Sean wrote: snipped: She had a twin-cylinder oscillating engine, like a Mamod on steroids - the cylinders had aluminium cladding and looked like a couple of beer cans, while the boiler casing looked like an airing cupboard.
That's interesting Sean; why would one use an oscillating engine when a double acting one would be more efficient and powerful? ........Unless of course it was an engine that just happened to be available at the time. Roger As I recall Keith Jones' explanation at the 1987 National, the reason for the choice was that reversing was completely reliable as there was no dead centre (I failed to mention that the cylinders were at right angles, driving a common crank-pin so one was at mid-stroke when the other was at dead-centre). I also think the cylinders were double-acting. I think the engine had been made specifically rather than being off-the-shelf - after all, if the hirers were paying the fuel costs, reliability rather than efficiency was the name of the game. The only (and much better-looking) oscillating engine I've seen since was on the Danish paddler Hjeljen which had two double-acting simple cylinders with cranks at right angles and seemed to be completely reliable about reversing at the stops to pick up passengers. That had slide-valves in valve-chests mounted on the (moving) cylinders, operated by (IIRC) Stephenson's Link from the crankshaft. I couldn't get my head round the kinematics of that for more than a minute or two, though it must be obvious to someone who knows what is moving what to operate what - are the cylinders moving their own valves or do the links do it? Rum coves, these Victorians. [Non-text portions of this message have been removed]
