Acts 27:20

‘And when neither sun nor stars shone on us for many days, and no small tempest lay on us, all hope that we should be saved was now taken away.'

The blackened sky prevented navigation, and there were no breaks in the clouds. They had no idea where they were. But as the next verses bring out, God knew. Meanwhile the howling winds and the great breakers continued to tear at the ship until all hope of survival was taken away. Not even the most experienced sailor had been through anything like this before.