What should a vessel do if it sees another vessel displaying the same sidelights but with no sternlight?

If a vessel sees another vessel displaying the same sidelights but no sternlight, it indicates that the other vessel may be a sailing vessel that is either at anchor or a vessel that is not properly exhibiting all of its required navigation lights. In this situation, the navigating vessel must take extra caution and plan to give way immediately.

According to the International Regulations for Preventing Collisions at Sea (COLREGs), all vessels must display specific lights to signify their type and activity. A vessel that lacks a sternlight but shows sidelights may not be in compliance with navigational lighting rules, which could lead to confusion about its status. Thus, as a precautionary measure, the navigating vessel should be prepared to alter course or speed, allowing for a safe passage and to avoid a potential collision.

This emphasis on safety and the requirement to give way is particularly pertinent when navigation is being conducted in a congested waterway or at night, where visibility is compromised. The rules for lighting are designed to help all vessels understand one another's intentions and activities on the water, so recognizing unusual lighting arrangements is a crucial part of safe boating.