33 C.F.R. § 183.610 – Powered ventilation system.

(a) Each compartment in a boat that has a permanently installed gasoline engine with a cranking motor must:
1. (1) Be open to the atmosphere, or
2. (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 thereto (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. (1) Is located as close as practicable to each ignition switch;
2. (2) Is in plain view of the operator; and
3. (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.