Volvo Penta SX-A Operator's Manual page 113

47701898 12-2010
Less than Optimal Performance
A great number of environmental factors, such as baro-
metric pressure, ambient temperature, humidity, the
quality of fuel, and exhaust back pressure can affect
engine performance. All Volvo Penta engines are
tested and certified using the following fixed values or
common conditions for determining the rating of the
engine.
Condition
Air temperature . . . . . . . . . . . . . .
Barometric pressure . . . . . . . . . . 100 kPa (14.504 PSI)
Relative humidity . . . . . . . . . . . . .
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 combustion.
Hull Weight
The overall weight of the boat is an important factor in
performance. Any increase in boat weight will slow
down the boat speed, particularly on boats with planing
and semi-planing hulls. To minimize this problem, elim-
inate all excess weight from the boat.
In considering the influence of weight, it is worth
remembering 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 water line–a problem that
is often overlooked.
The propeller originally installed 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 some-
what, overall ride conditions will improve and you
should achieve greatly enhanced acceleration.
If you feel that your boat performance has declined
over time, we recommend that you visit an authorized
Vovlo Penta dealer to discuss the issue. Your dealer
can assist you with selecting the correct propeller size,
gear ratio, and horsepower for your boat, based on
your current operating conditions.
Troubleshooting
Value
25°C (77°F)
30%
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