BUCHAREST—After 40 years at sea, on his final voyage earlier than retirement, Captain Dan Sandu slipped into his cabin on the MV Vantage Wave, a cargo ship crusing away from India, feeling unwell. “Don’t fear,” he typed in what could be a last electronic mail to his spouse in April. “Every little thing shall be effective.”

Final month, the ship, by then floating off the United Arab Emirates, despatched what had turn into a well-known plea. Captain Sandu was lifeless and his physique was within the ship’s walk-in freezer. For six months, it had traveled 1000’s of miles mendacity close to the crew’s meat and greens. They wanted to get him again to Romania.