load line vs plimsoll

load line

noun
  • The line on the outside of a vessel indicating the depth to which it sinks in the water when loaded. 

plimsoll

noun
  • A rubber-soled lace-up canvas shoe for sports or onboard ships; a precursor of trainers. 

  • The plimsoll symbol ⦵ (or o) that is used as a superscript in the notation of thermodynamics to indicate an arbitrarily chosen non-zero reference point. 

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