tonnage vs vessels

tonnage

noun
  • The number of tons of water that a floating ship displaces. 

  • The capacity of a ship's hold etc in units of 100 cubic feet. 

  • A charge made on each ton of cargo when landed etc. 

  • The number of tons of bombs dropped in a particular region over a particular period of time. 

  • The total shipping of a fleet or nation. 

vessels

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