cockboat vs paddlewheel

cockboat

noun
  • A small rowing boat, especially one pulled behind a larger ship, or used to ferry goods between a ship and the shore. 

paddlewheel

noun
  • A boat propelled by a paddlewheel. 

  • A large wheel fitted with thick slats, turned by an engine and used to propel a boat. 

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