fumes will always
be given off.
But there is also another effect. Any shear-bodied object
moving forward will create a phenomenon we call “Station
Wagon effect.” Due to a difference in air pressure, the
airflow behind such an object will have a tendency to draw
dirt and exhaust emissions back into the object. (You’ll
frequently see evidence of this in the excess of road grime
that is drawn back onto the rear windows of cars.) A boat
with a sheer, broad transom and high superstructure
creates its own station wagon effect. This recirculating air
has a tendency to draw exhaust fumes and water spray up
toward the after-deck. Often people will make the mistake
of opening a ventilator or port hole in order to remove the
fumes, but it has the opposite effect — more fumes are
drawn in, and conditions merely become worse. In high
concentrations these fumes may be hazardous. If you
suspect that your boat exhibits this “station wagon” effect,
please contact your Volvo Penta dealer.
WARNING! Do not run the engine while there are
people located on the swim platform.
DANGER! DO NOT tow anyone using water sports
equipment (such as skis and inner tubes) closer than
ten feet (10’) from the boat. DO NOT, under any circum-
stances, allow people to “teak surf” or “drag surf” using
the swim platform as a means of being pulled along.
Carbon Monoxide poisining may result in serious injury
or death.