Double-ended boilers.
Figs. 37 and 38 show a double- ended boiler. This is a common type for
mercantile steamers, and is also fitted in a considerable number of ships of
the Royal Navy. It is practically equivalent to two single-ended boilers placed
back to back, but lighter for equal power, because the weight of the end plates
and of much water in the spaces at the backs of the combustion chambers, is
saved. ..........
Marine locomotive boilers.
Figs. 44 and 45 illustrate the locomotive type of boiler which has been used
for marine purposes in torpedo boats, etc., in which the working pressures of
steam have been from 120 lbs. to 180 lbs. per square inch. In this type of
boiler there is a broad and practically rectangular fire-box at one end, the crown
of which is strengthened by means of stays to the roof of the boiler, as
shown. The example illustrated is by Yarrow & Co.
The air for
the combustion of the coal is supplied from underneath, and there is
considerable space and height above the fires to allow for the combustion of
the gases. The barrel of the boiler beyond the furnace is cylindrical, and
contains the tubes which lead to a smoke- box at the opposite end of the
boiler. ..........
In both torpedo boats and torpedo gunboats, however, the locomotive boiler has
now been abandoned in favour of the water-tube boiler described in the next
chapter.