Iowa Code § 462A.11: Muffling devices.

The exhaust of every internal combustion engine used on any motorboat shall be effectively muffled by equipment so constructed and used as to muffle the total vessel noise in a reasonable manner in accordance with rules adopted by the commission. The use of cut-outs is prohibited, except for motorboats competing in a regatta or boat race approved as provided in section 462A.16 and for such motorboats while on trial run during a period from 8:00 a.m. to 6:00 p.m. not to exceed twenty-four hours immediately preceding such regatta or race.