Investigators on Tuesday boarded a heavily damaged oil tanker that caught fire in German waters in the Baltic Sea late last week, starting a probe into the cause of the fire. The tanker ship Annika was travelling between the German Baltic Sea ports of Rostock and Travemünde with 640 tonnes of heavy oil when a fire broke out on board on Friday morning. At the time, the ship was about 4.5 kilometres off the coast of the eastern German town of Heiligendamm, a popular Baltic Sea resort. Clouds of smoke could be seen from the beach, and photos showed the entire aft deck in flames. After initial ext…