life preserver vs water wing

life preserver

noun
  • A buoyant ring or vest intended to keep a person afloat. 

water wing

noun
  • One of a pair of inflatable plastic bands, normally worn on the upper arms, to help a wearer float in water and learn to swim. 

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