In the case of a trireme, we have some records of voyages over known distances that allow us to calculate their speed and the we also have some reconstructions. Korean naval voyages were likely all short distances, and so oars may have been used, which could have raised the speed. For short distances, triremes were capable of over 7 knots, as
Xenophon widely quoted reference to a single day's voyage from Byzantium to Heraclea Pontica, shows. . https://en.wikipedia.org/wiki/Trireme
Here is a list of ancient sailing speeds for the Mediterranean. Note a sailing speed of 4 - 5 knots was typical speed under favorable winds, For short 1 day voyages, up to 8 knots could be achieved with warships. .
http://penelope.uchicago.edu/Thayer/...nt_Ships*.html
For a replica 17th century galleon, the average speed was 7 knots.
http://tallshipsportland.org/el-galeon/. However this speed was appears to be for good weather, being a replica it had not need to sail under bad weather. When looking at actual voyages of 18 century to early 18th century sailing ships on long voyages, the actual speed would be less.
https://www.econstor.eu/bitstream/10.../786607629.pdf
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