What made four decks the limit for an age-of-sail ship?
Short answerThey were not absolute limits; development moved to newer ship concepts before navies had enough reason to build still larger wooden ships.
NotesFour decks did not form an absolute technical maximum for a sailing warship. Larger ships could have been developed with enough time and a reason to build them. Naval development moved on to other concepts before shipbuilders pursued that course. The largest designs discussed here therefore mark how far development went, without proving that further growth was impossible.