coracle vs rowboat

coracle

noun
  • A small circular or oblong boat made of wickerwork and made watertight with hides or pitch, propelled and steered with a single paddle and light enough to be carried on a person's back. 

rowboat

noun
  • A small open boat propelled by oars (by rowing). 

verb
  • To row a boat of this kind. 

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