(a) For the purpose of § 183.620, “natural ventilation” means an airflow in a compartment in a boat achieved by having:
(1) A supply opening or duct from the atmosphere or from a ventilated compartment or from a compartment that is open to the atmosphere; and
(2) An exhaust opening into another ventilated compartment or an exhaust duct to the atmosphere.
(b) Each exhaust opening or exhaust duct must originate in the lower third of the compartment.
(c) Each supply opening or supply duct and each exhaust opening or exhaust duct in a compartment must be above the normal accumulation of bilge water.
(d) Except as provided in paragraph (e) of this section, supply openings or supply ducts and exhaust openings or exhaust ducts must each have a minimum aggregate internal cross-sectional area calculated as follows:
A = 5 ln (V/5);
where:
(1) A is the minimum aggregate internal cross-sectional area of the openings or ducts in square inches;
(2) V is the net compartment volume in cubic feet, including the net volume of other compartments connected by openings that exceed 2 percent of the area between the compartments; and
(3) ln (V/5) is the natural logarithm of the quantity (V/5).
(e) The minimum internal cross-sectional area of each supply opening or duct and exhaust opening or duct must exceed 3.0 square inches.
(f) The minimum internal cross-sectional area of terminal fittings for flexible ventilation ducts installed to meet the requirements of paragraph (d) of this section must not be less than 80 percent of the required internal cross-sectional area of the flexible ventilation duct.
[CGD 76-082, 44 FR 73027, Dec. 17, 1979; 45 FR 7544, Feb. 4, 1980]