Living side by side, Ukrainian and Russian sailors are tested by the war.

Commercial vessels have become some of the few places where Russians and Ukrainians, who make up 15 percent of the world’s 1.9 million sailors, still live side by side on routes around the world while their countries are at war. Some ships have become rare havens of understanding and forgiveness. On other ships, the mood has become tense and at times unbearable, upending the maritime tradition of sailors viewing each other as teammates, no matter their backgrounds.

With the global maritime industry already short of commercial sailors, and especially dependent on sailors from Russia and Ukraine, who tend to be highly skilled, some companies have switched out sailors to cool tension on board.

A.P. Moller-Maersk, one of the world’s largest shipping companies, said in a statement that having Russian and Ukrainians crew members on the same ship could be challenging. “As a precautionary measure, we have decided not to have seafarers from Ukraine and Russia aboard the same vessel,” the company said, adding that this policy had come into effect at the beginning of the invasion in February.

Amid the difficult moments, on some ships, the close contact between Russians and Ukrainians has led to unexpected compassion.

Roman Zelenskyi, 24, a sailor from Odesa, Ukraine, said that after he and the other Ukrainians showed the Russians photos of the damage in the Ukrainian cities of Kharkiv and Mariupol, the four Russians on his ship were shocked and ashamed. “This is people like me working on a vessel,” he said. “We live in peace.”