This extraordinary looking hat has a firm historical basis and was particularly favoured by sailors between the sixteenth and eighteenth centuries. The shaggy thrum surface makes it exceptionally warm, and able to repel a lot of weather. Today, yes, it does look just a little bit like a cuddly pet monster, but we won't hold that against it!
Like all my range of historic patterns, this comes with supporting references and notes to place these hats in context.
Yardage will vary a bit depending on how heavily you thrum your cap, best to use a yarn you have plenty of for this part, just to be on the safe side.