system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek] If replication technology exists, shouldn't it therefore be possible for the ships to repair their hulls as long as energy exists to form into matter?
gpt
There's a great debate over whether or not replicators *reconfigure* matter or whether they *create* matter. I've looked at the figures, it makes no sense whatsoever that they *create* matter given the context of how they're treated (in literally dozens of examples) and the figures for power generation, fuel storage etc don't allow for such a system.

When you pee, poop, discard your used dishes or recycle your garments or shoes into a replicator, it breaks it down into a protein/polymer slush. When you replicate your meal, or new shoes, or new clothes, or refresh the air, or replicate a new laptop your replicator takes some of that slush, and applies a carefully-modulated transporter effect, using a synthetic pattern to transform that mass-energy into something else. That's why replicators are slightly limited in quality and diversity, as molecular patterns etc have to be stored on a computer with limited storage space and the replicator occasionally makes booboos and mistakes, and pretty much always introduces compression artifacts into whatever you're making.

As for ship hulls, if the materials can be successfully generated, physical layout quality is adequate and the replicator is big enough, then you can replace hull plates, structural member sections etc and fix them yourself. However this requires an industrial replicator, is relatively slow and puts a significant drain on the ship's resources, with power and replicator mass (which is fairly easy but non-trivial to replace) as well as the extra maintenance etc being problematic. A Galaxy-class ship would have a better setup than a Sabre or Miranda-class for such a task. Also note that landing on a planet, throwing rocks into the replicator, dematerialising them and turning them into self-sealing stembolts probably puts crazy amounts of wear on them, and they'd probably malfunction pretty quickly.

It is also stated that some components are un-replicatable, so even if hull plating could be replaced there would be some things that couldn't be, not without parts and/or a factory.