How strong were turtle ships compared with contemporary European warships?
Short answerThey were likely superior in confined coastal waters, but European sailing warships would gain advantages in open water and long-range mobility.
NotesSpanish galleons would fare badly in the turtle ship's preferred environment. More maneuverable English-style sailing ships complicate the comparison, but the decisive factor is geography: oar-powered Korean vessels excel in littoral waters, while wind-dependent European ships are better suited to open-sea operations. Both sides' cannon were unlikely to defeat the other's strongest protection easily at expected ranges.