boater vs riverboatman

boater

noun
  • Someone who travels by boat. 

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

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

riverboatman

noun
  • Someone who pilots a riverboat 

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