The armored warships used by the Koreans against Japan a few centuries back were not all that large. Indeed, there is a full-scale model of one in a Korean military museum.
The maximum length of any wooden ship is 90 meters; larger hulls cannot handle the wave stresses. It has nothing to do with "moving under sail." The Ark and those mythological Chinese junks are simply physically impossible. The Chinese may have been making steel in the Middle Ages, but until the 19th century it was impossible to make steel in the quantites required for building large, iron-framed ships -- which is one reason they were not built until the 19th century.
The thing I was referring to early was not turtle ships or ships at all for that matter, but floating forts which were used in an earlier war, in the first millenium AD. Those were much larger than any known wooden ship with the possible exception of Zheng He's largest ships.