46 CFR §182.420

1. (a)Except as otherwise provided in paragraphs (b), (c), (d), and (e) of this section, all engines must be water cooled and meet the requirements of this paragraph.
   1. (1)The engine head, block, and exhaust manifold must be water-jacketed and cooled by water from a pump that operates whenever the engine is operating.
   2. (2)A suitable hull strainer must be installed in the circulating raw water intake line of an engine cooling water system.
   3. (3)A closed fresh water system may be used to cool the engine.
2. (b)An engine water cooling system on a vessel of not more than 19.8 meters (65 feet) in length, carrying not more than 12 passengers, may comply with the requirements of ABYC P-4 (incorporated by reference; see 46 CFR 175.600) instead of the requirements of paragraph (a) of this section.
3. (c)On a vessel of not more than 19.8 meters (65 feet) in length carrying not more than 12 passengers, a propulsion gasoline engine may be air cooled when in compliance with the requirements of ABYC Project P-4.
4. (d)An auxiliary gasoline engine may be air cooled when:
   1. (1)It has a self-contained fuel system and it is installed on an open deck; or
   2. (2)On a vessel of not more than 19.8 meters (65 feet) in length carrying not more than 12 passengers, it is in compliance with the requirements of ABYC P-4.
5. (e)A propulsion or auxiliary diesel engine may be air cooled or employ an air cooled jacket water radiator when:
   1. (1)Installed on an open deck and sufficient ventilation for machinery cooling is available;
   2. (2)Installed in an enclosed or partially enclosed space for which ventilation for machinery cooling is provided, which complies with the requirement of § 182.465(b), and other necessary safeguards are taken so as not to endanger the vessel; or
   3. (3)Installed on a vessel of not more than 19.8 meters (65 feet) in length carrying not more than 12 passengers, in compliance with the requirements of ABYC Project P-4.