How is a power-driven vessel distinguished from another vessel under 50m?

Answer: B — By having two masthead lights

A power-driven vessel is uniquely identified by certain lighting configurations as specified in the COLREGs to ensure clear identification during navigation. One key distinguishing feature is the requirement for power-driven vessels to display two masthead lights. These lights are placed vertically with one above the other and are typically white. This distinct lighting arrangement helps differentiate power-driven vessels from sailing vessels and other types of craft, particularly at night or in reduced visibility. Understanding why the other options do not serve as a distinguishing feature is important. The presence of additional port lights or variations in sternlight color do not provide a standardized means of identification across all power-driven vessels. Similarly, an all-around light is typically used by various types of vessels not limited to power-driven ones, and thus does not serve as a definitive identifier. The use of two masthead lights is explicitly outlined in the regulations and is a critical element for nighttime navigation, making it the correct distinguishing characteristic for power-driven vessels compared to others under 50 meters.