clear sailing vs plain sailing

clear sailing

noun

  • A situation where one can proceed with no serious problems. 

plain sailing

noun

  • Something that is simple, straightforward, or easy; something that offers no troubles or difficulties. 

  • The navigation of waters free from hazards or unfavourable winds. 

adj

  • simple, straightforward, or easy 

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