How the Napier Deltic engine fixed a serious problem for the navy's fast patrol boats

This 1:4-sized model of the Napier Deltic engine was transferred to the Institution of Mechanical Engineers as part of the archive collections of D Napier and Son.

The Deltic engine was developed to meet the need identified by the Admiralty for a high-powered, lightweight diesel engine for fast patrol boats. The Second World War had demonstrated vulnerabilities in using petrol engines, most notably flammability.

The Deltic is a two-stroke opposed-piston compression ignition diesel engine with either three or six banks of three cylinders arranged in a triangle. Crankshafts are located at each corner of the triangle with each crank having an exhaust and inlet connecting rod from the two adjacent cylinders. The crankshafts were connected by phasing gears to a single output shaft.

The first engine was produced in 1950. The Deltic went on to power many of the Royal Navy’s small and fast craft and was still in use in Hunt-class vessels in 2018. The Deltic was primarily used at sea, but it was also used in some British Rail locomotives.

The model is available to view in the IMechE's Virtual Archive: https://archives.imeche.org/archive/artefacts/napier-deltic-engine-0?