What type of vessel is indicated by showing two cones with their apexes together?

The indicator of two cones with their apexes together is used to signify a specific type of fishing activity, namely trawling. When a vessel is engaged in trawling, it typically has fishing gear deployed to catch fish from the water column, and the visual representation of the cones symbolizes the nets being towed. This configuration helps other vessels recognize that they should exercise caution in the vicinity, as the trawling gear may extend out behind or to the sides of the vessel, creating potential hazards.

The other options represent activities that have different signaling conventions. For instance, a vessel engaged in dredging would be indicated by different shapes, such as a cone with its apex pointing downward, to indicate the passage of dredging equipment. A research vessel might have distinctive markings related to its studies, while a vessel under sail would typically represent its sail configuration, usually shown with a triangular sail shape. Each of these vessel types has unique visual signals to help maintain safe navigation and awareness on the water, but the specific conjunction of cones with their apexes together is unique to trawling operations.