By the start of WW1 the greater majority of RN ships were driven by steam turbines. Some older vessels such as monitors, sloops and smaller craft still had reciprocating steam engines (one class of sloop still had steadying sails!)

Some of the earlier ships fitted with turbines had a direct drive from the turbine to the propeller shaft. Before long this was changed to a geared reduction drive to the prop shaft.

Steam Cycle in a Machinery Unit

Steam is supplied from the boilers to the turbines, where it is expanded from pressure down to vacuum. Turning from steam to cool water in the process. Vacuum is maintained in the main engine condenser by
a) Sea water being pumped through the condenser tubes by the main circulating pumps(a steam piston driven rotary pump)
b) Steam ejectors, which is a steam supplied venturi system, extracting vapour from the main condenser
c) An 'Air Pump'.(Probably another Weir pump or similar )

The latter is somewhat misnamed as it extracts the condensed steam and pumps it into the main feed tank.

Vacuum conditions are maintained in order to maximise the energy available in the steam supply.

The boiler feed pumps( Weirs again) take water from the main feed tank and raise it to above steam pressure, and pass it through a steam fed heater, to maintain the boilers water level.

During operation of the above cycle a certain amount of the water involved is lost as leaks, one way and another ( could amount to several tons per hour). To replace this loss a piece of kit known as an evaporator is used. This takes in sea water and steam is used to boil it .The vapour given off is condensed and( if the evaporator plant is steamed properly) will produce pure fresh water for about 23 hours/day .The odd hour it is shut down for descaling.

This water can be put into
a)an auxiliary feed tank ,as make up feed water.
b)or into ships domestic supply fresh water tanks.

The losses from the steam system show as a reduction in the main feed tank level , and so , make up feed water is run into the main feed tank from the auxiliary feed tank.

Steam Turbines
(there were several different designs, the description is of a Parsons one)

A turbine is a system of rotating blade discs upon the turbine shaft or rotor, this rotor operates in a casing inside which are discs of fixed blades.

Steam comes from the main engine throttle valves, passes through a nozzle set, and hits the turbine blades. The blade discs are arranged so they alternate, rotor blade disc, casing blade disc ,and so on. In passing down the line of blades the steam expands as it gives up energy in rotating the shaft. To get more power as the steam expands the rotor /casing blading is increased in size accordingly.

In order to maximise engine room space, the turbine is divided into a High Pressure Turbine section, when the steam exhausts from this it passes to a Low Pressure Turbine Section and thence to the Main Condenser, which is underslung to the LP unit. The astern turbine is usually at one end of the LP set.

In this way the two sections are alongside each other, their output shafts each having a driven gear, mating with the main gear ring which drives the propeller shaft.

A set of Weirs pumps would supply oil to the turbine bearings.

On propeller shaft there is the main thrust block, which takes the reaction of the propeller to the hull, propeller shaft bearings, the stern gland and lastly the propeller.

Just for example the battlecruiser Repulse, 30 knots with 4 screws and 120,000 shaft horse power. Fuel oil capacity 4250 tons, which would probably last ,maybe two weeks.

Engine Room Operation

To operate an engineroom unit would require the following.
Chief Engine Room Artificer, in overall charge of one set of boilers, engines etc.
Petty Officer Engine Room Artificer as Throttle Jockey
Two stokers for general duties & propeller shaft monitoring.

The throttle jockey ERA earned his money, when manoeuvring. Main engine throttle valves are unbalanced and require opening against the head of steam pressure. Throttle valve size could be as much as 10" diameter . There would be ahead, astern and cruising throttle valves.

Engine Room telegraphs would indicate the required revolutions ,ahead, astern as required. The ERA on the throttles acknowledged any changes back to the bridge. While watching or otherwise operating the throttles, the ERA would also be checking an array of gauges, giving things such as boiler steam pressure, steam pressure (after the throttles) to the engines, steam to the ejectors, condenser vacuum, engine bearing oil pressure, feed tank levels and so on. Log readings of all important parameters as listed would be taken on an hourly basis.

Most folk would think engine and boiler rooms to be warm places, but in winter, in the North Sea or North Atlantic, it can be cold ! :-Outside air temperatures come down with the ventilation air supplied, though it is usually possible to get out of the worst of it.

Steering Gear

There is a whole host of other items of machinery required to send a ship through the water, but this one stands by itself.(HMS Forth had a set that would have been typical of many earlier ships)

In an after corner of the engine room was a twin cylinder high speed steam piston steering engine. Fitted with crankshafts at 90 degrees to each other, it would thus start from any position. From the wheel house to the engine room was a hydraulic system, that moved a steam control unit in response to the ships wheel. This unit allowed the steering engine to reverse direction very rapidly. From the crankshaft of this engine was a set of shafting and bevel gears that transmitted power down to the tiller flat, wherein was the rudder head.

At the end of the shafting was a large leadscrew (about 6" diameter and some ten feet long ),with a left hand thread on one end, right hand thread on the other. Two threaded handed blocks ran on the threads and each was connected by a steel links to one end of the quadrant on top of the rudder head shaft. As the leadscrew revolved the rudder was turned .

As with most items of naval engineering, arrangements have to be made for action damage, such as duplication of pipework or more than one of an item such as a pump.

If the hydraulic system from the wheel house failed then the steam engine could be manually controlled. In response to phone or other messaging.

If the steam engine failed, then an older technology came into play. The dog clutch connection to the steam engine could be undone ,and a secondary clutch connection made , -- to a ships wheel , -- such as would have graced a clipper ship. Three wheels, all polished mahogany and brass, on a common shaft . Six seamen ,one either side of each wheel, was the motive power. Under heavy manoeuvring, they would last about twenty minutes, and a standby team of a further six was on hand to relieve them. So the two teams would go turn & turn as they became worn out.

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