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Exhaust Noise Muffling, Ventilation, Backfire Control

Exhaust Muffling

The exhaust of every internal combustion engine used on any motorboat needs to always be effectively muffled in accordance with Oregon Revised Statute 830.260 and Oregon Administrative Rule 250-010-0121.

The term "effectively muffled" means the exhaust system contains a mechanical device or appliance designed, constructed, and used to reduce the exhaust noise emissions of a motorboat below the maximum noise levels. Such a device or appliance must be integral to the motorboat's exhaust system. Water muffling systems which meet this standard are those which incorporate a marine exhaust manifold.    

(A weighted decibel, abbreviated dBA, is an expression of the relative loudness of sound in the air as perceived by the human ear.)

A person shall operate a motorboat on the waters of this state in such a manner that does not exceed the following noise level: (a) For engines manufactured before January 1, 1993, a maximum noise level of 90 dBA when subjected to a stationary test; (b) For engines manufactured after January 1, 1993, a maximum noise level of 88 dBA when subjected to a stationary test; (c) A maximum noise level of 84 dBA as measured from the shoreline. This regulation does not apply to boats competing in permitted regattas, races, or time trials or to boats operating in designated testing areas pursuant to ORS 830.350.

The Marine Board has the authority to regulate motorboat noise from boat motors. However, keep in mind that stereo noise can also be loud. Play nice and respect the recreation of others. Keep the stereo volume down, especially near residential areas if operating for longer durations in the same place.



In motorized boats, flammable gases can gather and have the potential to create a powerful explosion. A ventilation system is required for boats (with a permanently installed gasoline engine) that use gasoline for propulsion, mechanical power, or electrical generation. 

Natural Ventilation Systems:
A minimum of two ventilator ducts (1 intake, 1 exhaust duct) fitted with cowls (hooded opening) installed to remove stagnant fumes. 

Powered Ventilation Systems:
Required on boats built after July 31, 1980, with installed fuel tanks or an enclosed engine. Consists of 1 or more exhaust blowers.  

TIP: Ensure intake ducts are located above the normal accumulation of bilge water. Turn on the ventilation system (blower) for FOUR minutes before you start the engine, to ensure all gasoline vapors have cleared.

Carburetor Backfire Flame Control Device (Arrestor)Backfire flame control device graphic

OAR 250-010-0122 

Gasoline engines installed in a boat after April 25, 1940, except outboard motors, must be equipped with an acceptable means of backfire flame control. The device must be attached to the air intake with a flame-tight connection. The device is required to be U.S. Coast Guard approved or follow SAE-J-1928 or UL 1111 standards and be marked. Devices are designed to prevent gasoline vapors from igniting if the engine backfires. Make a point to include inspecting the device at the same time as your fire extinguisher. Clean this device periodically. During cleaning, make sure the device is tightly fastened and check for damage.