Fishing trawler.
Actually have been present during a rogue wave hitting from astern and washing every item on deck to the superstructure. Viewed the activity from an aux. maneuvering station on the bridge level, during a materials transfer. A solo wave at least three times the average height preceded by an equally deep trough, dropped the stern sufficiently for the wave to top the fencing and ride the deck forward.
An interruption of the evolution had just occurred, and no crew were present in that area, so casualties were avoided. In this type of incident, there are no tattle tale signs before, or remnant changes afterward in the sea conditions. Rogue waves just happen, seemingly at random.