CMB Replica - Costal Motor Boat

The CMB Replica boat is intended to be a fully operational reproduction of a 40ft CMB. The boat is being built entirely by volunteers, guided by experienced boatbuilding professionals. Although the build is using modern glues, all the techniques are traditional ones that would have been deployed in 1916. The boatbuilders are working from the original plans drawn on wax cloth and annotated by the designer John Thornycroft. 

The construction of the boat is a project funded by the Chancellor using LIBOR funds.

The original batch of Coastal Motor Boats (CMB’s) were designed and constructed in 1916 by John I Thornycroft at Platt’s Eyot at Richmond on the River Thames.  The War Department’s specification was for a fast, shallow-draught boat, capable of passing through a minefield and then delivering an 18-inch Whitehead torpedo.

Boats of this type were used in raids on Zeebrugge and Oostende but, most famously, in two raids on the Bolshevik fleet in the port of Kronstadt in June and August 1919.  In the first daring raid, the cruiser “Oleg” was sunk outside Kronstadt Harbour, for which Lieutenant Augustus Agar was awarded the Victoria Cross and promoted to Lieutenant Commander. Seven CMBs took part in the second raid for which two other officers were awarded VCs and Agar was awarded the Distinguished Service Order.

“Coastal Motor Boat” was a “camouflage” term for the boat, so as to not give away its true purpose.

Boat Stats

Length Overall



8ft 6in




4 tons


Cummins QSB 6.7 litre diesel engine


Double skin mahogany

Date Built

Currently under construction

Boat Yard

Boathouse 4, Portsmouth Historic Dockyard


Supported by:

Supported by Regional Growth Fund