rms MAURETANIA,
1907, Cold Starting
CUNARD LINE
Ltd., Builders: SWAN, HUNTER & WIGHAM RICHARDSON. Newcastle on Tyne
by Stephen Carey, engineer, editing by Earl of Cruise
rms MAURETANIA © Stephen Carey
1 Overview of machinery spaces
1.1 Boiler rooms
MAURETANIA is (or was) a quadruple
screw Cunard liner fitted with 2 single-ended and 23 double-ended boilers,
operating at 195lb/in2. These boilers
are arranged six in 3 boiler rooms (4,3
& 2; note that Cunard numbers forward to aft compared to White Star
which numbers aft to forward), and five in No1 Boiler Room (the foremost one)
where the fine lines of the ship only allow 2 abreast at the forward end of
this boiler room.
No1 Boiler Room also houses the two
single ended boilers used for hotel services and auxiliary supplies in
port. The double-ended boilers are fired
for transatlantic passages up to full speed and primarily used for main
propulsion.
Combustion air for the boilers is
provided by forced draught fans, so for cold starting these have to be run up on
the shore electric supply before firing the boilers.
1.2 Coal bunkers
Coal bunkers are provided either
side of the stokehold furnaces in each boiler room to enable a ready supply of
coal for the trimmers and firemen to stoke the boilers. These bunkers form the double side of the
ship through all the boiler rooms (unlike Titanic which has transverse bunkers
either side of the transverse watertight bulkheads).
Ash chutes are provided to
discharge ash from the furnace bottoms overboard at regular intervals to keep
the stokehold clear of ash whilst at sea.
In port ash hoists are used to dispose of the ash to shore facilities.
The main steam pipes run the
length of the boiler rooms to the bulkhead stops in the centre engineroom for
distribution to the engines and auxiliaries.
Figure 1
Mauretania's stokehold prior to conversion
1.3 Propulsion engines
There are two high-pressure
turbines situated in the wing watertight turbine rooms, aft of Boiler Room No4. Steam from the main steam piping is admitted
to the high-pressure turbines, which then exhaust into the ahead low-pressure
turbines situated in the centre engineroom.
Exhaust steam from the low-pressure
turbine is directed to the vacuum condensers, situated in a further watertight
compartment aft of the turbine room, where it is condensed into feed water and
pumped back into the boilers.
Manoeuvring from ahead to astern
is carried out on the lp ahead and astern turbines, the hp turbines playing no
part in the astern operations. Steam is
directed either ahead or astern by means of a large manoeuvring valve driven by
a steam driven gear. The main exhaust
sluice valve for directing steam from the hp turbine to the condensers direct
(i.e. bypassing the lp turbines) is electrically driven. This bypassing is only used in an emergency,
as it is extremely inefficient to exhaust the hp turbines straight into the
condensers.
Regulating valves driven by worm
and quadrant gear via spindles operated from the starting and manoeuvring
platform, admit steam to the engines as required by the telegraph orders.
2 Electrical power generation
2.1 Main generating sets
The vessel is fitted with 4 375kW
110Vdc main turbo-generators driven by Parsons steam turbine prime movers. These sets are situated two to a watertight room
aft of the condenser watertight room, separated by a centreline watertight
bulkhead, ensuring maximum redundancy from damage. As the vessel is not fitted with either
auxiliary or emergency generators, it is assumed that the watertight
arrangements of these compartments would ensure the reliability of the
electrical generating supply.
Steam at a pressure of 195lb/in2
is fed to the turbines and exhaust steam is directed in port or at start up to
the auxiliary condensers. At sea the
exhaust steam is directed to the surface and/or direct contact feed heaters to
extract the remaining energy from the exhaust steam and deliver it to the feed
heating system. This configuration gives
a total installed power of 1.5MWdc, with three sets covering the full steaming
load and one in stand-by.
2.2 Auxiliary/emergency generating sets
There are no auxiliary or
emergency generating sets on MAURETANIA.
Figure 2
Generator room and switchboard
3 Firing up the boilers
The engineers start the required
forced draught fans on the shore power supply.
Assuming that for a main generator to run we need at least all the fires
in one boiler room lit, one FD fan is started to supply the furnaces in one of
the main boiler rooms. The firemen are
set to work in this Boiler Room to lay fires in all required furnaces. Once lit, the boiler draft is adjusted by
dampers and the fires start to heat the water in the fire-tube boilers. Water-tube boilers are much more efficient
and faster starting than fire-tube, but hadn’t been invented at this time. It would take around 12 hours to raise steam
to manoeuvring pressure.
It’s now 12 hours on, and we have
around 190lb/in2 at the main stops to the main steam lines to the enginerooms. The main stop valves of the boilers are open
to the main steam pipe during firing in order to bring up the piping
temperature to that of the first boilers lit, such that the piping and valve
drains clear the lines of condensate, which can damage reciprocating and
turbine machinery. The remaining boilers
are banked with main stops closed until main power is available and more steam
is needed.
4 Starting the generators
4.1 Auxiliary seawater pumps and condensers
In order to start a turbo-generator,
the exhaust steam from the engines is directed to an auxiliary condenser, of
which there are two; one in each of the watertight auxiliary condenser rooms
situated either side of the centre turbine room. The seawater passing through this condenser
condenses the exhaust steam into water, thereby dropping its pressure. Without this the engine would trip on high
exhaust backpressure, as the exhaust steam has nowhere to go. In addition the condenser is supplied by an
auxiliary air pump (or vacuum pump) to increase the vacuum by removing
non-condensables such as air and CO2 in order to drop the exhaust steam
pressure further.
The auxiliary seawater pumps are
steam driven and situated in the same room as the auxiliary condensers. The sea suction and discharge to condenser
valves are opened prior to starting.
With the pump cylinder drains
open, steam is admitted to the pump, which gains speed and starts to circulate
seawater through the auxiliary condenser to overboard. In the same way the auxiliary air pump is
started in order to draw a vacuum. Once
these two pumps are up to speed we are ready to start the main generators.
4.2 Starting the main generators
As we will soon be consuming
steam, we will also need to be able to start a main feed pump to supply the
boilers with feed water as required – see later.
The generator bearings are forced
lube type, so first we start a LO pump (again steam driven, as are nearly all
the engineroom auxiliaries) in the same way as the seawater pump above. The LO pump supplies oil for the bearings as
well as control oil for the generator throttle valve. In this way, a failure in LO pressure will
automatically trip the generator to avoid damage to the bearings.
After warming through the generator
steam lines and opening the turbine exhaust to the auxiliary condenser, the
first and subsequent generators are warmed through and run up to a speed of 1200rev/min.
On the main switchboard (of which
there are two, joined by a bus-tie breaker), the breaker is closed for the
generator in question and the shunt field regulator adjusted to give mains 110Vdc
voltage. There is no need to synchronise
dc machinery, unlike alternating current machines. Once the generator has settled down on the
board, the shore breaker is opened to avoid back-feeding the shore supply as
the main generator loads up.
We can now put the other
generators on the board as required. We
are up and running on main power and can connect other feeders via the main
switchboard distribution as required.
As you can see, this is quite a
long job compared to a modern diesel powered ship (though steamships still take
some time). A blackout on a modern
motorship can be restored within a few minutes, whereas a steamship takes much
longer.
5 Starting main engines
We now have power for all the
forced draft fans required to fire all the boilers necessary for starting the
main engines and getting the enginerooms ready for sea.
First we have to get the propulsion
exhaust steam system arranged in a similar way to that of the generators but,
in the case of the main engines, the auxiliary condenser is nowhere near big
enough to handle the exhaust from the propulsion engines.
For this we need to draw a vacuum
on the main condensers, of which there are two, one either side of the watertight
condenser room aft of the low-pressure turbine room.
5.1 Main seawater pumps
As with the auxiliary condenser,
we need seawater to condense the steam and drop its pressure to avoid exhaust backpressure
on the engines. These are pretty huge
and are driven by compound steam engines.
There are two pumps per condenser (total of four) arranged adjacent to
the condensers in the watertight main seawater circulating pump room aft of the
condenser room.
The main sea induction valves and
overboards on the ship’s side are opened for each pump and, as with all steam
engines, the main seawater pump engines are warmed through with the drains
open, then slowly started up until they are at full revs. Once the pumps are running, seawater passes
through the condensers and discharges overboard – that’s the large overboard discharge
that can be seen on any steamship up to the present day.
5.2 Main dry-air pumps and wet-air pumps
The air pumps (called vacuum
pumps these days) evacuate air and water vapour from the condensers and draw a
vacuum in so doing. This improves the
exhaust flow from the engines and also extracts the maximum energy from the
steam. They are situated in the main
circ room inboard of the main circ pumps and are of course steam driven. They are started in the usual way, and left
to draw a vacuum on the condensers, usually around 28.5in with an atmospheric
pressure of 30in. Water from the wet-air
pumps is returned to the feed tank under the condensers, as is air from the dry-air
pumps.
5.3 Main generators
Now that the steam and feed
system is up and running, we can extract the energy from the main generator
exhaust by redirecting it from the auxiliary condenser to the contact or direct
feed heater, through which the condensate from the feed tank passes via the
hotwell pumps (see later) to mix with the generator exhaust steam. This imparts heat to the feed water to avoid
wasting the energy from the generator exhaust.
5.4 Main engines
By this time the engineers (we
assume we are not doing this on our own) will have engaged the electric turning
gear motors on all four shafts, as well as starting the turbine forced lube oil
pumps (steam driven). The engines are
kept turning until required for use, whence the gear is withdrawn to avoid
damage to it in the event of starting a turbine with it engaged. Gland steam is assumed to have been fitted
(no mention in the Engineer & Shipbuilder reprint I have) and will be
started up to extract leakage steam from the turbine shaft glands, and condense
it back to the hotwell drains.
The hp turbines are kept warmed
through ready for working up to speed on passage, with manoeuvring steam admitted
to the lp turbines with the drains full open and the exhausts open to the
condensers. At first the main steam
valves are cracked open until everything is warmed through, whence they can be
fully opened.
Once the turbine drains are
emitting steam, we can call the bridge and ask if the propellers are clear for
a slow turn ahead and astern. Once this
is given, the manoeuvring valve is set to ahead position (which isolates the
astern lp turbine) and the main steam regulating control valve cracked open at the
starting platform at the forward end of the lp turbine room. The engine will start to turn ahead at low
revs. After a few turns of the shafts ahead
the regulating valve is closed and the manoeuvring valve set to the astern
position (which isolates the ahead lp turbine).
Again the regulating valve is cracked open and the astern turbine turned
for a few revs at low speed.
We are about ready to go, and
test the communications between the engineroom, boiler rooms and bridge so that
we are ready for sea service. Around the
same time an engineer is dispatched to the steering engine room to warm through
the steering engines and test the rudder from midships to 30 degrees port, back
to 30 degrees starboard then returning to midships.
Figure 3
Mauretania starting platform
5.5 The feed system
Steam from the condensers that
has condensed into the hotwells under the condensers is returned to the boilers
via two feed heaters using the sets of hotwell pumps located under the main
condensers. These pumps deliver the
condensate to the surface feed heaters
located in the auxiliary condenser rooms.
These heaters are fed with exhaust steam from the auxiliaries (the pumps
mentioned above, such as seawater, air pumps, lube oil pumps etc.) and this steam
heats the feedwater passing through the shell and tube heating elements.
From the outlet of the surface
heaters the feed water is passed to the 2nd of the two feed heaters,
which is a direct/contact heater
where the water comes directly in contact with exhaust steam from the main
generating sets. These heaters are situated
high in the engineroom above the astern turbines and act as a deaerator once
the air vent at the top of the heater is opened up to the main condenser to
extract undesirable gases (CO2 and O2), which can cause corrosion problems in
the boilers. In this heater the generator
exhaust steam condenses in contact with the boiler feed water stream from the
hotwell pumps and is then extracted under gravity by the main feed pumps and
sent to the boiler distribution mains as required. Mauretania did not have automatically
operating feed control valves, so this was a manual operation. Its height ensures that there is sufficient positive
suction head for the main feed pumps that feed the boilers. All is now ready to go, with the stokers
bending their backs to raise steam on all the boilers required for leaving
port.
6 Getting under way
In response to the bridge signals
on the engineroom telegraphs, the lp turbines are manoeuvred accordingly as above
and the ship departs her berth and heads for the open sea.
7 High-pressure turbines
Once the ship is up to full
ahead, and prior to full away, the two high-pressure turbines (which have been
kept warmed through with their exhausts directed to the two ahead lp turbine
inlets) are started via their regulating valves and brought up to speed. The wing turbines (and shafts) are now
driving ahead and adding to the thrust of the lp turbines on the inner
shafts. The steam is now passing from
the boilers to the main steam lines, through the hp turbines, into the lp
turbines and exhausting to the condensers, from where it is returned to the
boilers as above in a closed feed cycle.
Full power can now be worked up once full-away is rung on the
telegraphs.
We’re done, we’ve been down below
on a coal-burner for over 12 hours, and it’s time to go to bed before having to
get up again and win/keep the Blue Riband of the Atlantic.
Figure 4
View between the lp turbines and starting platform
8 Coal-firing vs oil-firing
Coal-firing was a dirty, messy,
labour-intensive way to feed a furnace.
As well as bunkering and firing the boilers, disposal of the ash was an
additional burden on the stokehold staff.
“Coaling ship” was an “all hands” task where everyone turned to so fill
the coal bunkers via coaling ports in the side of the ship.
Oil-burning on the other hand is
far less labour-intensive, with the bunkering taking place via a hose from a
bunker barge in to the same bunkers as the coal was previously.
A coal-fired ship needed some 250
stokehold staff to fire and tend the boilers, whereas ships like Mauretania
when converted to oil-firing only needed some 60-odd stokers.
Figure 5
Disposing of ash from a furnace
Figure 6 Filthy conditions in a coal-fired stokehold
Figure 7 MAURETANIA stokehold after conversion
Figure 8
MAURETANIA boilers after conversion
From the pictures above, compared
to the filthy conditions in a coal-fired ship, can be seen the huge improvement
in working conditions once the stokehold had been converted to oil firing.
In addition, firing on oil was
far more efficient, and the power output of MAURETANIA improved substantially
after conversion, as did the overall Specific Fuel Consumption. As there was no requirement to discharge ash
overboard, the ship was much cleaner and – even though the environment was not
much considered in those days – oil firing opened up the world shipping fleets
to better environmental conditions. The
volume of smoke seen issuing from the funnels of these large passenger ships
also reduced dramatically; an oil-fired boiler is designed to run cleanly, with
no smoke other than a haze at the funnel tops, whereas it was difficult to
avoid smoke – especially whilst manoeuvring – from over 20 boilers fired on
coal. The coal fires are slow to react
to changes in steam demand and draught requirements, whereas oil-firing can
react immediately.
One procedure that didn’t really
improve was the length of time taken to raise steam in fire-tube boilers, and
it was some years before the next major trans-Atlantic steamship was built
using water-tube boilers. This was the
Empress of Britain, which will be discussed in a further document on starting
these large liners from cold.
Figure 9 Plan of boiler rooms up to the
ER bulkhead
9 Profile and plan of boiler rooms
On the view
in Figure 5 can be seen the extent of boiler rooms
2,3 and 4, with a hint of Boiler Room 1 at the fore ends. The boilers are installed 6 to a room.
10 Uptakes and ash ejectors
The uptakes
can clearly be seen, illustrating that all four funnels on this vessel served
the boilers (unlike the TITANIC, whose aft funnel was a ventilation shaft.
Zooming in
on the drawing shows the ash ejectors in boiler rooms 2&4, and the ash
ejector pump is shown in boiler room 2.
11 Auxiliary feed pumps
There is an
auxiliary feed pump either side of the watertight bulkhead between numbers 2
& 3 boiler rooms. No1 and No4 boiler
rooms also have an auxiliary feed pump and ash ejector.
12 Main steam lines, RD fans and escape ladders
On
the profile view, note the main steam lines running the length of the ship
above the boilers, the forced draft fans mounted on the Orlop Deck. Also the vertical ladders the same as the
TITANIC where they stokers can get out of the stokehold if the watertight doors
are closed.
Figure 10 Plan of machinery spaces
Figure 11 Elevation of machinery spaces
13 Plan and elevation of machinery rooms
The views in
Figure 5 and Figure 7 show the forward engineroom bulkhead on which
are the bulkhead stops for the two main steam lines exiting from No4 boiler
room. The bulkhead stops are actuated by
Brown’s steam engines as they are too large to manually operate. The engine overspeed governor can act on
these valves and shut off the steam in the event of overspeed.
The turbines
and equipment are mirrored for each pair of shafts. For the notes below we will consider the port
side pair of shafts to avoid repetition.
14 Steam lines
The steam,
after passing though a strainer to remove particles, is directed either to the
hp turbine via the pipe passing through the watertight longitudinal bulkhead,
or aft to the lp turbines via the large double manoeuvring valve shown at Fr 94. The starting platform from where the engines
are driven ahead and astern is located at the forward end of the astern lp
turbines and can be seen around Fr 104.
The starting wheels comprise a large outer wheel for the bulkhead stops,
and a smaller inner wheel for the manoeuvring valve. The levers for controlling the turbine drains
and sluice valves are close by.
15 Turbine isolation
Taking the
port hp turbine as an example, there are two exhaust pipes exiting from the
turbine casing, both of which have large sluice valves installed. The after larger one (75”) directs hp exhaust
steam into the inlet of the lp turbine, which is the normal mode at sea. The other smaller (60”) sluice valve directs
the exhaust straight to the condenser (in the event that the lp set is out of
service) and is therefore normally closed.
Whilst manoeuvring, both sluice valves are kept shut to avoid steam back
flowing from the lp turbines into the idle hp turbines.
The exhaust
from the lp turbines to the condensers is the large length of piping shown at
the aft end of the ahead lp turbine, which passes through two watertight
bulkheads and into the main condenser.
16 Main manouvering valves
Around Fr 93
and in line with the steam lines to the lp turbines can be seen the double
outline of the manoeuvring valve that directs steam either into the ahead lp
turbine (the larger pipe) or the astern turbine (the smaller pipe).
17 Feed water pumps
Along the
forward bulkhead in both hp and lp engine rooms are arranged the main feedwater
pumps. These pumps draw from the
direct/contact feed heater mounted on the flat above the turbines
18 Auxiliary equipment
A set of
evaporator machinery for producing fresh water is installed in each hp turbine
room, while aft of these are the fresh and condensed water pumps in the port
room, and refrigeration machinery in the starboard hp turbine room. Space is therefore limited in both these
rooms.
In the lp
room are fitted the the hotwell, bilge, oil, water service, fire and sanitary
pumps.
In the
Auxiliary condenser rooms can be seen the condensers themselves, the condenser
seawater pumps and air pumps, the main and auxiliary feedwater filters and the
surface feed heaters. The Stone-Lloyd
pumps shown outboard in the port room are for operating the watertight doors.
19 Main condenser room
In the main
condenser room are installed the main condensers. Note that there is no centreline bulkhead in
this room. Mounted under the condensers
are the hotwells for collecting the condensed steam, and the hotwell pumps
which pump the condensate into the feed system.
20 Auxiliary machine rooms
Aft of the
condenser room, the next watertight compartment contains the two large main
condenser seawater-circulating pumps, the main wet-air pumps and the dry-air
pumps for creating the vacuum on the condensers. The dry-air pumps are mounted one set above
the other.
Above the
auxiliary machinery room is situated the turbo-generator room and its attendant
main switchboard.
21 Shafting and propellers
From the
thrust bearings mounted at the aft end of the lp turbines (the engines which
are coupled to the centre shafts) the two propulsion shafts are arranged in the
shaft tunnels and exit the ship via the stern tubes. There are several intermediate bearings
(Plummer Blocks) along the length of the shafting which are splash lubricated.
Written by Stephen Carey
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