page_title: Launch-type boiler
section_title: Conical boilers
hierarchical_section_title: Launch-type boiler / Railway locomotives / Conical boilers
caption_attribution_description: Hohenzollern Locomotive Works Nº447, 600mm heeresfeldbahn locomotive for the Prussian Army, fitted with the Hohenzollern conical boiler.
context_page_description: A launch-type, gunboat or horizontal multitubular boiler is a form of small steam boiler. It consists of a cylindrical horizontal shell with a cylindrical furnace and fire-tubes within this.
  Their name derives from the boiler's popular use at one time for small steam yachts and launches. They have also been used in some early Naval torpedo boat destroyers.
context_section_description: In 1888 the Hohenzollern Locomotive Works delivered the first two narrow gauge 600 mm (1 ft 11 ⁵⁄₈ in) Feldbahn locomotives for the Prussian Army. These used a conical development of the launch boiler. A backplate of enlarged diameter and a greatly reduced smokebox tubeplate were fitted into a steeply conical shell. This was installed with the upper edge of the cone horizontal. The purpose of the conical shape was to increase water depth over the furnace, the hottest part of the evaporative surface. The furnace and tubes were moved to the lower part of the shell, with the tubes running upwards parallel to the lower edge of the cone. A difficulty was the boiler's lack of steam space, requiring an enlarged dome, of almost as much capacity as the main shell. As a major virtue of the launch boiler is the simplicity of its construction, rolling a conical shell and fitting a large dome represented a considerable increase in their complexity and cost.
  These locomotives, and their boilers, were a complete failure. They were undersized and underpowered for the task, with tiny wheels prone to derailment on uneven track and (for the first 2-2-2 locomotive) limited adhesion from its single driver. Despite being some years after Heywood and the publication of his Minimum Gauge Railways, they ignored almost all of Heywood's principles. The boilers lacked evaporative capacity and could not support sustained running.
caption: Hohenzollern Nº 447
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