Russian billionaire Alisher Usmanov was sanctioned by the European Union on Monday. Two days later, Forbes has learned from three sources in the yacht industry that one of his prized possessions—the 512-foot yacht Dilbar, valued at nearly $600 million—has been seized by German authorities in the northern city of Hamburg. The ship has been in the Hamburg shipyards of German shipbuilding firm Blohm+Voss since late October for a refitting job. Sources who spoke to Forbes said that the German government froze the asset and that, likely as a result, Blohm+Voss employees who had been working on the yacht didn’t show...