A 30-meter tug that is underway at night must show sidelights and which additional light?

A tugboat that is 30 meters in length is classified as a vessel that must comply with the navigation rules outlined in the International Regulations for Preventing Collisions at Sea (COLREGs). At night, such vessels are required to display specific lighting to ensure they are visible to other vessels and to indicate their presence and status.

For a tug under way, the requirement is to show sidelights, which are red and green lights indicating the port and starboard sides of the vessel, respectively. In addition to these sidelights, the tug must also display one masthead light and a stern light. The masthead light is white and provides visibility to indicate that the tug is under way. The stern light, also white, is positioned at the rear of the vessel.

This combination of a masthead light, a stern light, and the sidelights is essential for ensuring other vessels can see the tug's outline and determine its direction. In this case, the presence of one masthead light and a stern light, along with the sidelights, aligns with the navigation standards for a vessel of this size and operational status.