My dad was a naval architect, so I can answer that one. Drawing was done on translucent paper (tracing paper). If you had to copy another drawing, you could jus

My dad was a naval architect, so I can answer that one. Drawing was done on translucent paper (tracing paper). If you had to copy another drawing, you could just slide it under your current drawing and position a spline to match the line. Once the drawing was done, it was brought to a copy shop that used a special machine to copy it to a paper that turned blue when exposed to light (hence the term blueprint - https://en.m.wikipedia.org/wiki/Blueprint https://en.m.wikipedia.org/wiki/Blueprint). The original drawing on tracing paper was then carefully archived, and more blueprints could be made out of it as needed.