cockboat vs life raft

cockboat

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

life raft

noun
  • A usually inflatable raft carried aboard a ship or airplane, used to save lives in case the vessel has to be abandoned in an emergency on the sea. 

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