ujm > maximum number of passengers possible given the fact that there are insufficient space
ujm, in practical situation, there are additional factors that will be used:
sort everyone by weight and size (lowest to highest), although one could argue that a fatter person have higher chance of survival (both food and buoyancy)
more important – skills that will help everyone to survive – rowing, doctors, radio amateurs
most important – those whose survival will be important in a longer term – when they land on an island, or even when they come back home. See Teshuva by R Grozdensky in Vilno, 1940 a month before it was occupied. They asked who should get Sugihara visas – older Rabbis who will be first to be arrested and killed, or the younger ones who will lose their children to shmad. He answered older ones – because (1) they’ll be able to help remaining ones better when they come to America, and (2) they are more important for American Jews