[1967 R50/2]

This moral conundrum is just an expansion of a older simpler one:

You and a buddy are the only survivors of a ship wreck. You are both swimming in the middle of the ocean but know you can't keep this up forever. You see a life preserver. It will not support both of you...only one.

If you kill your buddy is it self-defense because you've done what was necessary to save your life? Afterall, if your buddy takes the life preserver, you are dead.

Or is it murder?

With regards to the lifeboat, I will add some complexity. What if it is a prison ship, transferring convicts to some tropical penal colony? Then what? What is the crew's responsibility to thieves, murderers and rapists? The courts have sentenced them to punishment, but not to death.

With a passenger ship, you may indeed have thieves murderers and rapists on board, but not know it.