Dave Gerr - Boat Mechanical Systems Handbook-How to Design, Install, and Recognize Proper Systems in Boats

Example:If we assume After Burnerhas
V-8 gas engines, we would determine the
gasoline blower requirements as follows:

Net compartment volume= 290 cu. ft. or

7.89 m^3 (assuming openings on the

bulkheads are less than 2 percent of

their area)

From column 2 of Table 16-2, we find

Net compartment volume is over 100 cu.

ft. or over 2.83 m^3

Blower capacity= Fr= (290 cu. ft. ÷ 2)+

100 = 245 cfm

or

Blower capacity= Fr= (7.89 m^3 ÷2)+

2.83= 6.77 m^3 /min.

In this case, the powered-blower require-
ments would be met with a single 4-inch
diameter, 250 cfm (10.2 cm dia., 6 m^3 /min.)

squirrel-cage exhaust blower. Note, though,

that we already specified a pair of these using

the engine vent sizing rule earlier. In almost

all cases, the blower size from the engine

vent sizing rule will exceed the minimum re-

quired by the CFR. But you should always

check to be sure. Note also that on diesel

craft, with installed engine power less than

500 hp (373 kW),the blowers are recom-

mended but optional per the engine vent siz-

ing rule. On gasoline boats, a blower to meet

CFR 183.610 is required—always.

Of course, if you need extra blower ca-

pacity, you can use two or more blowers and

duct systems to achieve the required total

capacity.

Gasoline Blower System

Output

As we saw for our calculation of the required

blower size for the below-deck stateroom

(Chapter 14), ducting, grilles, and so on

reduce the efficiency of the ventilation

Chapter 16:Ventilation of Machinery Spaces

TABLE 16-2.GASOLINE BLOWER REQUIREMENT TABLE (CFR 183.610)

English Units

Column 1 Column 2 Column 3

Net Compartment Volume (V) Rated Blower Capacity (Fr) Blower System Output (Fo)

cu. ft. cfm cfm

less than 34 Fr= 50 Fo= 20

34 to 100 Fr= 1 .5V Fo= 0 .6V

over 100 Fr= (V ÷ 2)+ 100 Fo= 0 .2V+ 40

Metric Units

Column 1 Column 2 Column 3

Net Compartment Volume (V) Rated Blower Capacity (Fr) Blower System Output (Fo)

m^3 m^3 /min. m^3 /min.

less than 0. 96 Fr= 1. 41 Fo= 0. 57

0 .96 to 2. 83 Fr= 1 .5V Fo= 0 .6V

over 2. 83 Fr= (V ÷ 2)+ 2. 83 Fo= 0 .2V+ 1. 13

NOTE:The net compartment volume includes all the volumes of all compartments that open into
the compartment that contains the engine, unless the area the engine compartment opens to is
“open to the atmosphere,”as described above;however, long, narrow compartments need to
have openings at both ends or along much of the sides to qualify as “open to the
atmosphere.”
NOTE:“The 2 Percent Rule”:Adjacent compartments do notneed to be included in the net
compartment volume if the openings in the bulkhead or panel between the compartments
comprise less than 2 percent of the total surface area of the bulkhead or panel.