boater vs copilot

boater

noun
  • One who works on a boat, especially as captain. 

  • Someone who travels by boat. 

  • A straw hat, very stiff, with a flat brim and crown. 

copilot

noun
  • A backup or assistant pilot of an aircraft. 

verb
  • To serve as relief or assistant pilot. 

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