For a vessel under 39.4 feet long, what light might serve as a combination of other lights?

A vessel under 39.4 feet long can utilize an all-round white light as a combination of other lights for visibility in various conditions. The all-round white light is designed to provide 360-degree illumination, which allows the vessel to be seen from all angles. This is particularly effective for small vessels that may not have the necessary space or resources to accommodate multiple separate lights.

This single light can serve multiple purposes, such as signifying the vessel's presence and its status. For instance, it can indicate that the vessel is either on anchor or underway, depending on its visibility and application during different times of the day.

While the other light types, such as masthead light, sternlight, and sidelights, serve specific and separate functions necessary for larger vessels or specific operating conditions, the all-round white light effectively merges their roles into one for smaller vessels, simplifying the lighting requirements while ensuring safety on the water.