mainsail vs spanker

mainsail

noun
  • The largest (or only) sail on a sailing vessel. 

spanker

noun
  • A fore-and-aft gaff-rigged sail on the aft-most mast of a square-rigged vessel. 

  • An instrument used to give someone a spanking or spank, such as a paddle. 

  • Someone who spanks. 

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