What are the requirements for the horizontal positioning of masthead lights on a vessel of greater than 50m in length?

The requirement that masthead lights on vessels greater than 50 meters in length must be positioned one above the other, with specific separation, is grounded in the need for proper visibility and identification at sea. According to the International Regulations for Preventing Collisions at Sea (COLREGs), these lights are critical for indicating the presence of the vessel to other vessels and ensuring safe navigation, especially in conditions where visibility is poor.

By positioning the masthead lights vertically with a specified distance between them, the lights create a clear and identifiable signal that distinguishes the vessel's size and navigation status. This arrangement helps other mariners to determine the range and bearing of the vessel from different distances and angles, which contributes to collision avoidance.

The other factors mentioned in the incorrect options, such as equal heights or symmetrical spacing, do not address the specific requirements for vertical positioning and separation set forth in the COLREGs. Similarly, while visibility from all angles is important, this option does not capture the requirement for specific vertical positioning of masthead lights, which is essential for them to serve their navigational purpose effectively.