Throughout the Yi Dynasty, treenails were used in almost all of the ship construction, and they were exchanged in a certain period to prolong the life of vessels. Their regulations and effects on the ship construction have been studied. In the 4th King Se-jong era, they adopted the new construction method—double skin Chinese method using steel nails. However in the next King Mun-jong era, they abondoned the complicated Chinese method, and returned to their traditional single skin hull construction with treenails. Since then, Yi Dynasty sticked on the treenail and they were periodically exchanged in the hull constructions. As a result they could prolong the life of vessels. However, Yi Dynasty lost the chance to improve their traditional ship construction.