What does it mean if a vessel displays red and green lights but no white light?

When a vessel displays red and green lights but lacks a white light, it indicates that the vessel is classified as a sailing vessel operating under sail. In this case, the red light represents the port (left) side of the vessel, and the green light represents the starboard (right) side.

According to navigation rules, when you're approaching a sailing vessel head-on, whether it is using its sails or has additional propulsion means, you must give way to it. This is because sailing vessels under sail have the right of way over power-driven vessels when it comes to these situations on the water.

The understanding of light configurations is essential for safe navigation, as they help to identify the type of vessel and its activity, ensuring that mariners can make informed decisions to avoid collisions and promote safe passage.