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The NapierLion engine had been fitted in boats for racing and World record attempts.  In 1928 four Napier Lion VII engines were fitted in the 78' Saunders craft "Jack Stripes" for a Trans-Atlantic Crossing attempt.  Then Betty Carstairs fitted one in her Saunder Hydroplanes Estelle I and II.  This use of Lion engines in marine craft continued so, in 1929, the Company developed the Lion XIA engine to design E92.  This 560 hp engine was the basis for the 'marinised' 500 bhp Napier SeaLion engine.

'W' Water-Cooled Marinised Engine

Design E92   1932  

12-cylinder 5.5" bore x 5.125" stroke

24 litre

Where to see:

    Lorne Jacobs forthcoming Railton style vehicle

    Museum of Flight, USA    

    National Museum of Flight, East Fortune, Scotland

    RAF Hendon Museum, London

Napier SeaLion engine
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In the early 1920's Hubert Scott-Paine owned the Supermarine Company which, of course was involved in the Schneider Trophy.  After selling Supermarine in 1923 he became a director of Imperial Airways until 1939.  In 1927 Scott-Paine formed the  British Power Boat Company and adopted the SeaLion engine and entered into an agreement with DNS for them to produce the 'Power-Napier SeaLion' giving the ageing engine design a new lease of life.


By 1938 more than 200 SeaLions had been fitted by the British Power Boat Company in Hythe.  Over the following 20 years a further 2,000 were required, plus spares, for the Army, Navy and Air Force.  They used Britsih power Boat High Speed Launches (HSL). Fast Patrol Boats (FPB) and Motor Torpedo Boats (MTB).

During WWII Tank Landing Craft were also fitted with two SeaLions.  In 1956 Vosper built a new Air-Sea Rescue Target Towing Launch (RTTL Mk1A) with three SeaLions while awaiting a Rolls-Royce alternative.  This was the final Lion / SeaLion engine application spanning a forty year period only being exceed by the Napier Deltic for longevity.


At this time all British small boats were powered by petrol fueled engines.  Events like the destruction of 12 MTBs and loss of 64 lives as a result of an accidental fire in Ostend harbour in 1945 drew attention to the inherent risk of petrol powered wooden boats.  In 1943 Sir Roy Fedden (ex. Bristol Engine Company) chaired an investigation into a new diesel engine for future designs of FPB / MTB namely the RN Dark Class.  The new marine engine design eventually proposed and selected was to become the Napier Deltic.


During WWII the Admiralty also investigated the use of Napier Sabre engines in MTBs.  The 'SeaSabre' engine project of 1942 utlised the basic Sabre V derated to 2,000 bhp at 3,500 rpm and had a marine gearbox with integral clutch and reverse gear.  A large 45-knot, long duration, sea-going air-sea rescue launch, needed four 'SeaSabres' giving 8,000 bhp combined output  After the prototype had been tried and tested in the Solent it was cancelled with the work passing on the the US Navy.