Ventilation
Powered Ventilation
FEDERAL LAW
183.610 - Powered ventilation 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
II - 183.610
Net compartment volume is the result of subtracting
the volume of permanently installed items such as the engine(s),
fuel tanks, equipment and accessories from the total compartment
volume of the compartment. A discussion of the items that
may or may not be included, and suggestions for accounting
for engines and fuel tanks appears as part of the discussion
under 183.605 of this guideline.
The regulation is not specific about compartments
that adjoin a compartment which qualifies as open to the atmosphere.
The following discussion presents acceptable ways of handling
this problem but they are not necessarily the only ways.
A compartment adjacent and connected to a compartment
that is open to the atmosphere may be considered open to the
atmosphere if:
The total of all open areas directly exposed
to the atmosphere from both compartments is at least 15 square
inches for each cubic foot of the combined net compartment
volumes.
Long narrow compartments should have openings
at each end or along the sides if they are to be considered
open to the atmosphere.
See Figure
4 for diagrams of connecting compartments.
REMOVABLE ENCLOSURES
Fabric weather enclosures are not airtight and
must be opened in order to enter the boat. Upon entering,
any gasoline vapors present should be detectable by means
of their odor. If an open compartment is covered by removable
fabric weather enclosures, the enclosure may be ignored. The
actual ventilation openings should remain outside of the weather
enclosure. Snap-in bulkheads, such as motor well curtains,
are not weather enclosures and may require the enclosed compartment
to be ventilated.
FIGURE
4 - Connecting Compartments Qualifying as “Open to the
Atmosphere”
SCREENS AND LOUVERS
If openings to a compartment are screened or
louvered, the area of the opening is the aggregate net open
area of the screen or louver. The compartment volume is determined
by the average cross section of the compartment in square
feet and multiplied by the length of the compartment in feet.
This computation will give the compartment volume in cubic
feet. For an irregular compartment, the volumes of portions
of the compartment may be computed separately and then the
volumes combined to get the total compartment volume. To get
the net compartment volume, subtract the volume of the installed
items as referred to in 183.605.
The net volume of adjoining compartments may
have to be added to the engine compartment volume. The following
rules apply:
ADD -
If the area of openings between compartments is more than
2% of the area of the separation structure; i.e. bulkheads,
stringers, frames, etc.
DO NOT ADD
- If the area of openings between compartments is equal
to or less than 2% of the area of the separation structure;
i.e. bulkheads, stringers, frames, etc.
The total net volume of the engine compartment
and all other connecting compartment volumes are required
to be ADDED. See Column 1 of Table 183.610. These volumes
are used to determine the required rated blower capacity and
the blower system output. See Columns 2 and 3 of Table 183.610.
RATED BLOWER CAPACITY - TABLE 183.610 COLUMN
2
The air flow capacity rating (Fr) of blowers
is determined by one of the following procedures:
- AMCA Standard 210-74, Figure 12 or UL Standard
1128. The UL Standard is specifically for testing marine
blowers. See the appendix for the reference.
- This information may be found in the information
supplied by the blower manufacturer.
BLOWER SIZE SELECTION
The total rated capacity of the required blower
or blowers (Fr) is based on the net compartment volume (V)
as specified in Table 183.610. One or more blowers may be
used to provide the required capacity. Figure 5 is a graph
of rated blower capacity versus net compartment volume.
Example 1:
The net compartment volume of an engine compartment in a
boat is 20 cubic feet (Below 34; See Table 183.610).
The required rated blower capacity is 50 cubic
feet per minute.
Normally one blower will satisfy the requirement
for this compartment.
Example 2:
The net compartment volume of an engine compartment is 100
cubic feet (34 to 100 cu. ft.; See Table 183.610).
The required rated blower capacity is 150
cubic feet per minute. (1.5 x 100 = 150)
Two blowers could be used to satisfy this
requirement - one rated at 100 cubic feet per minute and
one rated at 50 cubic feet per minute. One 150 cubic feet
per minute blower would satisfy the requirement that Fr
= 1.5 V. Blowers with higher capacity ratings than the minimum
may be used.
Example 3:
The net compartment volume of an engine compartment is 800
cubic feet (over 100 cu. ft.; See Table 183.610). The rated
blower capacity required in this installation is 500 cubic
feet per minute (800/2 + 100 = 500).
One, two or more blowers may be used to satisfy
this requirement. Using readily available marine blowers,
two 200 cubic feet per minute blowers and one 100 cubic
feet per minute blower might be selected. Blowers with higher
capacity ratings than the minimum may be used.
FIGURE
5 - Rated Blower Capacity
TO COMPLY WITH
THE LAW
Answer YES to one of the following:
- Is the blower rated in accordance
with AMCA Standard 210-74, or
- Is the blower rated in accordance
with UL Standard 1128 as evidenced by the display
of the UL Marine label?
If the answer is NO in both cases,
then the boatbuilder must rate the blower in accordance
with one of the above referenced standards. See Appendix.
- Having determined the net compartment
volume in Column 1, is the rated blower capacity of
the blower or blowers selected at least that required
in Column 2, Table 183.610?
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