Y-100 Engine

The Y-100 or Yarrows-100 engine was the result of an invitation to tender a design for the Type 12 Frigate. Yarrows won the order with a combination of two Babcock and Wilcox American 550 psi boilers and a pair of English Electric Turbines with a double reduction gearbox.

The design was popular and with modifications was also constructed in Canada and Australia. The design included a reversing turbine as was standard and also a pair of cruise turbines, though in the event the gearing mechanism for these did not work properly and the cruise turbines were rarely used and later omitted or removed from most ships.

Although to get the engine as compact as possible it ended up with no inherent redundancy in the event of action damage since boilers were in the same room together and adjacent to the single engine room, the system proved very effective, even without the cruise turbines, and went on to power the Type 14 second Class Frigate in the configuration of one half the Y-100, and the County Class Destroyer as a cruise alternative to her gas turbines.

Based on war and peace proven designs the Y-100 proved a very reliable and efficient power plant that took up relatively little space; the failure of the cruise turbine was never addressed though and while that was not too much of an issue in peace time it would have hampered the ship's while carrying out slow convoy escort work in war.

The 550 psi Babcock and Wilcox boiler that formed part of the partnership that was the Y-100 Engine.

1 - Fuel Feed
2 - Sprayers
3 - Lower water collector
4 - Super Heater
5 - Water heating pipes
6 - Steam Collector
7 - Furnace
8 - Upper water collector
9 - Super heated steam output

One of the main tasks of the boiler, apart from making steam, is to seperate the steam from the water. While steam is in contact with water it contains a high moisture content, termed saturated steam and in the engine that moisture condenses out as water droplets that lower the pressure of the steam, and harm turbine blades. The boiler draws steam off the water and passes it back through a seperate tube system where it is heated again to form super heated "dry" steam.


The Y-100 generated 15,000 SHP on each shaft, 30,000 in total, 5,000 SHP in reverse. As yet I have no figure for the cruise turbines.

The main turbine was a Curtis Wheel type with 8 Impulse Stages (Rateau?), each weighed 20.2 tons and the height of the largest blade was 152mm with a wheel diameter of 660mm. Steam flow at the main stop valve was 54 tonnes per hour and ideal operating speed was 5,750 rpm forward, 4,152 astern. The double reduction gears dropped the propellor RPM down to about 225 rpm at full power, this allowed for a comparitively large propeller size and accounts for the max speed of 30 knots at a lower than normal 30,000 SHP. (The light destroyers of RN WWII operated at 40,000 SHP)

The Babcock and Wilcox two drum boilers were each self contained with their own force draught air feed and flue, though both flues were contained within a single funnel on all RN ships, (on some Canadian ships such as the St Laurent the funnel was split into two to fit around a helicopter hanger). Super heated steam was passed overhead into the Engine Room and returned from under the turbines back into the boiler system.

Steam supply was also tapped off for two 400KW (later 500KW) Turbine-Alternator pairs, one in each machinary space for primary electrical generation, this was 440V 3 Phase AC. Steam was also used to generate heat for the air conditioning, supplied to the galley for the ovens and to the laundry.

Time from cold to sea ready was four hours. The system was self sustaining in that it replenished it's own feed water from sea water using evaporators and also provided ample excess to provide for near unlimited usage by the cre. A Donkey Boiler provided domestic services when the main boilers were rung off, or the ship could hook up to shore steam where available.

The early fueling of the Y-100 was done with FFO or Furnace Fuel Oil, a thick black waste product of petroleum production. It needed to be heated before it would flow like a liquid, including for fueling and for feeding to the engines. As Gas Turbine ships began to be introduced the FFO ships were re-fitted to use Dieso (Diesel Oil) so that a single fuel could be used across the RN, although at the time of the Falklands the Flagship Hermes was still on FFO, and possibly others.

The Y-100 equipped all the original Type 12 ships, the 12(M) Rothesay and the first batch of 8 12(I) Leanders. The second batch of Leanders received the modified Y-136 engine which mainly included modifications made possible by the switch to Dieso resulting in less complex control systems and hence a somewhat quieter engine.

The final batch of Leanders received the Y-160 engine which incorporated remote monitoring and control systems, this on the whole negated the need to man the main machinary spaces while the ship was closed down for nuclear transit, though the Y-160 was never a fully automated system.

The Y-100 plant sacrificed survivability for compactness (Bulkhead between Boiler Room and Engine Room has been reduced for clarity)
The above view is a work in progress; I would welcome any inputs and corrections, in particular I would like to be able to add the various steam and wate feeds with a view to producing a moving model.

I had the opportuninty to visit HMS Plymouth and took some photos around the Engine Room (The Boiler Room was our of bounds sadly). Where I can I have marked the drawing up and linked in some of the photos, I have more but as yet have not been able to work out where they go!
Below I have added the photos I cannot place, if you can help I would appreciate it.

Turbo Fire Pump according to the sign.

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