What are the requirements for spacing of lights on a vessel of 20m or more in length when the rules require two or three lights in a vertical line?

The requirements for spacing of lights on a vessel that is 20 meters or more in length, especially when multiple lights are required in a vertical line, are focused on ensuring visibility and clarity in the vessel's identification and signaling to other mariners. When the regulations state that the lights must be equally distributed across the vertical line, it ensures that all lights are distinctly visible and can be interpreted correctly by observers. This distribution reduces the risk of confusion regarding the vessel’s status and intentions at night or in poor visibility conditions.

In a vertical arrangement, evenly spaced lights enhance the visibility of the complete configuration, making it clear that they are part of a signaling system rather than appearing as a single merged light. Equal spacing supports both compliance with regulatory requirements and operational safety by providing a more pronounced visual cue to other vessels.

In contrast, if the lights were spaced too closely or unevenly, it could lead to misinterpretation, where another vessel might not recognize the signaling correctly. This could compromise navigational safety and lead to misunderstandings in the maritime environment.