The word that is used does not describe a ship but rather a box. The same word is used for the basket in which Moses’ mother put him to save his life (Exodus 2:3). The very big basket
or box
that Noah had to build was also to save lives. He constructed the ark to save his household. That is typical of the covenant of God.
7 By faith Noah, being warned by God concerning events as yet unseen, in reverent fear constructed an ark for the saving of his household. By this he condemned the world and became an heir of the righteousness that comes by faith.