first mate vs swabber

first mate

noun
  • An officer on a merchant ship next in rank to the captain and responsible to the captain for the safety and security of the ship. 

swabber

noun
  • An interior officer on British warships, responsible for seeing that the ship was kept clean. 

  • An instrument for swabbing. 

  • A baker's implement for cleaning ovens. 

  • One who swabs a floor or deck. 

  • Four privileged cards, formerly used in betting in whist. 

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