hogback vs whaleback

hogback

noun
  • A Viking grave marker taking the form of a recumbent monument, generally with a curved (hogbacked) ridge and outwardly curved sides. 

  • A sharp steep-sided ridge formed by the erosion of tilting strata 

  • A hogframe. 

whaleback

noun
  • A landform (typically a sand dune) having the form of the back of a whale. 

  • A kind of cargo steamship with a hull that continuously curves above the waterline from vertical to horizontal. 

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