A boat less than 12 meters (39.4 feet) in length must have which of the following aboard?

A vessel that is less than 12 meters in length is required to carry a sound signaling device. This requirement exists because sound signaling devices are essential for safe navigation and communication, especially in situations where visibility may be limited or in areas where other vessels may be nearby. Such devices, which can include whistles, horns, or bells, help alert others to your presence and intentions on the water, reducing the risk of collisions.

The other options, while important safety considerations, are not specifically mandated for boats of this size under Mississippi boating regulations. For instance, a VHF radio or cell phone is useful for communication, but it is not a requirement for all smaller boats. Similarly, while a marine sanitation device is necessary for certain types of vessels, it typically applies to boats with specific sanitation system needs. Finally, while it's ideal to have a seat for every passenger to ensure comfort and safety, this is not a legislative requirement based solely on vessel size. Thus, the sound signaling device stands out as a crucial safety gear specifically tailored to the regulations governing smaller boats.