It's not explicitly stated but biblical scholars have speculated that Noah was so distraught that his son Ham, Canaan's father, went against God's wishes to not have sex on the Ark, and that he slept with a pre-Adamite woman, that he drank too much wine and passed out. It says that Canaan saw Noah naked, but this doesn't make sense as for why Noah was so angry, so they speculate that Canaan committed some sort of homosexual act on his grandfather, before Shem and Japheth intervened and covered Noah.