There are two types of this launch, a standard version and a 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.”

Drawings of the standard type have not yet been located.

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.

 

A 45 motor launch behind a 50ft Steam Picket of HMS Ramillies, possibly showing the supports of a detachable cabin?

WITH THE ROYAL MARINES ASHORE AND AFLOAT. 1940, ON BOARD HMS RODNEY AND ASHORE. THE VARIOUS TASKS PERFORMED BY THE ROYAL MARINES.
WITH THE ROYAL MARINES ASHORE AND AFLOAT. 1940, ON BOARD HMS RODNEY AND ASHORE. THE VARIOUS TASKS PERFORMED BY THE ROYAL MARINES. © IWM (A 129)

Possibly the standard type barge.

ON BOARD THE BATTLESHIP HMS RODNEY. OCTOBER 1940, SCENES IN THE DAILY ROUTINE OF THE BATTLESHIP. ON BOARD THE BATTLESHIP HMS RODNEY. OCTOBER 1940, SCENES IN THE DAILY ROUTINE OF THE BATTLESHIP. © IWM (A 1425)

Possibly the standard type barge.