Steam boilers

Scotch hybrid boilers

Prud'Hon Capus and Howden-Johnson tried to improve the poor water circulation in the common Scotch fire-tube boilers by adding water tubes in a dry-back combustion chamber.
It was claimed that this modification made them 10 per cent more efficient than conventional Scotch fire-tube marine boilers.
Both types of boilers failed to make an impact despite of these advantages, the disadvantages of the hybrid arrangement being greater than the advantages.

Prud'Hon Capus marine steam boiler

Thirty-two "Prud'Hon Capus" boilers were fitted onboard the cruise liner "Ile de France" in 1927. The operation pressure was 16 bar

The red coil, to the right of the
convection water-tubes, is the superheater.

A Prud'Hon Capus marine steam boiler with the common dry-back combustion chamber open for service.
Two fire-tubes and some of the convection water-tubes are visible on this picture.

Howden-Johnson marine steam boiler

Three Howden-Johnson marine boilers were installed onboar T.S. Crispin in 1935.
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 superheater.

The Howden-Johnson marine steam boiler without the common dry-back combustion chamber mounted.
Part of the superheater is visible above the convection water-tubes