Scotchman vs Scotsman

Scotchman

noun
  • A piece of wood or stiff hide placed over shrouds and other rigging to prevent chafe by the running gear. 

name
  • A surname. 

Scotsman

noun
  • A man from Scotland; a Scot. 

How often have the words Scotchman and Scotsman occurred in a corpus of books? (source: Google Ngram Viewer )