A drawing showing the boiler of the tug "Gnat" produced by Stephens, Smith and Co and dated 21st December 1886. The drawing shows the general arrangement of the boiler and also includes two notes, one stating that the working pressure was 150lbs and another stating that it is tracing number two referred to in a contract between Stephens, Smith and Co and the East and West India Dock company dated 23rd December 1886.