The Floating Graveyard

From the introduction:

When the Old World came to an end, the lands swallowed by gouts of nuclear fire, some tried in vain to escape by sea, only to watch the oceans ripple and boil beneath them. Their vessels became their coffins as busy harbors were crushed by killer tides, tearing mighty ships apart and tossing smaller ships together in a conglomerate of wood, steel, and fiberglass. As time went on, these mass wrecks became the hunting grounds of all manner of mutant creatures, and popular treasure-hunting spots for foolish adventurers.