What does yellow over yellow indicate when displayed on a vessel?

The display of yellow over yellow signals that a vessel is pushing ahead on a tow. This configuration is part of the International Regulations for Preventing Collisions at Sea (COLREGs), specifically related to the navigation lights and day shapes that vessels are required to display based on their status and activities.

In maritime communication, colors and shapes have specific meanings to ensure safety and clarity on the water. Yellow indicates a towing situation, and the combination of two yellow lights or shapes signifies that the vessel is engaged in pushing a tow, which is a common occurrence with tugboats or other vessels that are maneuvering large objects.

Understanding these signals is crucial for safe navigation and avoiding collisions, as this informs other vessels of the presence and activities of the vessel displaying the lights. Therefore, recognizing yellow over yellow as an indication of a vessel pushing another is key for mariners to maintain safe distances and take appropriate actions in response to these signals.