dead calm vs unruffled

dead calm

adj

  • Completely still with no waves and no wind. 

noun

  • The condition of a perfectly flat sea with no waves and no wind. 

unruffled

adj

  • Calm, not ruffled, serene, at peace, unbothered. 

  • Not ruffled or tousled. 

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