buoy vs freeboard

buoy

noun
  • A float moored in water to mark a location, warn of danger, indicate a navigational channel or for other purposes 

  • A life-buoy; a life preserver. 

verb
  • To maintain or enhance enthusiasm or confidence; to lift the spirits of. 

  • To support or maintain at a high level. 

  • To keep afloat or aloft; used with up. 

  • To mark with a buoy. 

freeboard

noun
  • The vertical distance between the waterline and the uppermost watertight deck of a vessel. 

  • The distance between a water level and the top of something that contains or restrains it (such as a dam). 

  • The distance between the top of sea ice and the water level. 

  • A type of skateboard which simulates the movement of a snowboard when used on a downhill coarse, allowing snowboarding techniques, which has an addition of two centerline casters that extend below the traditional skateboard wheels and bogies. 

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