"They can't do any online banking. They can't pay their bills at home. They don't have any of their data or anyone's contact information, so they're really isolated right now," Mr Messick said. "They just can't reach out to the folks they need to, or even look at pictures of their children before they go to sleep. It's really a sad situation."

The plight of the sailors also attracted the attention of the two unions representing them, the Singapore Maritime Officers' Union and the Singapore Organisation of Seamen.

In a joint statement on 11 May, the unions said that "morale has understandably dipped", driven by "unfounded fear of personal criminal liability" and emotional distress.

The statement also called for the "swift return" of the crews' phones, noting that losing communication with family members is "causing significant hardship for crew members with young children at home."

Dave Heindel, the president of the Seafarers International Union, said that "however long the investigation takes, the crew's rights and welfare should not be infringed upon".

"We call on the authorities to be mindful that seafarers utilise mobile devices to conduct personal business for bill payments, and, more important, transfer money to their home country to sustain families," he said. "Crew members are becoming demoralised without the basic tools we all take for granted."

Andrew Middleton, who runs Apostleship of Sea - a programme that ministers to ships coming through Baltimore - told the BBC he visited the sailors two weeks ago and found them in "good spirits" despite constant worries.

"Once we broke the ice and got everyone to say their name and what part of India they were from, and talk about if they were married or had children, we got the ball rolling," he said. "They were willing to kind of poke fun at one another a little bit.... we did our best to get them laughing and joking, hopefully to take their mind off things for even a few minutes."