Noah was a good enough engineer, whether he got the plans from God or dreamed them up himself under the inspiration of God, to correctly execute these very ambitious plans. The plans are spelled out in detail. The ark is to have three levels. It is to be caulked both inside and outside. It is to be three hundred cubits long, fifty cubits wide and thirty cubits high. The dimensions of the ark are given so distinctly that they serve the literary purpose, of course, of concretizing the description and so make it as if it happened. But this is an interesting set of descriptors. “Genesis” could have said large or very large or as tall as a cedar of Lebanon or some other metaphor for size. “Genesis” does tend to exaggerate when it gives particular numbers, as when it gives the ages of the generations between Adam and Noah. That makes the story legendary: an exaggeration of what might have happened in the past rather than treating the past as having a very different set of processes than does the present, which is what happens when a mythology is created. There seems to be a different reason for concretizing here in the Noah story.