There are two types of this launch, a  standard version and this lighter version. The information sheet for the drawings below state:

“This design was developed in 1935 to replace the existing 45ft Motor Launch,; the new design to be a lighter craft to be carried in reconstructed capital ships and to be within the lifting capacity of the aircraft cranes.”

John Roberts states that “42ft motor launch was similar but had only a single rubber, like the 42ft sailing launch from which it was derived. The rubber or rubbing strake is the line at the outside of the hull running the entire length, either a timber of rope. I use Robert’s information to classify all large launches as either 42 or 45 ft.