merchant marine vs pilotage

merchant marine

noun
  • A ship dedicated to commercial, rather than military, purposes. 

  • Synonym of merchant navy. The fleet considered as an entire combined force. 

pilotage

noun
  • The use of landmarks to guide a vessel or aircraft to its destination. 

  • The occupation of a pilot. 

  • The fee paid to a pilot. 

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