33 CFR §183.620

1. (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. (1)Contains a permanently installed gasoline engine;
   2. (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. (3)Contains a permanently installed fuel tank and an electrical component that is not ignition protected in accordance with § 183.410(a);
   4. (4)Contains a fuel tank that vents into that compartment; or
   5. (5)Contains a non-metallic fuel tank:
      1. (i)With an aggregate permeability rate exceeding 1.2 grams of fuel loss in 24 hours per cubic foot of net compartment volume, or
      2. (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.
2. (b)Each supply opening required in § 183.630 must be located on the exterior surface of the boat.
3. (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.