|S/S Diomed` Built 1922 Workman & Clark & Co,
Belfast. For China Mutual Steam Navigation Co.
Although it is hardly possible now to envisage the performance of a
Steamship in the year 1866, the Blue Funnel Line proudly hold the figures
of the trial trip of the first AGAMEMNON to obtain a speed of 10 ½ knots
from the use of just over 20 tons of Coal per day; this seems a wonderful
achievement until comparisons are made. One can imagine that the Coal used
was Kinglassie or Auchengeich, each of 14,500 B.T.U`s at a cost of
possibly 13/6d. per Ton delivered on board.
The same Ship, however, must be the deciding factor in comparison, for in
later years, the company were the Pioneers of the Scott-Still engine,
fitted into the ship DOLIUS (half-motor, half-steam), which traveled at a
speed of 11 knots on 11 tons of diesel oil per day, but possibly carrying
at least two or three times the amount of cargo.
In this simple comparison, one must remember that in the intervening
years, much effort and ingenuity were applied to increase the value of
coal, as burned under sea conditions.
In the early years and up to the end of the last century, the single-
ended marine type boiler was in common use, under natural draught
The speed of the ship was dependent on engine design and boiler pressure
carried, but the burning of coal for heat supply could only be governed by
area of fire- grate and incidentally draught pressure, at fire, was
governed by the length of the funnel. It is interesting to note at this
point that “Blue Funnel” was known throughout the world in those days, not
only for the colour but the height of the funnel. Even up to the First
World War, the old TELAMON was an outstanding of this, until she was
converted to forced draught and had two strakes removed from her funnel –
a matter of some 12ft.
The one apparent attempt to saving coal was the fitting of retarders in
the boiler tubes. These, as they were named, retarded the passage of hot
gases, being spiral in make and action, thereby aiding distribution and
dissipation. Efficiency, however, was somewhat neutralized by the fact
that they had to be removed periodically at sea for the purpose of tube
cleaning by long flexible tube brushes; consequently a fire had to be put
out of action during this process.
Prime factor in the efficiency of round voyage speed and consumption in
those days, was the supply of the best steam coal of high B.Th. U. value.
One may quote a ship of this kind in the old ULYSSES, built about 1890 and
sold to Japan in 1912. She was said to posses the largest single-ended
boiler ever built and sufficient steam to propel a ship of 5000 tons at
about 11 ½ knots on 30 tons of coal per day.
The desire for more speed began at the turn of the century and Alfred Holt
& Co had built their first steamers:- four in number, with double ended
boilers designed for 190 lb. per sq. in. pressure and fitted with a forced
draught system of air supply (Howdens in that day).
Within certain limits one could say that this was the infancy of burning
coal in an efficient manner, for the pressure of air supply “regulated”
the speed of burning and the supply of heat; necessarily there was better
control and more uniform boiler pressure at the engine. This in turn
encouraged the design of ships with finer lines and a very considerable
effort to improve propeller design. This reference would be more to the
point if we were discussing “Slip” rather than coal.
Again in 1906, the company first embarked on the building of twin engined
ships, known as the “Antilochus” class and it may be worthy of note that
the name of the class gave 42 years of service to the company. These ships
were designed for capacity purposes, 9,000 – 10,000 tons of cargo, carried
at an average speed of between 12 – 13 knots with a reserve of power in an
extra single – ended boiler –all at the cost of about 70 tons of coal per
One could be fairly definite in saying that up to the beginning of the
First World War the company obtained its desire for efficiency from the
improved designed of boilers, engines and the ship itself.
The LYCAON class built in 1913 had a regular speed of 14 knots for the
round voyage on a consumption of coal of about 65 tons per day.
The CALCHAS of an earlier class averaged a speed of 13 ¾ knots from
Australia, during wool sale time, on 70 tons of coal and compared
favorably with another company, whose ship had a greater capacity of
engines and boilers.
From about 1912, one can trace the change-over from the ”Shovel Engineer”
to an Engineer who had to know the B. Th. U's. of almost every known coal
supplied throughout the world, certainly those bunkered by the company as
far a-field as Japan, Java, Australia, South Africa, U S A, and including
the various European coals.
At that time there was started in the office what was known as the”
Three-Year Average”. A very near compromise of figures was made between
ships of any one class against each other, and comparable figures set
against any other class. With this “long term” comparison, a fairly true
picture was gained, covering all variations of weather (Monsoons, Gales,
etc) plus what engineers were most concerned about, the qualities of Coal.
This interest would certainly have developed with greater momentum, if the
First World War had not intervened. But when the safety of human life and
ships in general were at stake, one could not be expected to apply the
niceties of Coal- saving and general efficiency.
One might recall the fact that the THESEUS, designed for 13 ½ knots, was
known to escape from a submarine at a speed of
16 ¼ knots, but what her Coal consumption would have been at that speed
for even a short time, nobody then bothered or would have known.
Even so, at that time the Blue Funnel Engineers carried into practice
their knowledge of the burning of Coal by the
judicious use of air pressures, thereby reducing to a minimum, the amount
of black smoke (unburned Coal) emitted from the funnel. This loss of fuel
proved its own menace in the presence of submarines.
So important was this subject at a later date that at the beginning of the
Second World War the company sponsored a school in Liverpool to teach
firemen the extreme value of efficient burning of Coal – and the need of a
clear sky above the funnel of a steamer.
One thing gained from the First World War was the development of the
Turbine by the Royal Navy as a means of propulsion of ships. The immediate
outcome was the dream of the application of this invention in ordinary
Merchant ships. This change to propulsive power, and the threat of the use
of the Oil engine, added a comprehensive urge to the efficiency of “old
faithful”. The reciprocating engine. So Coal came into the forefront and
B. Th. U’s. were a matter of vital interest to the engineer whose main
object was to justify its continual use.
Boilers were improved in design, a greater number of fires were fitted,
heating surfaces and pressures were raised by 40 – 50 lb, per sq. in.
above the previous 175 – 180 lb. Superheat also – probably used in navel
vessels first—was installed in marine boilers (Schmitt design). This
invention also increased the speed of burning with Coal. Superheat
elements occupied quite a large percentage of the area of the boiler tubes
so that mechanical means had to be used for the cleaning of tubes. Parry's
blowers were used effectively on the larger area type of tube but with the
reduced diameter for the purpose of increasing heating surfaces, a lance
blower was designed, which as its name implies, sent a lance of
superheated steam ( dry of course) through every individual tube.
In all this preamble of progress, what of Coal? With a fleet of well over
70 ships (in the early 20`s) of capacities and speeds varying over a
fairly wide range, it is well understood that an enormous amount of data
was gathered from every quarter.
Ships traveling the world drew their bunker Coal from many countries and
each of these Coals was studied for its own peculiarities in practice and
theory; samples of each was brought home to undergo tests of calorific
values, ash percentages, etc., etc. at the analytical chemists`
laboratory, started by the company for the purpose.
With the previous knowledge of the “ three years average”, the compilation
of data was carried to a fine art and by 1924, every ship’s data of
performance were reduced to a “ unit figure “ of “ cost per ton-mile “ and
this was plotted every voyage against the ship, such a true comparison of
engine performance was shown that one could almost define the source of
the Coal supplied throughout a voyage, also the varied weather conditions
With the ship’s design was established a “ theoretical coefficient of
efficiency”. This covered the “block coefficient of the lines of the
ship”. Boiler efficiency (as high as 84% was reached in actual practice
against 87% theoretical) covered heat losses due to radiation and
diminution of superheat from boiler to engine, propeller design and
anticipated slip under normal conditions of weather and currents.
So the competitive instinct was aroused in engineers to arrive at or beat
the theoretical efficiency on the percentage basis, and the excellence or
otherwise of any ship was proved by a voyage performance of 90 – 110 %
efficiency as against some which, whatever effort was given to the
betterment of their failings, never had a greater efficiency than
somewhere in the region of 80 %.
Whilst all this accumulation of data was going on in the mechanical side
of the office, the company was by no means idle in the proof of “practice
“ on the spot. An experimental plant was erected in Birkenhead in 1922,
comprising a single-ended marine boiler, condenser, necessary pumps, water
tanks and a de-super-heater (one of the first of its kind) used to
dissipate the power developed in the installation. Samples of every know
Coal were delivered to this plant and reported on, being used under as
near sea conditions as possible. The data obtained and compiled were such
that engineers at sea would need to give quite a lot of attention to any
particular Coal supplied to them to approach the comparative figures
arrived at for the plant, such as lb of Coal per sq. ft. of grate area,
lb. of Coal per output of lb. of steam per hour, and ash percentage,
proving the completeness or otherwise, of the burning of Coal.
With this thought of “ complete combustion”, the company sponsored the
design of a “rotary furnace” which it was hoped could be adapted to each
furnace of a marine boiler at sea. The experimental boiler was fitted with
external mechanism, which burnt the Coal in an external rotating drum
delivering only the hot gases to the furnace and uptake of the boiler.
With mechanical Coal feeding of the hopper type, almost complete
combustion was obtained and the results gained in the experimental stage
were very convincing. However, the mechanical adaptation of gearing, back
draught control and finally the disposal of almost liquid ash (due to the
high temperatures obtained) squashed any idea of building such a
contrivance on a ship.
Again, about this time Powdered fuel was being universally discussed and
many shore plants were proving that this manner of Coal burning was
proving successful not only from the complete combustion point of view,
but the possible use of Coals of the lower calorific value and the
consequent saving in the cost of Coal a vital item if one considers the
tonnage consumed per ship and the overall total of many Coal burning
This experiment was carried out as far as the drawing- board, on which the
stokehold of an existing ship was planned to be fitted out with duplicate
crushers and independent pulverisers at each furnace with a complete
system of air supply. Here again the practical side of the experimental
plant indicated that the addition of many mechanical devices required and
their maintenance would make the installation prohibitive; these factors
plus again the disposal of molten ash, and incidentally the increase of
fire risk where powdered fuel was concerned, decided the company against
Speaking of experiments, the company carried out another interesting
effort, which promised at least 10% gain in Coal consumption. This was the
adaptation of a complete “ pre-heater,” system on board the turbine ship
The Lungstom pre-heater was as its name implied, a system of pre-heating
the air supplied to the furnaces to decrease the losses of heat known to
exist from the ordinary “cold air” supply in the ordinary forced draught
After a series of four voyages, it was unfortunately admitted that theory
sometimes has to give way to practice. Perhaps it was the adaptation to
existing circumstances which defeated the object, for mechanical failings,
little suspected by the designer, developed on board ship to such an
extent that whatever efficiency was gained in theory, was lost in the main
because costs and, more important still, the inability to maintain
scheduled times of ships arrival in port, condemned the pre-heater in the
eyes of a company concerned in the “time factor.” The expression “time
factor” may be again applied in the History of Coal, for in this period of
progress, of experiment and data, was the ever-present advance of the “Oil
Engine”. Figures of cost were a direct connection between the cost of Coal
and its efficiency against the cost of Oil and its greater efficiency,
thermal units on the one hand being a maximum of 14,500 against the finer
Oils up to 19,500.
In the early 20`s one might say that the average price of Coal against Oil
was about one-third, but to keep a balance of efficiency on the “cost2 per
ton rule basis, the cheaper one could buy Coal the better for all
concerned in Coal burning ships.
These cheaper Coals were either of a high % low volatile type, or the high
ash content type. In the first, one could quote the most famous (or
infamous to some engineers) Polish Coal delivered on board at Gdynia, many
years ago. This Coal needed special treatment and it was only with all the
previous knowledge gathered that one could immediately advise engineers to
shorten fire-bars by the building of an extra fire bridge either in
conjunction with or separate from the existing one creating a secondary
air supply and thus completing combustion within the fire- box and tubes –
rather than up the funnel, which was certainly the experience of the
ignorant. Coals in this category were bought in other parts of the world –
Fushun from North China, Keelung from Formosa, Bakit Assim from Java – all
good efficient, low ash % Coals, if you knew how to burn them, and costing
All Coal has its own peculiarity of burning, coupled with its B. The Unit
value, and we think it can be truly claimed that Blue Funnel engineers
faced up to the use of the higher qualities of Coal of the South Wales
type, the best Scotch previously quoted and some of the American Coals
obtained at Newport News, Pocahontas, Panther, & Freburn, New River ( in a
conveyor system of about 800 tons per hour loading time ) all of an ash %
about 10 down to the lower grades where ash content rose as high as 20%
with consequent choking and continual cleaning of fires, nest of fine Coal
dust on tube ends and consequent loss of boiler efficiency. There was,
too, Coal of fusible ash content that brought down fire bars whatever the
care of control and supply; Coal, where high air pressure had to be used
for steam, and the ash fused to a solid lump within four hours` duration
of cleaning routine.
Oh, yes! We could use Coal in the Blue funnel line, but we knew we were
fighting a losing battle with Oil.
So much can be said for Oil – but what of success in the use of Coal? Let
us quote the figures of the last user, the DIOMED.
Her highest efficiency was 117.8 % which seems to prove that the efficient
engineer can ever beat theory – in practical experience.
As an example of how the quality of Coal deteriorated, or the knowledge as
to how it should be burned, the efficiency on the last voyage of the
DIOMED had dropped to the very low level of 46.1 %.
Coal called for very careful measurement in bunkers, to ensure the correct
amount of Coal remaining at the end of a passage; constant supervision was
necessary when bunkers were being taken to ensure that the Suppliers
trimmers would trim the Coal correctly. Constant observations were
necessary to be satisfied that a fire in the Coal bunkers had not started
– some Coals were more liable to this hazard than others – and in addition
to those difficulties, the ventilating fan and air trunks had to be
examined and kept Clean to prevent them going on fire. This did happen on
a number of occasions on board different vessels.
Transcript of Article by Lawrence Holt, A. G.
Arnold and A. V. Harris.
Published in “ The Marine Engineer & Navel
Many thanks to Mr Gerry Weatherhead, for this
very interesting article.