snipped: Ok, this gets even more odd. I understand the Vee twin concept and why you would choose that but why have a double acting oscillating with the complication and (I presume) inefficency of that type of valve gear when you could have Vee twin cylinders with conventional valve chests and reversing gear? Slightly more complex in terms of linkage etc but more suitable surely? Roger
Basically because it was cheap and easy to make, is my guess - I have now found the 1988 Steam Boat Association Register. Both engine and boiler were made in 1984 by the Thames Steam Launch Co; the boiler had a heating surface of 35 sq ft (as opposed to 140 sq ft for President's old boiler) and the engine had two 2" x 5" cylinders, a disc crank driving a feed-pump (there was also a hand feed-pump) and was condensing. Reversing was by steam ports like a Mamod. At 55' x 2' draft I would reckon she was underpowered. It's worth saying that many of the 'new' boats in the Register are remarkably crude (the old ones are OK) and I think sensitive and discerning engineers should avoid reading the book. Though the 90 degree V-twin you suggest is a much better design (especially for balance) they're rare, presumably because they require more space and were more expensive to build than a side-by-side engine where the same frame can support both cylinders. The only large-scale application I can recall were the L&L steamers, where presumably the wide hulls gave the space. Gondola has an excellent modern example with helical sleeve reverse. Sean [Non-text portions of this message have been removed]
