pier vs slipway

pier

noun
  • A raised platform built from the shore out over water, supported on piles; used to secure, or provide access to shipping; a jetty. 

  • A structure supporting the junction between two spans of a bridge. 

  • A similar structure, especially at a seaside resort, used to provide entertainment. 

  • A rectangular pillar, or similar structure, that supports an arch, wall or roof, or the hinges of a gate. 

slipway

noun
  • A sloping surface, leading down to the shore or to a river, on which ships are built, repaired or stored and from which they are launched. 

  • A slip road. 

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