[Amendment10]

"I think the wood would be all rotted away by now....................."

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Genesis 6:14 shows that G-d instructed Noah to seal (my word) both inside and outside surfaces of ark, hinting divine purpose to at least slow decay imo.

[rdl6989]

This talks a little about how the spaces between wooden planks on ships were caulked to keep the water out.

https://en.wikipedia.org/wiki/Caulk#Wooden_shipbuilding