Under the
Whyte notation for the classification of
steam locomotives by
wheel arrangement, the 4-6-0+0-6-4 is a
Garratt locomotive. The wheel arrangement is effectively two
4-6-0 ten-wheeler locomotives operating back to back, with the
boiler and
cab suspended between the two swivelling power units. Each power unit has two pairs of
leading wheels in a leading bogie, followed by three coupled pairs of
driving wheels and no trailing wheels.
A similar wheel arrangement exists for simple
articulated locomotives, but is referred to as 4-6-6-4. On a simple articulated locomotive, only the front engine unit swivels while the rear unit is rigid in relation to the main frame.
Overview
This was a rare wheel arrangement for Garratt locomotives, with only seven locomotives built for two South American customers.
The first was for the metre-gauge Mogyana Railway of Brazil, with five examples built by
Beyer, Peacock and Company in 1912 and 1914.[1]
The other was two locomotives built for the 3-foot gauge Ferrocarril Pacifico de Colombia by
Armstrong Whitworth in 1924.[2]
4-6-0+0-6-4 Garratt production list – All manufacturers[1][2]