Section 6. The exhaust of every internal combustion engine on any motorboat shall be effectively muffled by a muffler or underwater exhaust of a type or types approved by and used in conformity with the rules and regulations of the director. The use of cutouts is prohibited, except for motorboats competing in a race previously approved by the director, and for such motorboats while on trial runs during a period not to exceed forty-eight hours immediately preceding such race, and for such motorboats while competing in official trials for speed records during a period not to exceed forty-eight hours immediately following such race.