What is the primary reason most recreational vessels under 20 meters do not need to carry a marine radio?

The primary reason most recreational vessels under 20 meters do not need to carry a marine radio is that they are below the size threshold set by regulations. This size threshold is established by maritime authorities to determine which vessels are required to have certain safety equipment on board. Vessels under 20 meters generally operate well within the limits of local waters and often do not voyage into deeper, more distant areas where marine radios become essential for safety and communication.

While sometimes alternative communication devices, legal requirements, and typical usage may be factors, the defining underlying aspect is the regulatory framework that exempts smaller boats from this requirement solely based on their length. This means that while having a marine radio is advisable for safety, it is not mandated for vessels under this specified size.