Thanks all.
For the reference, I had rescued crews before, after reading the PDF you mention, in much rougher seas than what I have now.
So I know I have to be all stop, close etc.. but didn't make it obvious in my previous comment.
The problem is that even with that (and when I run over that lifeboat, I wasn't moving, the liferaft was), I can't get the red cross.
Now that I think about it, I don't believe I ever got the message about life raft spotted - I got ship spotted (there was an IJN destroyer nearby), but nothing specific about the liferaft.
That could well be it, that the game didn't register it. The blue mark on the map is way away from the orange smoke as well. I'll try to run around a bit, and see before giving up.
@KaleunMarco - thanks!, mapping will help (once the game recognises them as survivors..)
edit: @PB re port side approach - you can move with arrow keys around the boat, so it doesn't matter where you are
. I didn't test whether when on the hull it moves less (it should) than on the conning tower though.