ARCHIEF
See note inside cover
Lab.
y.
Scheepsbouwkunde
Technische Hogeschool
Ship Report 140
DeIft
April 1970
National
Physical
Laboratory
Ship Division
SHIPS OF TOMORROW:
SOME POSSIBILITIES AND
PROSPECTS.
by A Silverl.af
This
report
is
areprint
of
the
38tb Andrew
Laing
Lecture
delivered
to
the North-East Coast Institution
of Engineers and Shipbuilders
on
Introduction
During his lifetime Andrew Laing saw many striking
changes in marine engineering and himself made significant
contributions towards them. Since 1931, when he died, there have been even more remarkable and dramatic
changes in ships themselves and in the ways in which they
are designed, constructed, and operated. Many technical papers, including several recent lectures in this series
commemorating the life and work of Andrew Laing, have
described these developments in detail: in this, the
thirty-eighth such lecture, I shall try to summarise some of them
and make a few suggestions about future technological possibilities and prospects. Today we are a quarter of a century from the end of a major war which severely
crippled the existing merchant and naval fleets of the world,
but also stimulated immense technical, economic, and social changes. This is then perhaps a good moment at
which to attempt to look forward so that we may be better
prepared to meet the challenges which the next decades
will undoubtedly bringprovided, of course, that the
world is not again disrupted by a devastating war. Cer-tainly for all of us who are in any way concerned with ships these are exciting times; Andrew Laing would have
enjoyed them. The Recent Past
Size and Composition of the Merchant Fleet
A brief look back over the recent past is a useful, perhaps
almost an essential preliminary before speculating about ships of tomorrow. Indeed, a proper appreciation and understanding of such background information may enable us to anticipate future trends and developments, and not to be taken so much by surprise, as many of us have been, by some of the events of the past few years. During the past quarter-century there have been many striking changes in the size and composition of the
mer-chant and naval fleets of the world, and in the nature, size and speeds of the ships which form their largest and most
important groups. A continuous and unprecedented
technical development in almost every type of conventional ship has been matched by spectacular innovations in highspeed marine craft, of which the most dramatic has
prob-ably been the hovercraft, or waterborne air cushion
vehicle, and by the introduction of a wide range of novel marine vehicles, of which the large off-shore oil drilling
rig has been the most impressive, if not the most beautiful.
These changes can be illustrated in many ways. Just 20
years ago war-time shipping losses had been replaced and
the total active world fleet, excluding the U.S. reserve merchant fleet, had overtaken its total pre-war size of about 70 million tons gross (or about 100 million tons deadweight). In the next 15 years the active world fleet doubled in size, and by the end of 1965 totalled about 160 million tons gross (or about 250 million tons dwt.).
THE 38th ANDREW LAING LECTURE 1969
Ships of Tomorrow:
Some Possibilities and Prospects
by A. SILVERLEAF, B.Sc.
Deputy Director, National Physical Laboratory
8th December, 1969
Its growth rate then of almost 7 per cent per year has continued, is continuing, and will probably continue for some time to come; by the end of next year the world
merchant fleet will exceed 220 million tons gross, or almost
350 million tons dwt. Thus, in about 20 years the world
merchant fleet will have more than tripled in total capacity. Indeed, the ships built within the last five years exceed in
total capacity the whole of the pre-war world merchant fleet. Technical innovations which have led to greater
deadweight in a given size of ship, to higher ship speeds and
to faster turn rounds, have further increased the effective
work capacity of the world merchant fleet, so that it is now
probably almost five times as great as at the beginning of the last war. Some of these changes are illustrated in
Fig. 1.
Naturally, this great growth in the capacity of the world
merchant fleet has been accompanied by a substantial increase in the value of ships at sea. The approximate total value of the 100 million tons dwt. merchant fleet 30 years ago was then certainly less than £3000 million, while the value as built of the world fleet today is about £15,000 million. This shows that on average the much more technically advanced ship of today has been built
at a unit cost which does not, in real terms, exceed that for
the far less efficient ship of 20 or 30 years ago. Indeed, il allowance is made for the higher average speed of the ships of today, then the unit cost on a basis of price per ton-knot, instead of in terms of cost per ton deadweight has probably declined in real terms. This development
cannot be ignored in considering future technical advances
at sea.
The composition of the world's merchant and naval
fleets has also changed radically during the past 25 years.
The introduction of the nuclear powered submarine, and
the development of long range ballistic missiles launched
under water, has, of course, dramatically affected the major navies of the world; the battleship, still a major
factor during the last war, has all but disappeared, and the aircraft carrier, after a period of intense development into
perhaps the most complex and remarkable ship that man has ever created, may now be coming to the end of its life
span. On the other hand, frigates and smaller, faster, and more complicated craft for coastal forces have increased
in importance.
The merchant fleet has altered in an equally striking way. Thirty years ago tankers accounted for about one-sixth of the total capacity of the world merchant fleet;
now they are more than one-third of a vastly greater fleet,
and the tonnage of those now being built represents more
than half that of all
ships under construction. Bulk carriers, 20 years ago a very small part of the world fleet,have, during the past few years, almost displaced the cargo
tramp of the thirties, and the total capacity of those now
shipbuilding. Again, cargo liners today are much larger
and faster than before; the outstanding example of this is, of course, the container ship which, almost a novelty even five years ago, has grown in size, speed and importance in a breathtaking fashion. Each of the largest container ships
now on order can do the work of up to 10 conventional
modern cargo liners, and within a year or two, when there
will be almost 100 large container ships in service, their
impact will be very significant. The mixed passenger and
cargo liner has already declined substantially in impor-tance and, indeed, the world merchant fleets are now dominated by tankers, bulk carriers, and dry cargo ships
to such an extent that they constitute well over 90 per cent
of total world capacity. All the passenger liners, fishing vessels, tugs and harbour craft, high-speed marine craft, and the multiplicity of other marine vessels, thus now represent a very small proportion of the total world merchant fleet tonnage, even though the technical
prob-iem.s involved in their design, construction, and operation are in many cases at least as complex as those of the giant
tankers, bulk carriers, and container ships. Forecasts of the number and total capacity of the ships in the world
fleet for the next 15 years or so suggest that the dominance
of the three main groups of tankers, bulk carriers and dry
cargo ships will undoubtedly grow.
Another illustration of the way in which the character of the world merchant fleet has changed is in propulsion
machinery. Of the pre-war merchant fleet only one-quarter
were motorships, and of the dominant group of
steam-ships 60 per cent were still coal burners. Thirty years latei
the position is very different. Two-thirds are motorships
and less than 2 per cent of all ships are coal fired; indeed,
it is perhaps surprising to find that almost 3 million tons gross of ships still burn coal. Further, of the 50 million
tons gross of steamships in service in 1939, almost 80 per
cent were driven by reciprocating engines, and less than 10 per cent by steam turbines. Thirty years later the
posi-tion is, of course, radically different. Now of the 75 million
tons of merchant steamships, more than 70 per cent are
powered by steam turbines and little more than 20 per cent are still driven by reciprocating engines. The average power
of propulsion machinery has also increased during the
past decades. While overall figures may be misleading, the
change is reasonably well reflected by comparing the typical pre-war cargo tramp having a reciprocating steam
engine of about 3,000 h.p. with the modern medium-sized cargo liner with powers frequently exceeding 20,000 h.p.,
while the largest container ships have steam turbines
delivering well over 100,000 h.p. Ship Size and Speed
Changes in the size and composition of the merchant fleets of the world have been accompanied by equally striking increases in the sizes of the largest ships of each type, and of the average size of ships of most types. The service speeds of ships have also changed during the past 20 years, probably more than in any previous similar
period. These changes have been more apparent in tankers
and in cargo liners than in practically any other type of
merchant ship. The size of the largest tankers has increased
almost 20-foldfrom about 20,000 to now nearly 400,000
tons deadweightbut the service speed of the faster
tankers has risen only from about 14 knots to less than I 7 knots, and few of the even larger tankers which are being planned today are likely to have service speeds higher than those of present vessels of this class. On the
other hand, while the modern medium-sized cargo liner is
not very much larger than her predecessor the pre-war cargo tramp, she is very much faster. Indeed, many
modern cargo liners of this type, with service speeds well
above 20 knots, are among the fastest merchant ships
afloat on a basis of speed-length ratio, and have hull forms
even finer than those considered suitable for passenger
liners and ferries. The growth in size of container ships has been one of the most remarkable features of the past few years, and now there are at least 20 container ships under construction which have similar dimensions to
Queen Elizabeth 2; with hull forms, speeds, and powers not
dissimilar to those of the largest ocean liners ever built, these container ships thus represent an extraordinary
example of the way in which the marine transport scene is being traiìsformed. Some smaller displacement vessels, as
well as hydrofoil ships and amphibious hovercraft, have
speeds even higher than those so far reached by the fastest
container ships; indeed, it is now possible to travel over
water at more than 50 knots by these three different kinds
of fast marine craft. Such speeds have been reached by both foilcraft and hovercraft with displacementsor more properly, all-up weightsof over 150 tons and there are already realistic plans for very much larger vessels to travel at even higher speeds. Some of these features are
illustrated in Fig. 2.
The average size of most types of ship has also increased more rapidly during the past 25 years than in any previous
comparable period. The recent rate of growth is demon-strated by figures for all the merchant ships built at a particular time. in 1948 almost 450 ships of 1,000 tons gross or above were launched throughout the world,
averaging about 5,300 tons gross, or approximately 6,600
tons dwt.: 10 years later there were almost 1,000 ships
averaging 9,600 tons gross, and last year the world output was 1,100 ships with an average size of 15,000 tons gross,
or about 22,000 tons dwt. While these figures indicate a marked growth in the 'average ship', they also show that the average is not only very much less than the largest
group, but increases much more slowly than the size of the
largest ships. Thus, for tankers the average size of the
largest group in service (taken as comprising 2 per cent of all tankers exceeding 1,000 tons gross) has increased
four-fold during the past 15 years, and for bulk carriers the growth during the past decade has been almost equally rapid; indeed, nearly three-quarters of the total tonnage now on order is for tankers and bulk carriers averaging
200,000 tons dwt. Some of these features are illustrated in Fig. 3. Trawlers are another class of ship which has shown major changes in complexity as well as in average size, but
for other ship types such as passenger liners there has not been the same marked increase in size. Again, for cross channel and other passenger ferries, and for coasters, increase in average size has been due more to greater beam and fullness leading to greater displacement than to
greater length.
Improvements in Per/òrmance
Not only have there been great increases in the size of the
world merchant fleet, and in the sizes and speeds of the ships which form its dominant groups, but the
perform-ance of almost all classes of ship has steadily and
signifi-cantly improved. The shipowner or ship operator judges performance in
terms of his
real targetminimum
operating cost to carry a specified payload at optimum speed over a particular route or stated range. The payload may be either a deadweight cargo, such as oil, a light-weight load of passengers, or a weapons system or other mixed weight and volume load. The range is generally an independent operational variable, but optimum speed, though usually treated as another independent parameter, should more properly be derived from an economic analysis in which payload and range are major factors. However, fashion, sometimes disguised as "keeping up with the competition", often results in ship speeds con-siderably higher than those obtained by such a rational approach. Since total operating costs include both direct cost for fuel, crew and maintenance, and also fixed and indirect costs which depend, among other things, on initial capital expenditure. a really satisfactory
perform-ance criterion should leflect all these factors in an un-ambiguous and acceptable manner. However, such a criterion is difficult, if not impossible to define, and it is necessary to be content with less comprehensive indices
of performance
One such index is an efficiency factor which gives an overall assessment of the hydrodynamic qualities of the hull, including any appendages; another, perhaps more useful to the ship designer, is specific power, which is a measure of the power required to propel a specified
dis-placement at a stated speed, and thus indicates the quality
of hull form and propulsion device combined. Careful examination of the values of hydrodynamic efficiency and of specific power for comparable ships of various
types designed over a period of many years, shows
that steady but significant improvements in performance
have been achieved. Perhaps these can be illustrated most vividly by comparing values for ships recognised as being
outstanding in their time; one such example is a compari-son between the famous Lusitania, completed in 1908, whose sister ship, the Mauretania, held the Blue Riband for so many years, and the Oriana or Canberra, which entered service just over 50 years later. Although these ships were very similar in overall size and displacement the modern liners are slightly shorter, much broader, and
operate at lighter draughts, thus giving the naval architect
a considerably more difficult hydrodynamic task; never-theless, their specific power values are little more than two-thirds those of the earlier vessels. This is illustrated in Fig. 4. There have also been steady improvements in
the efficiency with which marine prime movers and power plants convert the chemical energy of fuel into a mechanical
form in which it is readily utilised to propel a ship. Specific fuel consumption values illustrate this; thus, for steam turbine installations of about 30,000 h.p., a good fuel consumption rate 30 years ago was 0.6 lbs./h.p.-hr.,
while today values close to 0.4 lbs./h.p.-hr. can be
guaran-teed. While such impressive relative reductions have not been achieved for large diesel engines, here also
appreci-able gains have been made. Lower fuel consumption rates
mean lighter bunkers for the same range, and improved power plants and propulsion machinery have also led to substantial reductions in machinery weights. Finally, better structural design methods have helped to reduce the
lightweight of ships of most types, so contributing to the general increase in payload-displacement ratios. The overall effect of all these factors can be expressed in terms of a transport efficiency defined as
Transport Efficiency = Thermal Efficiency x Hydro-dynamic Efficiency x Payload/Displacement Ratio.
The wide range of ship types, and the complex changes in
size, speed and duties for each type, make it extremely difficult to give representative and accurate values to the improvements during the past quarter century in these
efficiencies. However, for most ship types for which fairly direct comparisons can be made over this period, it would not be unreasonable to expect to find increases in thermal efficiency of fully 20 per cent, in hydrodynamic efficiency
of at least 10 per cent, and in payload-displacement ratios, of about 10 per cent. The overall improvement in transport efficiency would thus be about 40 per cent,
and for many ship types may well exceed this.
In the past this steady improvement in performance levels, often taken for granted but which is clearly the result of much intensive research and development, has had a pervasive influence on the development of ships of all types, even though this has not always been openly recognised. The extent, indeed the possibility and
likeli-hood, of further improvements in fuel rates, hydrodynamic
efficiency, and payload ratios, will have some effect on
future developments, though these may not be so great as in the recent past. However, improvements in performance
are not necessarily all expressible in such quantitative
terms. Indeed, it may be that the most significant improve-ments from the point of view of passengers and crew have
been of quite a different kind: thus many would maintain that better shipboard ventilation, particularly air con-ditioning, and higher standards of accommodation and
modern galley equipment, have been more satisfying than any other technological innovations. In the same way, new safety regulations and the introduction of greatly improved navigation equipment and techniques have played a major
role in increasing safety and comfort at sea.
Present Situation
Before attempting to predict, however tentatively, possible
future developments in marine transport, particularly in
the size and speed of conventional ships and the evolution of new types, it is useful to consider sorne of the technical,
economic and operational factors which affect what is
either possible or likely. The ships of today are clearly the
result of an overall assessment for each particular marine transport situation of all these factors, necessarily
inter-related in a complex and often imperfectly understood way. lt is likely that in future these factors and their interactions
will be more clearly identified and studied, and methods will be developed for describing and analysing them in ways which can lead to decisions based on more precise considerations than have been possible in the past. How-ever, the essential elements of experience and judgement
will always be required and, indeed, will probably remain
decisive.
Technical Factors
As well as serving as a measure of achieved performance, a
parameter such as specific power (which is in principle a form of transport efficiency) can also give some useful guidance on likely developments in the size and speed of
ships. It is helpful to relate values ofspecific power, defined in engineering units as horsepower per ton-knot, to a speed coefficient involving only ship speed and displacement and which may be regarded as a form of "volumetric" Froude number. Table i and Figure 5 are based on data for a very
wide range of types of ships and other marine craft, from
the largest slow-speed tankers to small high-speed hover-craft and other unconventional marine vehicles. They show
that in general, as expected, specific power increases
steadily and markedly with speed coefficient. It seems also that for each particular combination of speed and displace-ment there is a minimum specific power corresponding to
the "best" performance yet achieved, and these minimum
values form a continuous curve which brings together on a common basis almost all types of marine craft.
The range of values of minimum specific power is extremely wide; for the largest tankers it is less than 001 horsepower/ton-knot, while for all existing craft which run at above 40 knots it exceeds 1 horsepower/ton-knot even in calm watermore than 100 times as much. The
curve of minimum values suggests that for a given
speed-displacement ratio there is often one type of marine craft
with a significantly better hydrodynamic performance than
others, and gives an estimate of the minimum power
required by such a craft. It also demonstrates the penalties
in power incurred by design constraints or by a decision not to adopt the most favourable type of craft. Fig. 6 illustrates the general guidance which can be directly derived in this way; it shows that the minimum values of power-displacement ratio (horsepower per ton displace-ment or all-up weight) rise steeply with speed but fall
steadily as displacement increases. This is vividly illustrated
by the point made in a recent paper that at speeds above 28 knots less power may be required for a ship of 35,000 tons-displacement than for one of half that displacement. It is clear that there are serious limitations on speed-displacement values which are likely to be achieved in practice. The central lesson is that high speed at sea
demands very high powers, with all that this implies in machinery weight, fuel consumption, and capital and
operating costs.
The concept of specific power is also useful in assessing
the prospects for different types of propulsion plant and propulsion device, and for demonstrating the important
and critical connection between the power-weight charac-teristics of machinery, their specific fuel consumption and
the practical and economic range for a particular type of craft. One general conclusion from this is that craft
operating at high speed-displacement ratios are inherently short range vehicles; thus efficient ocean-going high-speed
ships must in principle be large ones and, indeed, this explains much of the recent development of very large
high-speed container ships. A comparison of performance figures for some container ships having conventional type
bulls with those for unconventional high-speed marine
craft emphasises this point. Table 2 shows that for
medium and large size container ships the transport efficiency measured by specific power, based either on displacement or perhaps more realistically on payload, is at least 20 times higher than that achieved by either an ocean-going sidewall hovercraft similar to that forming
the basis of a current U.S. project study, or a possible large ocean-going hydrofoil ship. lt is difficult to believe that the somewhat greater potential speed of unconventional vessels
can possibly outweigh their serious relative economic
in-efficiency, except possibly for very special applications, and
perhaps the overall implication of these comparisons can be best expressed by adapting an old boxing maxim: "A
big fast 'un will always beat a small fast 'un."
It is perhaps worth saying a word or two more about the
performance of high-speed marine craft since these have not unnaturally excited considerable interest during the past few years. The past decade has seen the introduction
of the hovercraft or modern marine air cushion vehicle, the design and construction of hydrofoil ships with automatic
control systems giving remarkable seakeeping qualities,
and further improvements in high-speed semi-displacement
ships, which now form effective fighting units in many
navies throughout the world. Specific power values in calm
water and in average seas for such craft are illustrated in Fig. 7 and a measure of their ride comfort in realistic sea
conditions is shown in Fig. 8. Figures such as these remind
us that present craft operating at high values of s peed-displacement coefficient have very high specific power requirements, and that their ride characteristics are con-siderably less comfortable than those of most other
transport vehicles, including modern passenger and cargo
liners.
Econo,nic Factors
For almost all ships and marine craft of whatever type the
principal design features are in practice selected for economic reasons rather than technical efficiency alone.
These economic considerations are ultimately reflected in total operating costs which depend increasingly on initial
capital expenditure, so leading owners to press for lower
building costs, and also on design features which can affect
running costs in many different ways. Thus, fuel and maintenance costs are influenced by machinery type and the extent to which automatic and remote controls are
adopted, crew costs by other automation techniques, while
different cargo handling systems can have a significant effect on the nature and cost of shore facilities required and the time for which they are used. Many owners have
stressed recently that the ways in which such factors affect their overall costs are altering significantly, and it is by no
means clear that the same technical factors which in the past have been most important will necessarily be so critical in future. It is just such new overall assessments
which have led to many of the recent remarkable
develop-ments in marine cargo transport systems. The general
conclusion from these assessments has been that for bulk cargoes, whether liquid or solid, and for general cargo which can be carried in containers or their equivalent, the
biggest possible ship is the best.
An equally important economic conclusion from such an overall approach is that high speeds at sea are only
justified for relatively high-value cargoes. However,
perhaps the highest value marine cargo of greatest future significance will be passengers on short business and
holiday journeys or longer pleasure cruises, not all of whom
want to travel at high speed. Cost, comfort and
con-venience appear to matter more to passengers who choose
to travel by sea than speed itself. For this reason very high-speed passenger ships, including unorthodox craft, are unlikely to play more than a minor or peripheral role in the future even though they present some of the most
challengingthough not insuperableproblems to the
designer.On the other hand, recent spectacular increases in the
size and speed of large container ships, the latest of which
will have service speeds above 30 knots, reflect a quite different attitude. Here the ship is not regarded as an isolated element, but as a link in an integrated cargo transport system, often stretching from a point far inland
ofthe loading port to another point far beyond the port of
discharge. This leads to a quite different approach towards the economics of the ship operation itself; direct operating
costs for the ship link in the system may no longer form
the major component, since the cost of container terminals,
the containers themselves and of the overland transport network, may well equal or even exceed that of the ships employed on a particular route. For the tanker trades this approach is also becoming far more important since it is the overall cost of transporting crude oil from the well-head to the refinery, and then of the final product to the consumer, which must be reduced to a minimum, even
though the marine transport link in this system is still often
regarded as an enterprise which must show a nominal profit. Here the capital cost of the land storage facilities
at both loading and discharge points, and possibly even of
the throughput of nearby refineries, cannot be dissociated
from the economic appraisal. Operational Factors
In one form or another operational factors have always been decisive in determining the principal characteristics
of all ships. The shipowner has always asked the designer
to provide him with the best, most suitable and most profitable ship to serve a particular trade route, and the designer has had to work within the limits imposed by technical knowledge and by the economic needs of the time.
Apart from the obvious operational limitations imposed
by dependence on wind in the days of sail, the most important recent limitations of this kind have been those which have affected the size of ships. First, technical factors, particularly the strength of timber, prevented
the construction of large ships, but the use of steel for ship
hulls has almost entirely overcome this long-standing restriction and the growth in the power output of ship
propulsion machinery has now also removed another possible technical barrier. Next, the limitations imposed by port and harbour facilities have been of most signific-ance. On many services draught and length limitations at
or near terminals have imposed severe restrictions on ship size, and while continuous and regular dredging has made
it possible for ever larger ships with greater draught to use many ports, length limitations are not so easily re-moved. Even if berths and locks are extended it is some-times not possible to swing ships of more than a certain length in a port situated on a river, and this has been one
of many factors which has influenced the growth, and later
feature, perhaps the oldest and most fundamental of all,
has become significant ; the depth of the sea itself is already
beginning to determine the largest size of tanker or bulk carrier which can operate Ofl some ocean services. Thus, the depth of water in the English Channel may decide the size of the largest ships which will do no more than approach many of the major ports of northwest Europe. However. even this fundamental factor will not limit the maximum size of ships, but lead instead to a radical re-appraisal of the way in which the largest ships are used.
Cargo will no longer always be carried from port of loading
to port of discharge by a single ship, but off-shore
moor-ings or artificial islands will be used as transhipment points
where large ships meet relatively smaller vessels. The modern barge-carrying cargo liner can be regarded as a special form of ship-to-ship transfer. Of course, there is nothing new in this; the big ships of one generation have frequently become the coasters or even the lighters or
barges of the next. Only the scale and pace have altered. Ships must, of course, be repaired, as every owner well knows. At all times it has been essential to make sure that
docks or other repair facilities have kept pace with the size of ships and their refit and repair needs. There have
been many changes in the nature of repair facilities ; thus
floating docks are not as common as was once expected, nor do they serve the largest ships of today. Again, it is
unlikely that the maximum size ofships will be significantly
affected by the cost of providing adequate dry docks for repair purposes in sufficient numbers throughout the world ; instead it is quite likely that new techniques for repairing ships afloat will be rapidly developed when the
need is clearly apparent.
The general problem of handling ships at sea, including
stopping them in an emergency, is not a new one to the mariner. Clearly it has become more prominent as ship
size and speeds have increased but, here again, techniques
have on the whole kept pace with requirements. There have always been some accidents due to failure to handle a ship safely in extreme conditions, or even occasionally in good conditions, and these will undoubtedly continue,
but it is difficult to visualise such considerations exercising a stranglehold on the development of new types of ship.
Other operational requirements of equal importance to
the shipowner do not necessarily affect ship size directly.
Thus, convenient and efficient shore arrangements to
facilitate the loading and discharge of cargo, or to encour-age passengers by providing easy access routes to the ship,
are an important operational requirement. There has always been a complex relationship between the charac-teristics of the ship and of the shore facilities, and recent studies, such as Ship-Shore 1980, have made it clear that
in future ships will probably be more strongly influenced by. and exercise influence on, port facilities and amenities. Another operational factor which has a considerable effect
on many features of a ship is reliability. Ships have long
established an enviable record for reliability in service and,
indeed, this has been a major factor in the development of almost all types of marine equipment, from the largest prime mover to the smallest but nevertheless critical items, such as navigation aids and cargo handling
appli-ances. However, design is increasingly being influenced by
a more critical appraisal of the reliability of all items of marine equipment, another example of the way in which our growing ability to examine complex systems in an analytical fashion is affecting our whole attitude to ship
operation.
The rapid recent exploitation of offshore oil and other marine resources has led to a whole new series of opera-tional requirements for marine vehicles, many of which have apparently novel features. The development of oil drilling rigs illustrates this well; increasingly ambitious
operational requirements have led, in rapid succession, first
to the introduction of fixed rigs sitting firmly in shallow
water, next to moored and semi-submersible rigs for use in somewhat deeper water, and now to free floating rigs with dynamic self-positioning devices capable of being used in
almost any depth. Associated with these rigs are a wide
range of service vessels, including conventional displace-ment craft, foilcraft, hovercraft, and even helicopters. For
what is in principle the same task, different operational environments have resulted in quite different solutions; what is suitable for the calm waters of a tropical lake or
coastal area near a well-established town is quite unsuited
to the needs of the same waters in remote undeveloped
areas, or to an oilfield in the severe weather conditions of
the North Sea or near the coast of Alaska. There is little doubt that as marine technology grows and we make a more serious effort to find and exploit the vast resources in and below the oceans, so new marine operational
requirements will arise and will be met by novel means. The Future
The merchant ships of tomorrow will be primarily
deter-mined by the needs of world trade, not by what is technic-ally feasible. While the size, speed and other characteristics of future ships will clearly be influenced by what becomes possible this alone will not automatically lead to dramatic
changes. Although advances in science and technology provide the opportunity for future progress they also
impose constraints on what can be achieved at any
particular time. Hydrodynamic specific power
require-ments, minimum structure weight, and the power and fuel consumption characteristics of propulsion machinery, are
important factors of this kind, but they may be altered,
sometimes significantly, by research, particularly if this is
deliberately aimed at a particular target. Novel concepts about the role of ships and other marine vehicles as part of a changing pattern of world transport, and a new
attitude towards the exploitation of the world's resources, may have a greater effect on the shape and size of ships to
come. In this last part of my lecture I shall attempt to examine some of these new concepts and ideas, consider briefly how research may affect our present capabilities,
and hazard some general guesses about the future of ships and their work.
Ships as Transport Vehicles
Until recently ships have been almost exclusively regarded
as marine transport vehicles, and certainly their primary role will continue to be that of carriers of the greater part
of the trade of the world which has to be moved across seas and oceans. However, even in this fundamental task the role of ships has been changing fast. Aircraft have
drastically affected passenger traffic, and their inroads into
the carriage of high-value cargoes are now no longer confined to exotic or low density goods. Equally far reaching has been the relatively new concept that the carriage of goods across water should not be regarded as an objective in itself but more as a link in a continuous transport chain. This view has been a major factor in the recent extraordinary development of the container trade, and it is also beginning to affect tanker and bulk carrier
trades.
The future pattern of world trade will undoubtedly have
a critical effect on such developments. Thus, one recent study expects the world tanker trade, now about 1,000 million tons per year and 25 per cent greater than dry
cargo trade, to continue to grow faster for the next decade
or so, but that afterwards it will grow less rapidly, partly because of the increasing influence of nuclear and other
power sources, so that within less than 50 years world dry
cargo trade will equal if not exceed the tanker trade-each then being almost eight times as great as todaywith only a slightly smaller proportionate increase in the
required capacity of the world fleet. Coupled with this is a
cannot and will not be carried either in containers or in
bulk form will probably account for less than 5 per cent of
total oceanborne trade. If this is so, then the general dry cargo tramp ship will soon be a rarity serving only those trade routes where trade is insufficient to justify a liner service, and container ships will dominate the dry cargo trades. The high-speed container ship will operate ocean shuttle services, and the efficient integration of sea and land transport services at both major, and later subsidiary container ports, will form a transport network which can
have radical effects. One is that total delivery time between
inland points may be reduced sufficiently to neutralise some of the potential inroads of air freight. Another consequence, of which there is already some evidence, is
that the container ship service on its own may not need to
operate at a profit, provided the transport system as a whole does so. This could well lead to even larger and faster ships on major container routes, and there is no
reason to suppose that present service speeds represent the
upper limit. The size of these very fast ships will depend largely on the total volume of trade and on the service frequency which ship operators will feel obliged to offer. I use the description "ship operators" deliberately since it is likely that several services of this kind will be run by
subsidiaries of companies whose main interest will not be
in owning shipsa development ofwhich there are already
striking, if isolated examples.
Not only will tankers and bulk carriers continue to grow
in size but there will be more of them, since, despite the
effects of larger ship size, the number of ships in the world
fleet will also increase. This trend may well pose world-wide port congestion pioblems, unless new methods are developed to speed up the loading and discharge of all types of ships to an extent comparable with that already achieved for container ships, and which is already begin-ning to have a major effect on many present ports; long $tretches of conventional berths in old-established ports
are rapidly becoming obsolete, forlorn and decrepit. If new
container terminals continue to be built, and if discharge methods using offshore buoys and submarine pipelines are developed for bulk carriers, as they are already being applied to the loading and discharge of tankers, then the
character of many of our ports may alter out of all
recognition.While it seems clear that well-established ship types, particularly high-speed cargo liners and large tankers and bulk carriers, will continue to grow in size, number, and importance, the extent to which novel types of ship will affect the marine transport scene is far less obvious. For example, the use of submarines as cargo carriers has been proposed and discussed for many years, but there is still little sign that the technical advantages which they might bring would offset the obvious and serious
opera-tional problems which they would undoubtedly pose. Even
without these operational obstacles any performance advantages are difficult to achieve unless there is an economic case for moving bulk cargoes, generally heavy density ones, at much higher speeds than are common today. Another example of a relatively novel ship type is the twin-hulled vessel, a modern version of the long-established catamaran. The large deck area of the
multi-hulled vessel offers obvious advantages for some forms of
cargo of growing importance, but like so many similar
simple ideas, these are not easy to realise in an environment
as hostile as the open sea. However, there is little doubt that several small catamaran ships will be operating soon on sheltered coastal services, and larger multi-hulled vessels may find limited applications on more exposed routes. Other novel types of ship will undoubtedly be developed to improve the collection, carrying and
distri-bution of cargo; barge-carrying and articulated ships have
already appeared, and there are clear indications that the size of barges, whether carried on board larger ships or
towed or pushed in groups afloat, will increase very much
individual barges of up to 50,000 tons dwt. have already
been proposed.
Finally, it is worth considering briefly whether ships will
continue to play any significant part in the long distance transport of passengers. Except for cruising and other holiday purposes there is little evidence that many new
ocean-going passenger ships will be built, though demand for holidays afloat may well grow and provide a continuing
need for medium size passenger ships. However, even if this does occur it is unlikely to pose many serious design or operational problems since in such ships comfort is more important than high performance efficiency. How-ever, short range marine transport for passengers, as well as cargo, is almost certain to grow in extent, importance,
and in the demands it will make on design and operational
skill and experience. Here two categories can be broadly distinguished: first, those services on which high speed is either essential or desirable to attract traffic, perhaps in
competition with other forms of transport;
second,services in sheltered water or on short sea passages in which comfort is clearly far more important than speed. For high speed services it is probable that relatively un-conventional marine vehicles, such as hovercraft and
foilcraft, will dominate the scene, but where comfort is the
prime consideration ships not very different from those which now serve on such routes will continue to be em-ployed. although innovations may be expected in devices to improve manoeuvrability and to facilitate berthing.
Ships to Exploit the Oceani
Recently ships used as other than marine transport
vehicles have become more important, largely because of our growing need to exploit the marine resources of the
world. Trawlers and other fishing vessels are a long-estab-lished example of this role for ships, and the radical trans-formation in the fishing fleets of the world during the past quarter century well exemplifies the different factors which
bring about change at sea. Three developments in par-ticular have contributed to this; first, the need to exploit previously untapped areas of the seas and oceans, often much further from home ports than in the past; second, the technical innovation of freezing fish at sea, leading to the large freezer trawler and the even larger distant-water fish factory vessel and her attendant fleet of small ships; finally, the introduction of the new technique of fishing over the stern rather than over the side, coupled with the
systematic development of more efficient gear for handling nets and fish, has led to a radical redesign of distant-water
trawlers. Together these three technical, economic, and operational factors have led to a very different look to the
fishing fleets of the world, and there is little doubt that this
process of radical change will continue. The highly
de-veloped countries at least will probably rely more and more
on increased shipboard automation, perhaps with ship-borne digital computers processing data to indicate the probable size, species, course and catchability of fish
shoals. It is also likely that better methods of catching fish
and processing it on board will be developed, perhaps ultimately eliminating all work on exposed decks and allowing fishing to continue in even more severe weather than at present. Already the total world investment in fishing vessels of all sizes may exceed £5,000 million, a figure not small in relation to that invested in larger ships of all kinds, and undoubtedly this capital investment will
grow considerably in the next few years.
The exploitation of the oil and mineral resources below
the seabed and the ocean floor is another major activity involving ships. It has already led to the development of
a wide variety of marine vehicles and structures, from very large oil drilling rigs to small submersibles which can
oper-ate in very deep woper-ater. There is little doubt that marine
on the maritime scene. Many of us believe that it provides
Britain with an opportunity to make a concerted positive contribution to the world of tomorrow in a way which particularly suits this country, and which could well engender a sense of national purpose both satisfying and
challenging.
Ships which serve ships form an important though often
less spectacular part of marine activities. Tugs, barges, pilot vessels, rescue launches and a host of other types of craft have also changed significantly during the recent past and, here again, there is little doubt that new needs will lead to further developments. The technical effort required to meet these essential needs is often under-estimated but it is large, relative to the apparent value of this small sectorofthe marine world, and must not be neglected in assessing how many competent and imagin-ative designers will be needed to bring about further
changes in ships ofall types. Ship Propulsion
Today the naval architect and marine engineer has an
almost bewildering choice of power plants and propulsion devices to meet his needs. Available prime movers include slow, medium, and high-speed diesel engines, gas turbines,
and steam turbines or reciprocating engines supplied by
either conventional or nuclear boilers ; similarly, the
long-established marine screw propeller is far from being the only propulsion device in marine use. Faced with this
diversity, and by a barrage oftechnical and other literature extolling the virtues ofeach system, the designerofeven a relatively conventional ship is often in a difficult situation;
for the designer of an unorthodox advanced marine craft the choice is sometimes more awkward in some respects, though perhaps more restricted in others.
Most ships of the future will undoubtedly continue to be propelled in ways which closely resemble those most frequently used today; the steam turbine and the diesel engine will long dominate the seas, albeit with growing competition from the gas turbine, while the conventional open marine screw, which is both practical and highly efficient, will continue to be used on the great majority of ships. However, other power units and propulsion devices will find more applications; thus, the nuclear reactor, either to raise steam or perhaps later as a more direct source of mechanical power, will doubtless find more merchant ship uses, though these will be crucially dependent on its overall operating economics. Similarly, several types of unconventional propulsion device will find increasing use; some, like ducted, controllable pitch, and contra-rotating propellers, have been in regular
if
limited use for many years; others, like fully cavitating propellers and water jet systems, have undergone con-siderable engineering development in prototype installa-tions; a third group, which includes airblown ram jets and magneto-hydrodynamic devices, are still in the early stages oflaboratory investigation and are, in some cases,
little more than "ideas in principle".
In assessing the prospects for the widespread use of any unconventional marine propulsion system it is essential to recognise that its choice and design must not be considered as a series ofseparate and isolated units, each selected to
have maximum component efficiency, but as an integrated
whole in which the characteristics of main machinery.
propulsion device, shafting or other connections, and needs
for auxiliary power must be closely related. Indeed, such choice must take into account much more than the cost
and performance characteristics of the system, even though
these naturally include fuel consumption and bunker requirements; propulsion systems must increasingly be chosen and designed on a "life cycle" basis in which the costs and difficulty of maintenance over a long period of
service are regarded as important items. Thus, once again,
economic criteria will be dominant. Indeed, in deciding
whether to depart from a well-established but conventional system, the shipowner will be very conscious of the relative
importance of possible improvements in propulsion
com-pared with those which may be obtained in quite different ways, such as by reducing crew costs and turn-round times,
or by increasing the useful payload.
Research and ifs Influence
It is perhaps worth asking what effect research can have, or is likely to have on future ships. Will the ship types of the future evolve naturally without any conscious or deliberate attempt to seek new knowledge and methods which can be applied to ship design, construction, and operation? Or is organised ship research an essential pre-requisite to the development and use of new and better ships? Questions such as these can only be answered if there is a clear recognition of what research is and does,
and an equally clear appreciation of what has already been achieved. First, ship research is not a remote activity con-fined to the laboratory study ofa. few basic disciplines such as hydrodynamics or structural analysis, important though
these may be; it is a very much broader process in which
inter-disciplinary activities, operational research, and
management studies all play a role at least as important as the narrower, technical work related to single disciplines.
The trend to such broad based activities is one that will
continue and which indeed should be encouraged, for it is
only in this way that the full benefit can be derived from
organised research. Whether this country alone can adapt its pattern of support for ship research to recognise these new approaches is another question; here I am solely
concerned with ship research as a general activity, not with
national sponsorship or leadership. In this context it is worth recalling that until recently ship research has been principally identified with ship design and production; largely for this reason shipowners have traditionally considered that shipbuilders and other manufacturers are primarily responsible for supporting research. However, the continuation of such an attitude might well inhibit future progress in developing new and better ships. Ship-owners must inevitably take a greater interest in ship design if only because ship operations are becoming
in-creasingly complex; this should lead them to become more
involved in technical research as weil as in those com-mercial and operational studies which they have long
regarded as their responsibility.
Recognition of what research has and can achieve is perhaps best illustrated by examples. Organised research
in ship hydrodynamics has, of course, long been a respect-able and well supported activity. Its major effects on ship performance can be demonstrated in many ways; one is to
compare the power requirements of comparable ships designed at intervals of 20 or more years apart. Such comparisons will either show that later ships all require significantly less power for the same task or, more often,
that the designer has taken advantage of the improvements
achieved by hydrodynamic research to do a much more
difficult task within the same resources as before. Indeed,
recent research in ship hydrodynamics has had consider-able effects on the proportions and detail shapes of hull
forms. Some of these effects, like the widespread adoption
of bulbous and ram bows during the last few years, have been very noticeable, while others, like the underwater
forms of many present British tankers and cargo liners, are more evident in high performance figures than in outward
appearance. One instance of this is the greater carrying
capacity that can now be obtained without any increase in
principal dimensions or any penalty in power req uire-ments, and there is no sign that further advances of this
kind are impossible. Another example is the recent history
of large bulbous bows for full form ships. Using recently
established techniques it is now possible to make
resistance and to observe and measure the detail flow pattern round a hull form. This work has strongly sug-gested that, contrary to widely held views, ram and bulbous bows may have a more complex effect on ship
resistance than previously suspected, and that the
improve-ments in performance produced by even a pronounced "snout" may be equalled. if not bettered, by simpler hull forms designed on far more rational principles than those
used to justify most present bulbous bows. In consequence
it is quite possible that these startling and often ugly
excrescences may once again become the exception rather
than the rule in tankers. Even more important, this work has shown that significant reductions in power require-ments are still possible for full form ships; thus, research of a basic nature has opened the way to design advances
which can only be realised by further investigations of the same kind.
Hydrodynamic studies can also play an important part
in improving the efficiency of ship operations. They have
already led to ships with far better seakeeping qualities
than before, and to the development of roll stabilisers and other motion control devices. A further and more complex development is the general use of weather routeing services
for ships on ocean voyages, which the meteorological
services of several countries are now beginning to provide.
Such services give advice which helps ships to make the most rapid voyage between ports, taking account of the safety of ship and cargo, and of passenger comfort. Indeed, the avoidance of damage, or at least minimising the risk of damage to ship and cargo, has become an
increasingly important part of ship routeing services, even at the expense of time spent on the voyage. A great deal of information is needed to provide efficient weather routeing
services, perhaps the most important factor being know-ledge of the wave conditions on the route, including accurate methods of forecasting these conditions as far ahead as possible. Knowledge of the effects of sea condi-tions on ship performance is equally important, and, as
yet, incomplete.
Similar considerations apply to research in ship struc-tures. For many years ship structural design has neces-sarily been a semi-empirical process in which hard won experience has been a crucial factor, but there has also been steady pressure to exploit new structural materials and a continuous search for greater structural efficiency without impairing safety. However, whenever there have been radical changes in ship types, or in construction techniques, or when new hazards have been met, the essential background experience has been most lacking.
Thus, periods of intensified research have been associated
with the change from riveting to welding and from
transverse to longitudinal framing, the introduction of swedged plating, the problem of brittle failure in ships, and the use of light alloys and higher tensile strength steels as shipbuilding materials. More recently the rapid growth in the size of tankers and the development of the container ship has emphasised inadequacies in current design methods; thus, transverse strength problems in large tankers make it essential to have better methods of structural analysis, while in container ships, which have exceedingly small deck areas compared with more con-ventional ships, problems of hull torsional strength, and the design of openings, have become important. In the same way catamaran or other multi-hull ships, and other novel types such as barge-carrying ships, high-speed
marine craft and complex offshore structures, pose new structural problems which require research if significant developments are to be possible. We need to know much more about the forces imposed on ships by wave action,
thermal effects, and construction processes, as well as the response of structures to such forces. Sometimes the need
for research of this kind is not fully appreciated, perhaps because ship structures appear to be so efficient already.
While the fact that the shell of an egg is relatively 10 times
thicker than the plating of a large ship is a credit to ship designers, it
does not mean that further research is
unnecessary.
Research into other technical problems also contributes to the development ofbetter ships. Mechanical and marine
engineers will continue striving to improve the
power-weight characteristics of prime movers for ships, to reduce
their fuel consumption rates, to develop more efficient
propulsion devices, to improve the reliability of all marine equipment, and to minimise the noise which they generate.
Instrument and control engineers will devote more effort
to marine systems, including automatic control systems for
main and auxiliary machinery, and to cargo handling appliances, and this will doubtless lead to greater
oper-ational efficiency in many ways. Equipment which requires less shipboard maintenance, even at the expense of carrying
greater shipboard spares and using shore based facilities for much maintenance at present carried out at sea, can make a worthwhile contribution of this kind. Again, ship
operators will be increasingly concerned with the need for
safe navigation as more, larger and faster ships, some carrying dangerous chemical cargoes or with nuclear
machinery, crowd into the world's narrow seas and
estuaries, particularly those round our own coasts. All
these activities require formal research as well as
develop-ment and operational evaluation in rigorous service
conditions.
Research in ship hydrodynamics is not difficult to justify, since ships differ from other engineering structures only in
the crucial respect that they live on the sea and have to survive and move through it in all weathers. Almost all aspects of ship designstructures, machinery and
equip-ment included are affected to some extent by this difficult environment. While ship research in general is not likely to
lead to spectacular sudden advances in ship design or in ship performance, it will undoubtedly result in further quiet and steady improvements in operational efficiency,
safety, and comfort. Without research such improvements
are much less likely, and will certainly take longer. How-ever, because ship research already has so many related but different aspects it
is becoming more and more
necessary for available resources to be used to the best advantage. Britain has long played a leading part in fostering ship research and in applying its results to prac-tical ship design. To meet, and indeed to anticipate future needs it is essential to ensure that such activities continueto be organised and co-ordinated in the best possible way.
In particular the right balance should be kept between the
resources allocated to short-term and to long-terni objectives, and between those devoted to ship design
sub-jects like hydrodynamics and structural analysis, to work leading to improved ship construction techniques, and to investigations aimed at more efficient and profitable
operation. including such diverse topics as better handling
methods and controlled ship routeing. Only in this way can we make sure that technological possibilities are
exploited to the full. An Overall View
It is clear that technological and economic changes during
the past quarter century have already had profound
effects on ships and their work. Shipowners and ship operators will
continue to make ever more difficult
demands on the ship designer for large tankers and bulk carriers, for faster and more efficient cargo liners, and for faster, safer and more comfortable vehicle and passenger ferries. Work already in progress suggests strongly that
new ideas, design methods and devices will be produced to
meet these continuing demands for better and still better ships. It may be useful to attempt to summarise some of these ideas and methods:
ship design and ship operation. Indeed, the whole approach
to ship design is undergoing radical change exemplified
by the extensive techno-economic assessments which now generally precede any decision to order a new ship. These
use analysis methods which increasingly take account of
factors previously neglected, leading to "purpose-designed" ships forming links in a complex transport system instead
of isolated units as so often in the past.
The growing use of computer-aided design methods will have a strong influence on the work of ship designers
and constructors, and will also affect ship operators who are being drawn more closely into technical problems of design.
One consequence of the changing approach to ship operation is the steady evolution of a small number of clearly defined classes of ships dominating the maritime
scene. These dominant types will be tankers, bulk carriers
and dry cargo ships. each evolving steadily to meet
economic needs. There will be more of them and some will
be larger than today's largest, but although their average
size will continue to increase slowly, for many years most
of them will be small ships by the standards of today, if not those oU yesterday. Indeed, they will have shapes, structures, power plants and propulsion devices not very dissimilar to those of their counterparts today.
Another quite contrary, but equally logical effect of new attitudes to marine operations, is the introduction of novel ship types for specialist purposes. The extent to which these will be successful will depend largely on the technical and commercial resources devoted to their
development, but they are unlikely to be more than a minor part of the total world merchant fleet, even though
deep-sea fishing and ocean technology grow in importance.
Throughout the world more effort than ever before
is now being devoted to research and development
activities related to ship design, construction and operation,and this is bound to lead to unexpected innovations and improvements. However, the emphasis in such research activities may well shift during the next decade; while the principal disciplines, such as hydrodynamics and structures, will still require support and will continue to
yield steady advances of practical value, there will also be a growing emphasis on inter-disciplinary activities and on research which is not clearly technological in character.
In general it is difficult to see any technical barriers
to significant developments in ship size, speed, or opera-tional efficiency. The extent to which these advances are
realised will depend very largely on the extent to which we
consider it desirable to support the research and develop-ment necessary to make them possible. This in turn
depends very largely on economic factors.
Acknowledgements
A lecture concerned with such a wide ranging subject as the future of ships must inevitably draw material from many sources. To list a few of the papers, reports and
other references from which I have freely borrowed, might
give a less correct impression than to mention none. and I have chosen this latter course, except in figures based on particular information from specific sources. However, I readily admit my debt to all those on whose work I have leaned, and to colleagues and other friends who willingly and candidly commented on early drafts, and whose help thus eliminated some of my more serious errors. To them in particular I am grateful. Needless to say, any views expressed in this lecture are my own
TABLE i
Typical Values of Specific Power for Ships and Other Marine Craft
TABLE 2
Comparative Efficiency of High Speed Ships and Marine Craft
Notes:
All figures are typical values for type of ship or craft, and are derived from existing examples or detail project
studies.
Fuel and range values are based on overall specific fuel consumption 05 lbs/hp-hr.
Ship Type
Displace-ment A tons Speed V kn Power P hp Speed Coefficient V/All6 Specific Power P/AV
Tanker or Bulk Carrier:
Mammoth 600,000 15 60,000 1-6 <0-01 Large 250,000 15 30,000 19 0-01 Medium 30,000 15 12,000 2-7 0-03 Coaster 4,100 12 2,100 30 0-04 Dry cargo 17,000 17 11,000 3-4 0-04 Container ship 36,000 22 32,000 3-8 0-04 Trawler 1,800 14 2,400 4-0 01
Cargo liner 18.000 21+ 20,000 4-2 O-05
Vehicle ferry 5,000 20 16,000 4-9 0-16 Passenger liner 44,000 29+ 110,000 5-0 0-08 Destroyer 4,000 30 40,000 7-5 0-33 Frigate 1,200 40 48,000 12-3 1-0 Patrol craft 90 50+ 11,000 25 2-5 Foilcraft 70 50 3,500 25 1-0 Sidewall hovercraft 16 32 360 20
07
Amphibious hovercraft 160 65 13,000 28 1 -2 Type Cargo Liner Container A Ships B Amphbious A Hovercraft B Side-wall A Foilcraft B Length L ft 530 700 900 160 220 350 160 240 Weight A or W tons 18,000 36,000 48,000 180 500 4,000 200 1,000 PayloadWp/W -
O-445 050 0-48 0-33 0-38 0-25 0-25 0-20 Wp tons 8,000 18,000 23000 60 190 1,000 50 200 Range R miles 8,500 7,000 5,500 375 550 1,000 400 670 FuelWF/W -
01 0-062 0-1 0-1 0-15 0-22 0-1 O-15 WF tons 1,800 2,200 4,800 18 75 880 20 150 Speed V knots 21+ 22 30 50 60 60 50 50 V/W1/6 4-2 3-8 5-0 21-1 21-3 15-0 20-7 15-8 Power P lip 20,000 32,000 120,000 10,800 36,000 240,000 11,000 50,000Hydrodynamic P/WV hp/ton-kn O-052 o-04 0-083 1-2 1-2 10 11
10
Efficiency WV/P ton-kn/hp 19-4 25 12-5 0-83 0-83 1-0 0-91 1-0
Quasi-Transport P/WpV hp/ton-kn o-116 0-08 0-173 3-65 317 4-0
44
50
400 300 TONNAGE IN MILLIONS o 7937 ¡939
Fig. 1.Total capacity of world merchant fleet. Gross
tonnage values from Lloyd's register statistical tables. Deadweight tonnages are estimated values.
60 5 40 SERVICE SPEED (K HOTS) 30 20 FAST PATROL CRAFT ALL SHIPS
SHIPS > 1000 TONS GROSS
DEADWEIGHT TANKERS GROSS
7950 ¡955 1950 1965 1970
YEAR
T
AMP III S tOUS
/ H OVER CR AFT
FO IL C RA FT
SMALL
NAVAL SHIPS
SMALL CONTAINER SHIPS VEHICLE FERRIES 1 TRAWL ERS DEADWEIGHT GROSS CONTAINER SHIPS PASSENGER LINERS TANKERS RU. K CARRIERS
DRY CARGO SHIPS IO
C CA S T E R S
SMALL CARGO SHIPS
O
IO lOO 1000 ¡0000 100000 loco 000
DISPLACEMENT OR ALL-Up WEIGHT (TONS)
Fig. 2.Typical size and speed ranges.
200
200 150 OEA D WE I GHT TO N N A G E IN THOUSANDS lOO SO AVERAGE FOR LARGEST 2% TANKERS
AVERAGE FOR LARGEST 2/M BULK CARRIERS AVERAGE ALL TANKERS
> 000 TONS GROSS AVERAGE ALL BULK
C4RRIER5
AVERAGE ALL SHIPS > 1000 TONS GROSS O IR 50 P INSTALLED POWER hp) t. DISPLACEMENT Ions) V SPEED (knots) 1960 YE A R
Fig. 3.Approximate average size of ships in service.
STEED COEFFICIENT V/A + IR 70
MINIMA ALL TYPES
Fig. 5.Spec ffic Power Requirements
1950
-
0 01 P O O5 A O IN CALM 0* TE E (lIlI A - DISPLACEMENT (TEE) y - EPPOD (k..I.) 6Fig. 6.Power-Displacement Ratio.
Derived from present minimum values of specfic power for ships and marine craft.
2 3 4 V I I, - DISPLACEMENT (N TONS V - SPEED IN KNOTS P - POWER IN H.P.
Fig. 4.Power requirements for passenger liners.
40 20 30
o SU R FAC E PIERCING FOILS SEMI - DISPLACEMENT CRAFT SUBMERGED FOILS + O
o
AMPHI BIOUS HOVERCRAFTP-TOTAL INSTALLED POWER(hpY w-AL-uP WEIGHT (Ions) : V- SUSTAINED SPEED (knots)
L- TOTAL LIFT : D - TOTAL DRAG - OVERALL PROPULSIVE EFFICIENCY
h - SIGNIFICANT WAVE HEIGHT (litt)
(b) Moderate Sea Conditions
Fig. 7Power Requirements for High Speed Marine Craft.
o
-2
C-3 4 s 6Lt) > IO 4-Fop h/w"3 = O-5(a) calm Water
A M PH I BI OU S HO VER CRA FT -2 3 > Q-O LU W 3 SURFACE PIERCING FOILS L-) Lt-u w a-(2
4<
z O5'
I-'J) -JSENIl -DISPLACEMENT SUBMERGED FOILS
8w
IO I-(-I LU u-O I I LU
X FOILCRAFT SURFACE PIERCING FOILS
+ FOILCRAFT SUBMERGED FOILS
O AMPHIBIOUS HOVERCRAFT (AIR PROPULSION)
4 Ø NON -AMPHIBIOUS HOVERCRAFT
(WATER PROPULSION) ESTIMATED DATA INDICATED BY /
O IO 20 30
40
SPEED COEFFICIENT V/jt16
O IO 20 30 40 50
1000 SO0 3 torI TRUCK cl-.---- GOOD ROAD 0-5 FT5O IN CRIANNEL ISLES BLOCK SPEED 28 KO. o I i I I I I I loo RUS 35 mph. 0BCLA5SROAD 50 O 1500 CC CAR '3 z AVERAGING40MPH FOR u SRN4 IN I HOUR Io o
-
CHANNEL s-5-
SRN6 3O/s SKIRT L) z IN SOLENTBLOCK SPEED 25KO.
O
A
l.0 VISCOUNT AIRCRAFT
o 02 0-4 0-6 0-8 1-0 I-2
VERTICAL ACCELERATION MIDSHIPS (g)
Fig. 8.Measured levels of vertical acceleration for high-speed marine craft and other vehicles.
SOURCES:
Figs.
i and 3.Lloyd's Register Statistical Tables for
Values of Gross Tonnage.
Fig. 4.Bell, T. Speed Trials and Service Performance of the Cunard Turbine Steamer "Lusitania". Transactions I.N.A. 1908, Volume 50, Page 96.
Figs. 5 and 6Silverleaf, A. Prospects for Unconventional
Marine Propulsion Devices. 7th Symposium Naval Hydro-dynamics, ONR, August 1968. (Also N.P.L. Ship Division Report 131, 1969).
