hammer beam vs transom

hammer beam

noun
  • A member of a kind of roof truss (a hammer-beam truss), so framed as not to have a tiebeam at the top of the wall. Each principal has two hammer beams, which occupy the situation, and to some extent serve the purpose, of a tiebeam. 

transom

noun
  • Any of several transverse structural members in a ship, especially at the stern; a thwart. 

  • The flat or nearly flat stern of a boat or ship. 

  • The horizontal beam on a cross or gallows. 

  • A crosspiece over a door; a lintel. 

  • Items that have arrived over the transom. 

  • A transom window. 

  • A horizontal dividing bar in a window. 

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