life raft vs steamboat

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. 

steamboat

noun
  • A boat or vessel propelled by steam power. 

  • Hot pot (Chinese dish). 

verb
  • To travel by steamboat. 

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