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

area for natural or passive ventilation of a

gasoline-engine compartment (or for fuel or

portable-engine compartments that require

ventilation) under CFR 183.630.

Formula 16-5. Minimum Allowable

Cross-Section Area for Natural

Ventilation

A= 5 × Ln(V cu. ft. ÷ 5)

or

A= 63 + [32.3× Ln(V m^3 )]

Where

A= minimum vent cross-section area, in

sq. in. or cm^2

Ln= the natural logarithm (natural log

or log to base e) of the number

V= net compartment volume, in cu. ft.

or m^3

NOTE: You can find the natural log of any

number on an inexpensive scientific calcula-

tor. Simply hit the natural-log key (usually

“ln”), enter the number you got by dividing

volume by 5, and hit Enter. Don’t use the

“log” key, as that’s for the log to the base 10,

not the natural log.

This formula is for the area of the intake

and outlet vent area combined.

Example:Returning to our After Burner,

we would find the required natural or passive

ventilation area as

Net compartment volume= 290 cu. ft.

(7.89 m^3 )

5 × Ln(290 cu. ft. ÷ 5)= 20.3 sq. in. minimum

cross-section area

or

63 + [32.3× Ln(7.89 m^3 )]= 130 cm^2 minimum

cross-section area

Checking Table 14-3 from Chapter 14,

we see that a pair of 4-inch-diameter (10.2 cm)

vents would do the job nicely, at 12.6 sq. in.

(81.1 cm^2 ) each and 25.2 sq. in. (162.2 cm^2 )

total. Once again, we see that the ventilation

area from the engine vent sizing rule greatly

exceeds this minimum requirement under

the CFR. For After Burner, we had found

PART FIVE:VENTILATION, AIR-CONDITIONING, AND HEATING

Figure 16-6.
Ventilated
compartments
(Courtesy ABYC)

Formula 16-5.