3
Ventilation
WARNING
EXHAUST GAS IS DEADLY—GAS-
OLINE VAPORS ARE EXPLOSIVE! Failure to
provide proper ventilation can result in asphyxi-
ation, fire and explosion. The ventilation system
must meet applicable standards and regula-
tions, including those of the USCG, ABYC and
NFPA.
VENTILATION EXHAUST SYSTEM
The USCG requires the genset be open to the atmo-
sphere or be ventilated by an exhaust blower sys-
tem to prevent dangerous concentrations of gaso-
line vapors and exhaust.
Exhaust Blower System Capacity
Each exhaust blower or combination of blowers
must be rated at an air flow capacity not less than
that computed by the formulas in Table 1.
TABLE 1. EXHAUST BLOWER CAPACITIES (USCG)
NET
COMPARTMENT
VOLUME (V)
(Cubic Feet)
MINIMUM
BLOWER
RATING
(CFM)
MINIMUM
SYSTEM
OUTPUT
(CFM)
Smaller than 34
50
20
Between 34 and 100
V x 1.5
V x 0.6
Larger than 100
(V
÷
2) + 100
(V x 0.2) + 40
V = Net volume of genset compartment and compartments
open thereto. CFM = Cubic Feet per Minute.
Warning Labels
To remind the boat operator to turn on the ventilation
exhaust system before starting the genset, a label
must be affixed next to each genset starting switch,
to the effect that:
WARNING
Gasoline vapors can explode. Be-
fore starting the genset, operate the exhaust
blower for 4 minutes and check the genset
compartment and bilge for gasoline vapors.
Ventilation Ducts
Ventilating air should enter near the bottom of the
compartment at the left side, near the air inlet
(Page 23), and exit near the top at the right side.
This will promote natural convective air flow, good
air exchange and fresh air for combustion and gen-
erator cooling when the exhaust blower system is
not running.
Ventilation Air Inlets
The free-air area of a ventilation air inlet should be at
least twice that of the duct. Use 40 in
2
(258 cm
2
) as
the basis for calculating inlet and outlet air duct
sizes and areas for screens and louvers. Do not use
flush air inlets or louvered transom outlets, which
are easily blocked. Means must be provided to keep
out sea spray.
Ventilation for Cooling
Ventilation is also necessary for genset cooling, es-
pecially just after the boat has been under way. Op-
erating a genset in ambient temperatures above
104
°
F (40
°
C) will result in noticeable loss of power.
Operating a genset in ambient temperatures higher
than 122
°
F (50
°
C) will reduce the life of electrical
components, generator windings, rubber and other
construction materials.
Redistribution or publication of this document,
by any means, is strictly prohibited.
