For this thread, we can compile the largest ships (length) known for each dynastic period based on archaeological finds or from primary accounts. After some time and some generous contributions, CHF may have a nice timeline of Chinese ship sizes. This post will be the master copy that will evolve as forummers provide new information. Only posts with sources, links, or archaeological sites should be considered credible and will be posted.

Tang Dynasty -
Song Dynasty - A ship excavated around Ch'iian-chou harbor was 34.6 meters
Yuan Dynasty - 35 meters
Ming Dynasty -
Qing Dynasty -

So, if you know of some ship sizes, please contribute by listing the Dynasty and/or year, the ship length, and the source.