You're assigning some notion that berthed means berthed in a home port. Ships are berthed in many different places and times. So the "time which berthed them" just doesn't work.
It does. They were tied to a point in time. They are destined not to be. It’s really very simple. I’m sorry you can’t understand it.
Mixing metaphors and claiming a now-unmoored vessel is more likely to be contrasted with one in a state of being “born” than “berthed” is what “doesn’t work”.
Especially considering “unmoored” is a nearly exact antonym of “berthed”, whereas a ship is never described as being “born”. Christened, perhaps. But certainly not born.
It's an action though, "the time that XXX'ed them". Birthed fits there well, berthed does not. Had it said "the time they were berthed to" I would understand your point better.
Perhaps you're right and it was remembered or quoted wrong, and the word really is "berthed", but it wouldn't have been just the one word remembered incorrectly.
There is no categorical semantic difference between "berthed" and "birthed". They are both past participle tense verbs and fit equally well with no changes needed to the rest of the sentence. Perhaps you simply have more experience hearing birthed in that context and perceive it to fit better? But in reality they really are grammatically identical.
