" In short: Miracle! Jehovah kept the boat afloat and the animals alive."
When my son was about 13, he was asked by an MS if he wanted a Bible Study, I did not object, being a very busy guy, and a believing JW at the time. I think the M.S gave up because my son asked so many questions that stumped him, being at that age, 13. In the end, on the Flood Story the MS had to admit that it would be necessary for Jehovah to perform a whole series of miracles to pull it off, my son then asked " But why did he do it at all then? why not something different ?" the M.S gave up "studying" with him shortly after.
My son pointed out to me that the Genesis account seems without doubt to speak of a Global Flood, and that no such thing happened, "out of the mouth of babes" indeed!
We left eventually, my son's comments on the Flood and other matters going in to our minds, and us realising we could not answer him.