freeboard vs seawall

freeboard

noun
  • 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. 

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

seawall

noun
  • A coastal defence in the form of a wall or an embankment. 

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