Genesis 9: 20 - 25: And Noah began to be an husbandman, and he planted a vineyard: And he drank of the wine, and was drunken; and he was uncovered within his tent. And Ham, the father of Canaan, saw the nakedness of his father, and told his two brethren without. And Shem and Japheth took a garment, and laid it upon both their shoulders, and went backward, and covered the nakedness of their father; and their faces were backward, and they saw not their father's nakedness. And Noah awoke from his wine, and knew what his younger son had done unto him. And he said, Cursed be Canaan; a servant of servants shall he be unto his brethren.
To have a sexual relationship with one’s mother or stepmother was the equivalent of uncovering the nakedness of one’s father; Leviticus 20: 11: And the man that lieth with his father's wife hath uncovered his father's nakedness: both of them shall surely be put to death; their blood shall be upon them.
Ham had a relationship with his stepmother; she was Noah’s second wife and was of the lineage of the Serpent; it was through this woman that the seed of the Serpent came into the new world after the Flood.
Noah awoke from his drunkenness when he was sober and realized what Ham had done; Noah then named and cursed the as of yet unborn seed (Canaan); Noah could not curse Ham because a blessing had already been pronounced upon Noah’s three sons.
The first sin was Eve’s adultery with the Serpent. The first sin in the new world was Ham’s adultery with Noah’s wife. Ham was a type of the Serpent after the Flood.