46 CFR § 119.425 - Engine exhaust cooling.
(a) Except as otherwise provided in this paragraph, all engine exhaust pipes must be water cooled.
(2) Horizontal dry exhaust pipes are permitted only if:
(i) They do not pass through living or berthing spaces;
(ii) They terminate above the deepest load waterline;
(iii) They are so arranged as to prevent entry of cold water from rough or boarding seas;
(iv) They are constructed of corrosion resisting material at the hull penetration; and
(b) The exhaust pipe cooling water system must comply with the requirements of this paragraph.
(1) Water for cooling the exhaust pipe must be obtained from the engine cooling water system or a separate engine driven pump.
(2) Water for cooling an exhaust pipe, other than a vertical exhaust, must be injected into the exhaust system as near to the engine manifold as practicable. The water must pass through the entire length of the exhaust pipe.
(3) The part of the exhaust system between the point of cooling water injection and the engine manifold must be water-jacketed or effectively insulated and protected in compliance with §§ 116.400(b) and 116.970 of this chapter.
(4) Each vertical exhaust pipe must be water-jacketed or suitably insulated between the engine manifold and the spark arrester required by § 119.430(g) of this part.
(5) When the exhaust cooling water system is separate from the engine cooling water system, a suitable warning device, visual or audible, must be installed at the operating station to indicate any reduction in normal water flow in the exhaust cooling system.
(6) A suitable hull strainer must be installed in the circulating raw water intake line for the exhaust cooling system.
(c) Engine exhaust cooling systems built in accordance with the requirements of American Boat and Yacht Council (ABCY) P-1, “Installation of Exhaust Systems for Propulsion and Auxiliary Engines,” will be considered as meeting the requirements of this section.
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