Explanation: Marine VHF transmitters utilize Narrowband Frequency Modulation (NBFM). The maximum allowable deviation for this service is regulated to ensure efficient use of the radio spectrum and prevent interference with adjacent channels. According to FCC Part 80 regulations for maritime services, which align with international standards, the maximum frequency deviation for voice transmissions on marine VHF channels is $\pm 5$ kHz. This standard allows for a reasonable audio bandwidth while keeping the transmitted signal within its allocated 25 kHz channel spacing. Wider deviations, such as 7.5 kHz, 10 kHz, or 12 kHz, would be characteristic of Wideband FM, which occupies significantly more bandwidth and would cause interference on the closely spaced marine channels.