Britain’s last major engine designs

A fundamental design fault with the Ruston AO and the commercial failing of the Doxford Seahorse marked the end of an era.

By the late 1960s, the building of large marine engines in the UK involved licensed construction of foreign designs (primarily those of Sulzer and Burmeister and Wain) other than Doxford’s opposed piston units. Medium speed engines were better placed with a number of designs including those from Ruston. It was at this time the two latter companies launched designs which, it was hoped, would revive Britain’s future in the sector. Sadly, this was not to be.

The sad tale of AO

The Ruston AO was developed as a medium speed engine which would combine excellent power potential with light weight. It was a revolutionary design in that its structure comprised a ‘space frame’ of girders forming a lattice work in which liners, crankshaft and cams were supported, rather than the cast frame of traditional designs. The turbocharged and intercooled engine was introduced in 1968 and was available with 6, 8 or 9 cylinders in-line and in 12 and 16 cylinder vee-form units producing from 3,000 to 8,850 horsepower. 

There was much interest in the potential for the design and orders were received from Reardon Smith, British Rail for a ferry, Scottish Ship Management (SSM) for a series of six bulk carriers to be built in Norway, and three of a new class of five smaller fleet tankers for the Royal Fleet Auxiliary (RFA).  

Unfortunately, there was an inherent problem with the basic concept – with the engine turning over at 500 rpm and producing combustion on every stroke, the heat build-up was too much for the lube oil to manage and its consumption became excessive; there were other problems too which only manifested themselves once the engines went into service. 

The first engines to be produced were four 9 cylinder versions for the 7,359 gross ton British Rail ferry St. George, however the first engines to go into service, in July 1968, were two 9 cylinder in-line engines installed in Sir William Reardon Smith's Welsh City. The St George installation of four AOs totalled 18,000 horsepower and the vessel was used for the overnight ferry service between Harwich and the Hook of Holland. Operating at less than full speed to arrive in Holland at a reasonable hour in the morning, the vessel only needed to operate on three of the engines. This was a blessing as, apparently, she never had all four engines in a fit state to operate at the same time!

The RFA tanker Blue Rover which was one of three vessels initially powered by Ruston AO engines (Ships and the sea)

Re-engining

Particularly galling must have been the happenings at SSM. The six Haugesund-built bulkers were each equipped with a pair of AOs driving a single screw through a twin input/single output reduction gearbox. With excessive lube oil consumption, despite Ruston agreeing to pay for all lube oil consumption above an agreed rate, SSM’s management finally gave up the battle and decided to re-engine the vessels. This, of itself, was a major exercise with each ship having to be drydocked and a hole cut in the side for the removal of the existing engines and the installation of their replacements. SSM, on the advice of its marine superintendent, chose to fit the new, medium speed, four stroke Stork Werkspoor TM410. Alas, this engine too was suffering teething troubles, in particular cracked bedplates (a problem solved a little later with a slightly modified design). The SSM ships suffered this second setback and as a result the superintendent lost his job – such are the risks of being a marine superintendent. 

The three RFA Rover class tankers also suffered problems with vibration and were re-engined with Pielstick medium speed engines in 1974 – the other two vessels in the class were built with Pielsticks. Even the Welsh City had to be re-engined, again with Pielsticks.

Doxford's last foray

The swansong for the Doxford brand was the company’s attempt to enter the medium speed market with its Seahorse design. This was a 580 mm bore, four cylinder medium speed engine developed as a joint venture with Hawthorn Leslie, a major Doxford licensee, but only the prototype was ever built. Output was 2,500 horsepower per cylinder at 300 rpm and it would have been available with 4 to 7 cylinders. A wooden mock-up of the engine was exhibited at a marine exhibition in London in 1972 and was inevitably nicknamed the ‘wooden horse’.

The final demise

Sadly, no sales materialised for the Doxford design, and the company finally closed in 1980, ending 66 years as a marine diesel engine builder. 

For Ruston there was something of a retrieve as it was able to continue building its smaller, medium speed engines for a few years more but was finally taken over by MAN in 2000 when the German company bought Alstom Engines Ltd. of the UK with its brands Ruston, Paxman and Mirrlees Blackstone.

John Barnes is a journalist and author and former editor of Marine Engineers Review. 

Editor's Update 

The above reference to the Doxford Seahorse, implied it was the last engine to be built by the company – it was instead its last totally new design though some of its features were adopted by the later 58JS, a short stroke version of Percy Jackson’s J type that had been introduced in 1962 and remained in production until 1980.