setting pole vs topmast

setting pole

noun
  • A pole, often iron-pointed, used for pushing boats along in shallow water. 

topmast

noun
  • The mast below the topgallant mast in a square-rigged ship. 

  • The highest mast in a fore-and-aft-rigged ship. 

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