Muffler, defined - noise level regulation, muffler system required, ...
Mo. Rev. Stat. § 306.147
in effect306.147. Muffler, defined — noise level regulation, muffler system required, certification of manufacturer — exceptions — on-site test to measure noise levels, penalty — application of section. — 1. As used in this section, the term "muffler" means a sound suppression device or system designed and installed to abate the sound of exhaust gases emitted from an internal combustion engine and which prevents excessive or unusual noise.
2. Effective January 1, 1996, a person shall not manufacture, sell or offer for sale or operate in this state any motorboat manufactured after that date that exceeds the noise level of 90dB(A) when subjected to a stationary sound level test as prescribed by SAE J2005. All motorboats manufactured prior to January 1, 1996, shall not exceed eighty-six decibels on an A-weighted scale when subjected to a sound level test as prescribed by SAE J34 when measured from a distance of fifty or more feet from the motorboat.
3. No person shall remove, alter or otherwise modify in any way a muffler or muffler system in a manner which will prevent it from being operated in accordance with this section. Nothing in this section shall preclude a person from removing, altering or modifying a muffler or muffler system so long as the muffler or muffler system continues to comply with subsection 2 of this section. This section shall not be construed so as to prohibit the use of any exhaust system or device, including but not limited to those not discharging water with exhaust gases, so long as the device or system is in compliance with subsection 2 of this section.
4. No motorboat shall be equipped with any electrical or mechanical device or switch that when manipulated in any manner would allow the muffler or exhaust system to emit a noise level that exceeds the maximums in subsection 2 of this section.
5. Effective January 1, 1996, a person shall not manufacture, nor shall any person sell or offer for sale any motorboat which is manufactured after January 1, 1996, which is equipped with a muffler or muffler system which does not comply with this section. The subsection shall not apply to power vessels designed, manufactured and sold for the sole purpose of competing in racing events and for no other purpose. Any such exemption or exception shall be documented in every sale agreement and shall be formally acknowledged by signature on the part of both the buyer and the seller. Copies of such agreement shall be maintained by both parties. A copy of such agreement shall be kept on board whenever the motorboat is operated. Any motorboat sold under this exemption may only be operated on the waters of this state in accordance with subsection 7 of this section.
6. As of January 1, 1996, every manufacturer which delivers a new motorboat for sale in this state shall certify, if the purchaser or dealer makes a request in writing, that the decibel level of the motorboat engine, muffler and exhaust system, as delivered to any licensed dealer in this state, does not exceed the noise level of 90dB(A) when subjected to a stationary sound level test as prescribed by SAE J2005. Such certificate of decibel level from the manufacturer shall be given by the dealer to the purchaser of the new motorboat if the motorboat is sold for use upon the waters of this state. The purchaser shall sign a statement acknowledging receipt of the certificate of decibel level which shall be supplied by the dealer. The dealer shall represent by affidavit whether or not the engine or muffler system of the new motorboat being sold has been altered or modified in any way.
7. The provisions of this section shall not apply to motorboats registered and actually participating in a racing event or tune-up periods for such racing events or to a motorboat being operated by a boat or engine manufacturer for the purpose of testing or development. The operator of any motorboat operated upon the waters of this state for the purpose of a tune-up for a sanctioned race or for testing or development by a boat or engine manufacturer shall at all times have in such operator's possession and produce on demand by a law enforcement officer a test permit issued by the water patrol division. For the purpose of races or racing events, such race shall only be sanctioned when conducted in accordance with and approved by the United States Coast Guard or this state.
8. Any officer authorized to enforce the provisions of this section who has probable cause to believe that a motorboat is not in compliance with the noise levels established in this section may direct the operator of such motorboat to submit the motorboat to an on-site test to measure noise levels, with the officer on board if such officer chooses, and the operator shall comply with such request. The owner of any motorboat which violates any provision of this section shall have sixty days from the date of the violation to bring the motorboat into compliance with the provisions of this section. Thereafter, it shall be the owner's responsibility to have the motorboat tested by the water patrol division. If the motorboat fails the water patrol division test, the owner shall immediately moor the motorboat and shall keep the motorboat moored until the water patrol division certifies that the motorboat is in compliance with the provisions of this section. Any person who fails to comply with a request or direction of an officer made pursuant to this subsection is guilty of a class C misdemeanor. Nothing in this subsection shall be construed to limit the officer's ability to enforce this section and to issue citations to the owner or operator of any motorboat during the sixty-day compliance period.
9. Any officer who conducts motorboat sound level tests as provided in this section shall be qualified in motorboat noise testing by the department of public safety. Such qualifications shall include but may not be limited to the selection of the measurement site, and the calibration and use of noise testing equipment in accordance with the testing procedure prescribed by SAE J2005 and SAE J34.
10. Unless otherwise indicated, any person who knowingly violates this section is guilty of an infraction for a first offense with a penalty not to exceed one hundred dollars, is guilty of an infraction for a second offense with a penalty not to exceed two hundred dollars, and is guilty of an infraction for a third or subsequent offense with a penalty not to exceed three hundred dollars.
11. This section shall not apply to motorboats not intended for use in this state.
(L. 1995 H.B. 217, A.L. 1997 H.B. 379, A.L. 2005 H.B. 353, A.L. 2008 H.B. 1715)
Source: Open US Law by Vaquill AI (CC BY 4.0)URL: https://revisor.mo.gov/main/OneSection.aspx?section=306.147Fetched: 10/17/2026