Those that believe the Ship is the only defined space in all reality claim that flotsam and jetsam take shape and form when approached, modeling themselves off the forms of what is true and separating from the utter unknowable chaos that is the ocean. This may be justified, in that everything seems to keep a theme of being worn down in some way, eaten away by the natural world if such a thing could be said to exist. Beings recovered or encountered seem to have their own internal coherence, however, and other Ships themselves are encountered—dead and empty, granted, but just as if not more put-together than the eponymous Ship itself.
In definition, the two terms define separate classes of objects: Flotsam being larger and Jetsam being smaller.
Ships- Vessels ancient and enigmatic, aimlessly drifting and almost certainly abandoned. Otherwise extremely dangerous if of a functional military construction, or simply by being vast and uncharted. Typified by being very large, from three to six hundred meters in length, and having a tendency towards being made of steel. Seemed to originate as tankers, battleships, aircraft carriers, cargo ships, and large-scale designs, as if no personal vessels survived.
Constructions- Artificial designs that were not explicitly built for seaworthiness that seem to float despite that. Personal houses, temples, skyscrapers, planes, monuments, assembly lines, swathes of plastic and metal shaped into elaborate concentric circles, artificial islands, and the like. Sometimes inhabited by hardscrabble clusters of fishers and foragers, beings who do not know theirs is not the true center of reality.
Landmasses- Rootless and disconnected islands or bits of land that do not at all obey gravity. Bear a variety of biomes and buildings, which may overlap with construction-class Flotsam, and are much more likely to hold some kind of civilization. Entire city-archipelagos, mountains with holes in their sides, swamps growing on superlight hollow crystals, deserts of iron filaments, coastal roads that are entirely coast, and others can be found to exist. Slinks claim to have come from a place of river-deltas made entirely of the crumbled bones of their ancestors.
Environments- Atypical and notable shifts in the ocean's environment itself: when two violet suns emerge from the dawn horizon, when great undersea leviathans swim past in droves and leave vortexes in their wake, when there are leaks in the sea pulling everything down, and such. To their credit, the Crew have never let the Ship sink more than twice.
Cargo- Useful tools and devices either to support or maintain a vessel and its inhabitants, for some reason jettisoned away. Includes firearms, ammunition, metal sheeting, copper wire, intact provisions, clamps, alembics, medicines of any kind, floatation devices, navigation records or report logs, piping, ingots, genetic samples, seeds, surgical implements, and such.
Trove- Secret, usually minuscule or hidden stash of illicit objects. Narcotics, counterfeit money, experimental weaponry, stolen art or intellectual property, neurotoxins, photographs of the Captain, and such.
Salvage- Loose debris and ruins upon the waves. Building facades, rebar clusters, plating and decking, furniture, airplane wings, church bells, still-steaming isotope thermogenerators, personal dinghies, rotten foodstuff, hunting trophies, tea crates, bloated corpses, and such.
Beings- Any being lost upon the waves. If they live to be rescued, that is.