Read the following from this site (
http://www.uscgboating.org/regulations/fedreg.htm ):
§ 183.610 Powered ventilation system.
(a) Each compartment in a boat that
has a permanently installed gasoline
engine with a cranking motor must:
(1) Be open to the atmosphere, or
(2) Be ventilated by an exhaust blower
system.
(b) Each exhaust blower or combination
of blowers must be rated at an air
flow capacity not less than that computed
by the formulas given in Table
183.610, Column 2. Blower rating must
be determined according to AMCA
Standard 210–74, Figure 12, or UL
Standard 1128.
TABLE 183.610 Col. 1
1 Col. 2 2 Col. 3 3
Below 34 ..... Fr=50 ........................ Fo=20
34 to 100 ..... Fr=1.5V ..................... Fo=0.6V
Over 100 ..... Fr=V/2+100 ............... Fo=0.2V+40
1 Net compartment volume of engine compartment and
compartments open there to (V) cubic feet.
2 Rated blower capacity (Fr) cubic feet per minute.
3 Blower system output (Fo) cubic feet per minute.
(c) Each exhaust blower system required
by paragraph (a)(2) of this section
must exhaust air from the boat at
a rate which meets the requirements of
Table 183.610, Column 3 when the engine
is not operating.
(d) Each intake duct for an exhaust
blower must be in the lower one-third
of the compartment and above the normal
level of accumulated bilge water.
(e) More than one exhaust blower
may be used in combination to meet
the requirements of this section.
(f) Each boat that is required to have
an exhaust blower must have a label
that:
(1) Is located as close as practicable
to each ignition switch;
(2) Is in plain view of the operator;
and
(3) Has at least the following information:
WARNING—GASOLINE VAPORS CAN EXPLODE.
BEFORE STARTING ENGINE OPERATE
BLOWER FOR 4 MINUTES AND
CHECK ENGINE COMPARTMENT BILGE
FOR GASOLINE VAPORS.
§ 183.620 Natural ventilation system.
(a) Except for compartments open to
the atmosphere, a natural ventilation
system that meets the requirements of
§ 183.630 must be provided for each compartment
in a boat that:
(1) Contains a permanently installed
gasoline engine;
(2) Has openings between it and a
compartment that requires ventilation,
where the aggregate area of those
openings exceeds 2 percent of the area
between the compartments, except as
provided in paragraph (c) of this section;
(3) Contains a permanently installed
fuel tank and an electrical component
that is not ignition protected in accordance
with § 183.410(a);
(4) Contains a fuel tank that vents
into that compartment; or
(5) Contains a non-metallic fuel tank:
(i) With an aggregate permeability
rate exceeding 1.2 grams of fuel loss in
24 hours per cubic foot of net compartment
volume, or
(ii) If the net compartment volume is
less than one cubic foot, having a permeability
rate exceeding 1.2 grams of
fuel loss in 24 hours.
NOTE: Reference fuel ‘‘C’’ at 40 degrees Celsius
plus or minus 2 degrees Celsius from
ASTM standard D 471 (incorporated by reference,
see § 183.5) is to be used in determining
the permeability rate.
(b) Each supply opening required in
§ 183.630 must be located on the exterior
surface of the boat.
(c) An accommodation compartment
above a compartment requiring ventilation
that is separated from the
compartment requiring ventilation by
a deck or other structure is excepted
from paragraph (a)(2) of this section.
[CGD 76–082, 44 FR 73027, Dec. 17, 1979, as
amended by CGD 76–082(a), 46 FR 27645, May
21, 1981; CGD 85–059, 51 FR 37577, Oct. 23, 1986;
USCG–1999–5832, 64 FR 34716, June 29, 1999;
USCG–1999–5151, 64 FR 67176, Dec. 1, 1999]
§ 183.630 Standards for natural ventilation.
(a) For the purpose of § 183.620, ‘‘natural ventilation ’’ means an airflow in a compartment in a boat achieved by having:
§ 183.701 33 CFR Ch. I (7–1–04 Edition)
(1) A supply opening or duct from the
atmosphere or from a ventilated compartment
or from a compartment that
is open to the atmosphere; and
(2) An exhaust opening into another
ventilated compartment or an exhaust
duct to the atmosphere.
(b) Each exhaust opening or exhaust
duct must originate in the lower third
of the compartment.
(c) Each supply opening or supply
duct and each exhaust opening or exhaust
duct in a compartment must be
above the normal accumulation of
bilge water.
(d) Except as provided in paragraph
(e) of this section, supply openings or
supply ducts and exhaust openings or
exhaust ducts must each have a minimum
aggregate internal cross-sectional
area calculated as follows:
A=5 ln (V/5);
where:
(1) A is the minimum aggregate internal
cross-sectional area of the openings or
ducts in square inches;
(2) V is the net compartment volume in cubic
feet, including the net volume of other
compartments connected by openings that
exceed 2 percent of the area between the
compartments; and
(3) ln (V/5) is the natural logarithm of the
quantity (V/5).
(e) The minimum internal cross-sectional
area of each supply opening or
duct and exhaust opening or duct must
exceed 3.0 square inches.
(f) The minimum internal cross-sectional
area of terminal fittings for
flexible ventilation ducts installed to
meet the requirements of paragraph (d)
of this section must not be less than 80
percent of the required internal crosssectional
area of the flexible ventilation
duct.
[CGD 76–082, 44 FR 73027, Dec. 17, 1979; 45 FR
7544, Feb. 4, 1980]
The way I read all of that:
1. A power vent is only required if the compartment houses the engine. First part of 183.610. If it doesn't then the next section on natural ventilation could or could not apply according to that section.
2. If the fuel tank itself is vented to the outside like in Paul's case the compartment itself might not need to be vented at all. 183.620 item (4) that says it is needed if the tank vents into the compartment.
3. And Chris to answer your question I could find nothing about cabins, but if you read 183.620 (2) and apply that to the cabin . If the compartment that contains a fuel tank "has to be vented" and if the cabin is attached to that compartment and Has openings between the two where the aggregate area of those openings exceeds 2 percent of the area between the compartments then the cabin would have to also be vented according to 183.630.
Everyone should read these regs and draw their own conclusion. Personally I still believe that a vented (tank itself vented) permanent gas tank is safer than what most of us are doing with portable tanks with vents on them that off gas and even at times emit liquid gas.
Chris how do you tilt your outboard up with even a 1 gallon tank in the well? I can't. Also I'm aware that you use very little gas, but what if you are on say a longer cruise and you had an equipment failure pertaining to the sails, mast or rigging and were force to motor home. Is 1-2 gallons always going to get your there?
c ya,
Sum
