Dont worry... depending on your location a lot of those survivors will have frozen to death before first light.
when it comes to real life:
Disperse some water and one or two large dry blankets if available and sail on.
You might even ask them if they managed to get off a distress signal... if not, ask the name of their ship and send a distress signal for them on open frequency. make no mention of any U-boat. of course.
the best thing that can happen is another nearby ship will reach them within a couple of hours, or perhaps a flying boat will come along and land to claim them.
worst case scenario.... sailor-cicles
