The Howden-Johnson boiler tried to improve the poor water circulation in the
fire-tube boilers by adding water tubes in a dry-back combustion chamber.
It was claimed that this modification made the Howden-Johnson
boilers 10 per cent more efficient than conventional Scotch fire-tube
marine boilers. The Howden-Johnson boilers as well as the
boiler failed to make an impact despite of these advantages, the
disadvantages of the hybrid arrangement being greater than the advantages.
The operation pressure was 15 bar and the steam was superheated to 307°C.
The red coil, between the convection water-tubes and the smoke tubes, is the
The Howden-Johnson marine steam boiler without the common
combustion chamber mounted.
Part of the superheater is visible above the convection water-tubes