Technical

Specification for the ex Castle Class Ships

Displacement - 1060 tons

Length - 252ft (77m)

Beam - 37ft (11m)

Draft - 10ft (3m)

Engine - 4 Cylinder triple expansion, fed by 2 water tube boilers, developing 2750 hp

Speed - 16kts

Ships Layout

A modified drawing from blueprints, with assistance from Dave Offiler

A couple of pictures of Adviser's engine

Info about the engine and machinery taken from an article by Howard Cox

(Full article HERE) © Howard Cox

The machinery spaces were unaltered from the day they were built in 1944. The main engine was an open crankcase four cylinder triple expansion steam reciprocating engine of 2750ihp and there was a reciprocating engine driving one of the dc generators, and a turbine the other one. Separate from the machinery space were two pressurised boiler rooms each with a Yarrow water tube boiler. In the days of convoy duty they would be sailed with both boilers fired and could achieve 16.5 kts but for this peacetime role only one boiler would be used on each trip and we travelled at 10 kts or so to and from station. To reach the stoke-hold you had to leave the engine room, go out on deck before entering through the correct set of air lock doors for the boiler in use. It was quite a rigmarole when you were in a hurry, particularly as you had to go through one door and close it, then open a vent and let the pressure stabilise, before the next door could be opened. Some 30 minutes ahead of a balloon launch we would start to get the engine ready by letting a little steam blow through to warm the cylinders and also to make sure no water that had condensed in the cylinders was trapped (which might cause a hydraulic lock and damage the engine). Five minutes or so before time the bridge would whistle down and ask if we were ready then on time the telegraph would ring for dead slow ahead and a clicker device would ring up the number of revolutions that the watch-keeper thought was needed. The telegraph also rang in the stokehold so the firemen knew when to open up more burners. Then we would have some half-an-hour of manoeuvring with the bridge calling for alterations in speed every few minutes, 50 revs, 55 revs, back to 50 revs and so on. The trouble was that we had no tachometer. There was a revolution counter but as that was showing some millions of revs it was far simpler to grab hold of part of the valve gear that was oscillating near the control station, watch the clock and count just like a nurse does when she checks your pulse. Making the fine adjustments the bridge expected was almost impossible and quite often we would just make a guess, open up or close down a touch but if it was for a stupidly small amount we would not even bother. The main engine was slightly different from the text book triple expansion engine in that it was four legged with two low pressure cylinders, but it had all the standard Stephenson Link valve gear. All this linkage was controlled by the reversing lever which acted through a steam driven servo motor so one didn’t have to be overly strong to shift the heavy gear from ahead to astern or to make the fine ‘notching’ adjustments for economical operation. Speed control was achieved by opening or closing the main throttle valve by a large control wheel just near the telegraph quadrant at the control station. The other principle valve was located on the bulkhead between the machinery space and the aft boiler room. This stop valve was normally left wide open but in the event of an accident or burst steam pipe a cable could be pulled from an emergency stop position on deck. I never saw the steam turbine running - I was told that as they were far too noisy and no-one liked them, so the Bellis and Morecambe reciprocating generator was always in use. With that running and the few pumps, some steam, some electric, that were needed to keep the ship going, these engine rooms were remarkably quiet. In summer with the skylight wide open we could hear everything that was happening on the afterdeck.

An animation of a simplified triple-expansion engine.

High-pressure steam (red) enters from the boiler and passes through the engine, exhausting as low-pressure steam (blue) to the condenser.It is a logical extension of the compound engine to split the expansion into yet more stages to increase efficiency. The result is the multiple expansion engine. Such engines use either three or four expansion stages and are known as triple and quadruple expansion engines respectively. These engines use a series of double-acting cylinders of progressively increasing diameter and/or stroke and hence volume. These cylinders are designed to divide the work into three or four, as appropriate, equal portions for each expansion stage. As with the double expansion engine, where space is at a premium, two smaller cylinders of a large sum volume may be used for the low pressure stage. Multiple expansion engines typically had the cylinders arranged inline, but various other formations were used. In the late 19th century, the Yarrow-Schlick-Tweedy balancing 'system' was used on some marine triple expansion engines. Y-S-T engines divided the low pressure expansion stages between two cylinders, one at each end of the engine. This allowed the crankshaft to be better balanced, resulting in a smoother, faster-responding engine which ran with less vibration. This made the 4-cylinder triple-expansion engine popular with large passenger liners (such as the Olympic class), but was ultimately replaced by the virtually vibration-free turbine.

Photos of HMCS Sackvilles engine, the basic engine in the Castle`s being the same as the Flower Class ships but with differences to controls and ancillary equipment