Trying to find short story about post-disaster survivors coming ashore from boats in ocean to find everybody dead from (if I remember) inter-generational mass slaughter. Think they find apartment with corpses of adults versus teenagers. They return to ships (rafts?) Thanks.
This is "Shark Ship" by Cyril Kornbluth. The land has been taken over by a death-obsessed cult, the protagonists live on ships that harvest plankton and (almost) never touch land.
By the time of the story, the land dwellers have (mostly) wiped themselves out (the intergenerational murder you mention is definitely a factor). The protagonists' ship loses its net and they face starvation if they don't return to the land.