The Johnson boiler is a

water-tube boiler A high pressure watertube boiler (also spelled water-tube and water tube) is a type of boiler in which water circulates in tubes heated externally by the fire. Fuel is burned inside the furnace, creating hot gas which boils water in the steam-gene ...

used for ship propulsion. The Johnson design was developed by the British engineer J. Johnson in the late 1920s. A patent was granted in 1931, and one of these boilers was installed in the . This was a time when water-tube boilers were being adopted in fast

turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin ''turbo'', meaning vortex) is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating e ...

ships, such as naval warships and passenger liners. There was also a shift to

oil firing An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

rather than

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...

burning. Oil had several advantages for a fast ship, particularly a warship that needed to combine both efficiency for long range with the ability to generate high power on demand when full speed was needed. Oil required fewer stokers, and a smaller crew required less space aboard given over to mess spaces. Refuelling was also quicker and cleaner with oil than with coal. Hyperion 1936

The Johnson boiler was the first of the

O-type boiler An O-type boiler is a form of water-tube boiler. It is named, like the D-type and A-type boilers, from the approximate shape of its tubes. They are characterised by single steam and water drums vertically above each other, with curved vertical ...

s, a class of water-tube boilers characterised by single

steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...

and water drums vertically above each other, with curved vertical water tubes to the sides forming an overall cylindrical volume. There is no grate at the base of this furnace space, so they are fired by liquid burners, rather than a solid fuel furnace producing

ash Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non- gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...

. The large radiant heating area available allows a combustion rate, for a given furnace volume, of around twice that for a contemporary boiler, such as the Yarrow. The end walls of the furnace may be either water walls with more tubes, or else simple firebrick. The small amount of brickwork for the Johnson design, without requiring a furnace base, was seen as an advantage by the Navy. The Royal Navy trialled a Johnson boiler in 1936, when the

H-class destroyer The G- and H-class destroyers were a group of 18 destroyers built for the Royal Navy during the 1930s. Six additional ships being built for the Brazilian Navy when World War II began in 1939 were purchased by the British and named the ''Havant ...

was built with two

Admiralty 3-drum boiler Three-drum boilers are a class of water-tube boiler used to generate steam, typically to power Steamship, ships. They are compact and of high evaporative power, factors that encourage this use. Other boiler designs may be more efficient, although ...

s and a Johnson, rather than the three Admiralties used for the rest of the class. This boiler had a water wall at the non-firing end. The initial design had poor circulation until external cold downcomers were added, increasing the weight by 10%.

Babcock-Johnson boilers

The Babcock-Johnson is the developed form of the Johnson design, constructed by

Babcock Babcock is an English surname. Notable people with the surname include: *Alpheus Babcock (1785–1842), American piano and musical instrument maker * Audrey Babcock American operatic mezzo-soprano *Barbara Babcock (born 1937), American actress * ...

. The end walls of the furnace are tube-walled and there are large external downcomers. The boiler and its exhaust uptake is enclosed in an overall downward air duct, supplied through an air preheater in the exhaust stack. Early versions of this design used a thick tube nest, split into two layers and with the

superheater A superheater is a device used to convert saturated steam or wet steam into superheated steam or dry steam. Superheated steam is used in steam turbines for electricity generation, steam engines, and in processes such as steam reforming. There ar ...

placed as axially-parallel tubes between these. Later designs had thinner tube nests of only four rows of tubes, with the superheater placed in the uptake to the funnel. Working conditions would be '850/850', with a working pressure of and a steam temperature of . The superheater would be placed in one side of the uptake, with a reheater between the high and low pressure turbines placed in the other.

Fairfield-Johnson boilers

The Fairfield-Johnson boiler is a further development of the Babcock-Johnson type. The working pressure of the boiler is reduced from around 58 bar to 30 bar, but the steam temperature after the supheater remains the same at around . The engineering change for these boilers is to reduce the work done in the boiler's steam generating tubes, in favour of increased superheating. Radiant heating of the boiler tubes is the same, but there is less convective heat transfer, giving a higher superheater gas inlet temperature.

References

{{Boilers Water-wall boilers Marine boilers Water-tube boilers Steam boiler types