bulwark vs freeboard

bulwark

noun
  • The planking or plating along the sides of a nautical vessel above her gunwale that reduces the likelihood of seas washing over the gunwales and people being washed overboard. 

  • A defensive wall or rampart. 

  • A defense or safeguard. 

  • A breakwater. 

  • Any means of defence or security. 

verb
  • To fortify something with a wall or rampart. 

  • To provide protection of defense for something. 

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 bulwark and freeboard occurred in a corpus of books? (source: Google Ngram Viewer )