Five persons armed with knives and a pipe wrench boarded the tanker and tied up the aft watch keeper.
They subsequently broke into the ship’s paint store, the IMB said.
Once the alarm was raised and crew mustered, the robbers escaped with some of the ship’s stores.
This is the second robber attack on a tanker to take place at the same anchorage within seven days.
The first occured on 21st March when three robbers boarded a crude oil tanker.
They threatened a crew member with a knife and stole his radio before escaping.