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What on earth was Dean thinking of?

Discussion in 'Steam Traction' started by LesterBrown, Mar 25, 2020 at 9:37 PM.

  1. LesterBrown

    LesterBrown Member

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    In an attempt to get the GWR off the current Webb thread I thought I would ask this question about the infamous 3521 class.

    Dean did have a few other disastrous designs such as no 9 and the tandem compounds but they are quite excusable as individual experiments to you out novel ideas. But just looking at one of his 3521s it is hard not to come to the conclusion they will ride badly. I just cannot understand why he produced them. There was a need to replace the old Bogie (Corsair) type 4-4-0STs down in the South West with new convertibles, but he had two years earlier turned out a ten of the double frame 3501 class 2-4-0T which achieved that aim. Ten similar standard gauge locos were built at the same time, initially fitted with condensers for the Severn Tunnel they soon moved onto short main line services such as London to Oxford and Trowbridge to Weymouth.

    But then in 1887 he turned out twenty of the unusual sandwich frame 0-4-2Ts with a close together pair of coupled axles at the front end and a trailing axle at the other end held in place only by the spring suspension links. They did have a longer firebox and a very high, for the time, boiler pressure of 180lb. Even while the class was under construction they were found to be unsteady and the tanks were reduced in size to now hold less water than the earlier 2-4-0Ts and after a while the boiler pressure had to be reduced.

    But then, with more passenger convertibles needed on the broad gauge he ordered twenty more of the things, shortening the firebox to reduce the wheelbase to the trailing axle, so their boilers were now the same length as the 3501s.

    They were still unsteady so the last one was turned out with a suspension bogie, which helped a little.

    But I just can't work out why he kept turning the ridiculous things out, especially when he could easily just have turned out more of the 2-4-0Ts, perhaps with a high pressure boiler.

    Sir Daniel Gooch was still alive, and the company chairman, when the first batch were produced for the narrow gauge; I wonder what he made of them?
     
  2. Jimc

    Jimc Part of the furniture

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    I don't think I've ever seen any speculation about the design that seemed to me to have much value. When you look at them the most striking feature seems to me the firebox and ashpan right out in open air, rather than behind wheels. That's a theme also visible in presumably related types like the 0-4-4s 34 & 35 and those strange 0-4-4 conversions of ex Monmouthshire railway 0-6-0ST. That seems to me the most obvious difference from Armstrong types, plus also a long wheelbase. But what the design aims were I couldn't guess. Holcroft has nothing much to say about them other than the riding qualities.
     
  3. LesterBrown

    LesterBrown Member

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