I found a Youtube video on how to draft a bucket hat by hand: https://www.youtube.com/watch?v=Z-mJs9oMu4A
He starts with the top (crown section) of the hat and uses the ‘Slash and Spread’ method on the sides and brim that are explained in the McCunn method Bell Sleeve tutorial (Bell Sleeve pattern) to create the sides and brim.
I hope this helps 