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International Engineering Congress (1901 : Glasgow.

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formation and labours of such societies as those constituting this
Congress.



Co-!. John Scott, Professor Capper, and Professor Biles took
part in the Discussion.

On the motion of the Chairman a vote of thanks was accorded
to the author.



'APPROXIMATE RULES FOR THE DETERMINATION
OF THE DISPLACEMENT AND DIMENSIONS OF
A SHIP IN ACCORDANCE WITH A GIVEN PRO-
GRAMME OF REQUIREMENTS.''

Paper by J. A. NORMAND.



Abstract.

THE problem which forms the subject of this paper is the one
most frequently proposed to the naval architect, but, although
much has been written on the subject, no simple method of solving
this problem has hitherto been shown.

The proposed method is, like the more complicated ones already
in use, based upon the equation of displacement.

When the plans for a new vessel are to be laid down, the surest
and simplest process is to take as a type one or more vessels
differing as little as possible from the one to be designed pre-
ferably an existing vessel, of which all the data, partial weights,
and results are well known, so that the calculations may be based
on facts and not on hypotheses and to work out the changes
required by the slight differences between the programmes of the
old and the new ship. The possible errors are limited in that
case to those that may be committed on slight differences.

If the vessel to be designed is a cargo or passenger boat, or a
yacht, -size generally forms part of the programme. Not so in
a war vessel, where size and displacement must, in most cases,
be reduced to a minimum. This paper deals especially with war
vessels, although the proposed rules may be used with great
advantage for all kinds of ships.

If the speed is not altered, but only weights added or suppressed,
the author investigates what the displacement of the new ship
will be, supposing her to be exactly similar to, and differing only
by scale from, the one chosen as type, the water-line remaining
at the same relative height in order that the fineness of the lines
be not altered. The following simple relation between the weights
first added to the vessel chosen as type, and the ultimate increase
of displacement, is arrived at, viz. : -

The plus or minus difference of displacement must be equal to
the plus or minus difference of weights, as calculated for the vessel
chosen as type, multiplied by a co-efficient k, which can be exactly
determined, and is nearly constant for all classes of vessels, its



150 DISPLACEMENT AND DIMENSIONS OF A SHIP.

mean value being about 3.60 for the general conditions of the
programme to be fulfilled.

Knowing by this very simple rule the approximate displacement
of the ship to be designed, it is easy to calculate the dimensions,
horse power, weights of hull, machinery, coals, etc., by reference to
the same elements in the type vessel.

The author then gives instances of the application of these
rules. Taking as type a cruiser of the " Diadem " class, of which
all particulars are obtainable, such problems as the following are
considered in detail, viz. :

What would be the displacement and dimensions of a similar
vessel

(1) If small tube boilers were substituted for Bellevilles, sup-
posing the speed, steaming distance, thickness and distribution of
armour, weight of guns and ammunition, etc., to remain the same?

(2) If cylindrical boilers were substituted for Bellevilles, the
other conditions, as above, remaining the same?

(3) If small tube boilers were substituted for Bellevilles, the
weight of guns, etc., reduced by 35 tons, the weight of armour
reduced by 20 tons, and the steaming distance increased by 30 per
cent., while the speed remained the same ?

The few problems which were solved by the new method are
sufficient to show how easily it may be applied. It elucidates
very simply a question which most people, and even some naval
architects, do not clearly realise -the extreme importance of light-
ness in a war vessel. The immense advantages resulting from a
reduction in the weights of war vessels will certainly lead, sooner
or later, to the adoption, 'not of small water-tube boilers, but of
mean water-tube ones of some type or other, capable of standing
a high rate of combustion.- Even this substitution will not be
sufficient if the race for speed continues. Steel of high tensile
strength will be needed for the hulls of large vessels; but the
greater part of the advantages to be derived from its use will
be lost until equally strong steel, not hardening when rivetted hot,
can be produced commercially and with certainty.



M. Emile Bertin, Mr. James Hamilton, Mr. R. T. Napier, and
Professor J. H. Biles took part in the Discussion.

On the motion of the Chairman a vote of thanks was accorded
to the author.



"THE HYDRAULICS OF THE RESISTANCE OF SHIPS."
Paper by E. C. THRUPP.



Abstract.

THIS paper investigates a phenomenon in the laws of motion of
water which may be briefly stated as a divergence from the laws
of stream line motion enunciated by Poiseuille, Osborne Reynolds,
and others, when the dimensions of the channels give hydraulic
radii exceeding two inches.

It is well known that the friction of water moving in small pipes
at low velocities is approximately proportioned to the velocity, and
that at a certain " critical velocity " the law changes, and the friction
varies as V 3 or V*, and at still higher velocities it settles down to
V 2 or V 1 ' 85

Osborne Reynolds enunciated the " law " that the critical velocity-
varied in simple inverse proportion to the hydraulic radius.

The author has found, by experiments on channels of various
sizes up to about 8 feet in hydraulic radius, that for radii of 2 inches
and upwards the critical velocity increases with the hydraulic radius,
and he finds numerous indications of the phenomenon in published
records of hydraulic experiments, notably in those of the Mississippi
River Commission, carried out at Carrollton, in water about 60
feet deep.

Confirmation of the author's conclusions is afforded by a study
of the nature of channel beds, and the scouring power and silt-
carrying capacity of water flowing at various depths. The depths
and velocities which occur in channels where the beds are
accumulating very fine silt agree closely with the critical velocity
conditions arrived at from surface slope and velocity measurements.
The scour is, therefore, clearly due to the change from stream
line to sinuous motion.

Mathematical theories as to the velocity required to move solid
particles in water have entirely failed to agree with observed facts
in large channels, for there are innumerable instances where the
velocities (at the bottom of the channels) are sufficient, according
to ordinary text book theories, to roll along large cubical boulders,
whereas, in fact, they hardly disturb fine silt or sand.

The problem of the resistance of ships is intimately connected
with this critical point phenomenon, and also with certain wave



152 THE HYDRAULICS OF THE RESISTANCE OF SHIPS.

motions, which the author has also found experimentally to differ
from the accounts given by some eminent writers.

It is generally accepted that the experimental model system of
estimating a ship's resistance according to Froude's method, based
on Newton's principles of " similar motions," is the best system
known ; but even that method requires some " doctoring " to make
it fit in with the results of actual trials. The discrepancies are
due, in the author's opinion, to the fact that the motions of the
water past the model and past the ship at the so-called " correspond-
ing speeds " are not precisely similar motions, owing to the critical
velocity law which rules the motions within the limits of speed at
which such trials are usually made.

The custom of calculating all the known sources of resistance
on some definite basis, and of calling all the rest " wave-making
resistance," is condemned, and the author contends that the
assumptions usually made in estimating the " skin friction " of ships
are not warranted by ascertained facts in other departments by
hydraulic science. For instance, it can be shown that the friction
per square foot of wetted surface in a pipe or open channel depends
not only upon the velocity of the water, but upon the dimensions
of the channel, and the nature of the motion.

To attribute all the obscure features of ship resistance to " wave
action " is misleading, as the production of waves may be only an
effect, and not the cause of the obscurity.

It is true that Froude's experiments with models having various
lengths of parallel body showed great fluctuations in resistance
coincident with the existence or absence of the crest of a transverse
wave near the stern of the model, but the question arises as to
what the position of this wave depends upon. The fact that some
ships have had their performances improved by the insertion of
an extra piece of parallel body, and also the experiments of De
Mas in France on various lengths of canal boats, go to show that
large difference in lengths may make practically no difference in
the resistance.

The author describes some experiments he has made on the
motion of groups of waves resembling the transverse waves which
accompany a ship, and which prove to be quite different from
the laws of motion of groups of waves as held by Lord Kelvin,
Lord Rayieigh, Osborne Reynolds and others; and he dissents
from many of the statements they have made with regard to this
subject, and gives a description of the main features of the currents
and waves produced by the motion of a ship, which are, in his
opinion, more consistent with all the observed facts available for
the formation of a correct theory of the hydraulics of the resistance
of ships.



THE HYDRAULICS OF THE RESISTANCE OF SHIPS. 153

The paper was accompanied by illustrated diagrams representing
the results of the author's experiments, and other matters.



Professor H. S. Hele-Shaw and Mr. J. M. Adam took part in
the Discussion; and the author replied.

On the motion of the Chairman a vote of thanks was accorded
to the author.

The meeting was then adjourned.



12



WEDNESDAY, 4th SEPTEMBER, 19O1.



The Right Hon. the EARL OF GLASGOW, LL.D., G.C.M.G

in the Chair.



" SHIPYARD EQUIPMENT."
Paper by Professor J. H. BILES.



Abstract.

THE necessity for constant improvement in labour-saving tools was
called attention to. The division of the work of a shipyard into
iron and wood work sections was discussed, and further considera-
tion was given only to some iron working tools. The structure of
a ship, and the method of shaping the different parts, were
described. The following machines and tools were described and
illustrations shown: Punching, shearing, countersinking, and
planing machines ; plate-bending rolls and straightening rolls ;
plate-edge planing, beam bending, joggling, and bevelling machines ;
hydraulic punching, shearing, flanging, and riveting machines;
pneumatic tools for riveting and boring, and a few electric driven
tools.

The general subject of the cost of production, and the relation
between the design of structure and the shipyard plant, were
discussed. The general arrangement of plant in a shipyard was
described, and the principal considerations determining the relative
positions of, numbers, and power of different machines were
discussed. The general transportation plant of a shipyard was
described. The illustrations, about eighty in number, were all
lantern slides.



The Discussion was combined with that on the paper by Mr.
Robert Robertson (see p. 158).

The author replied, and on the motion of the Chairman a vote
of thanks was accorded to him.



"ELECTRICAL POWER SUPPLY IN SHIPBUILDING
YARDS AND MARINE ENGINE WORKS."

Paper by ROBERT ROBERTSON, B.Sc.



Abstract.

W T ORKS of this kind, like all others, differ in size, in arrangement,,
and in many other respects so much that each case must be taken
and considered in detail by itself before any reliable conclusion
can be arrived at as to the advantages in that particular instance.

The conditions ruling in a shipyard are so different from those
in an engine works that it will be convenient to consider the two
separately, and also to take the latter part first.

ENGINE WORKS. The advantages claimed for electrical driving
in marine engine works may be conveniently classified under three
heads, viz.: (i) Saving in cost of power; (2) Flexibility of the
system; (3) Increased output.

i. In considering this subject, the saving in cost of power is
too often looked upon as the only advantage to be gained, and the
advantage is treated lightly because the whole cost of power in a
work of this class only bears a very small proportion to the other
costs of production. It must, however, be evident that the
advantages gained under the other heads are such as to result in
substantial increase of output and diminished cost of production,
they are of much greater importance than the saving in cost of
power.

The saving to be effected in the cost of power may be considered
under two heads : (i) The saving in power production; and (2) the
saving in distribution.

By the adoption of a central power plant with boilers and engines
grouped together upon a suitable site, it is possible to use with
advantage all appliances for getting cheap power, and thereby
effect considerable reduction in the amount of steam used per horse
power generated. This saving is placed by several authorities,,
who have investigated the subject, at from 30 to 50 per cent.

In order to appreciate the saving under the head of distribution,
it is necessary to consider the circumstances in each case. Under
the old system of driving, this loss consists of evaporation from
steam pipes, losses in main shafts, belting, bevel gearings, etc. ; and



156 ELECTRICAL POWER SUPPLY IN SHIPBUILDING YARDS.

it is evident that these losses are practically constant at all loads,
and bear a very much higher proportion to the total power when
only partial load is on the plant.

In the case of the electrical system the distribution by means of
wires or cables takes the place of the steam pipes, main shafts,
main belts, bevel gearing, leaving in most cases only short lengths
of straight shafts. The losses in the wires are such that thev fall
off in greater proportion than the load falls off, and therefore bear
a more or less constant proportion to the power being used.

The saving to be effected by this means at full load will probably
not exceed five or ten per cent., but at all other times, when the
load is other than the maximum, the saving will be much greater.

2. Under the second head of the advantages of this system of
power i.e., flexibility little need be said further than indicating
the possibilities.

The use of separate motors for large tools, or for small groups
of tools, enables these to be placed in the most suitable positions for
convenient handling of the materials, irrespective of the position
or direction of line shafts, etc. The advantages to be got by the
extended use of portable tools, more especially in heavy work, is
very great, the time and labour of shifting and setting the tools in
many instances being very much less than if the heavy castings
have themselves to be shifted frequently. The flexibility of the
system is also of great advantage in the extension of works.

3. It is more difficult to appreciate the advantage of increased
output, and it is by no means easy to demonstrate it, but there
has been, on various occasions when the subject has been dis-
cussed, considerable testimony by those who have adopted the
system, that not only a very substantial increase of output is
obtained, but also at a very considerable reduction of cost for
labour. Among other causes for this improvement we have
already seen the advantage of being able to place tools in the most
convenient situations, and the possible large use of portable and
semi-portable tools, several of which may be at work on the same
piece of machinery simultaneously. The absence of a consider-
able amount of belting and shafting also admits of more extended'
and free use of overhead cranes, and such cranes are more speedily
operated themselves by electric power. A further advantage is
obtained from the fact that individual machines can more easily
be driven at their most economical speed by electric driving.

SHIPYARDS. It is evident that all the advantages claimed in the
case of engine works are greatly enhanced when the working of
shipyards is considered. The same principles may be applied as
in the other case, and it is unnecessary to consider them more in
detail; but the advantages to be obtained by the flexibility of the
system reach their maximum in a shipyard as compared with any-



ELECTRICAL POWER SUPPLY IN SHIPBUILDING YARDS. 157

other industry. The tools themselves are, as a rule, of a heavy
class, which can most conveniently and economically be driven by
independent motors, and may thus be disposed in such positions
as to reduce to a minimum the handling of the raw material. With
the increasing size of ships, and corresponding increase of weights
of the component parts, this is of the greatest importance.

Further advantages may be obtained in a shipyard by the facility
with which electricity may be applied to all forms of gantries, cranes,
or other lifting appliances used in the erection of ships. Portable
tools may be applied on board the ships during construction, and
temporary workshops with semi-portable tools fitted up on board.

EQUIPMENT. Here, also, it is only possible to deal with general
principles. Broadly speaking, there are two systems which may
be adopted, viz., the continuous current system, and the multi-phase
alternating current system. As regards the actual driving, either
system is suitable for the shipbuilding industry, and each system
has advantages peculiarly its own; the outstanding advantage in
favour of the continuous current is the fact that motors of this
class can more easily be adapted to run at varying speeds.

On the other hand, there are several advantages with multi-phase
current for work of this class. The starting arrangements are very
simple, especially with small motors ; the moving parts are of strong
mechanical construction, and less liable to damage by overloading;
and there are no brushes and commutators requiring attention.
There is very little between the systems as regards cost and
efficiency.

The question as to whether single motors on each machine tool,
or group driving by means of short shafts should be adopted is of
the greatest importance as regards economy in working. In the
class of works under consideration there is, as a rule, not much
difficulty in arriving at a decision. Unless in the case of special
portable tools, it is not economical to employ motors of less than
five horse power. Below this size the cost of motors per horse
power increases very rapidly and their efficiency decreases very
rapidly, and in addition, where machines are worked intermittently
and at varying powers, it is possible by suitable grouping to arrange
a motor of, say, 10 or 20 horse power upon a shaft to drive
machines which, if supplied by separate motors, would require an
aggregate of more than double that power. Single motors may
be employed in the shipyard to greater advantage, but the tools in
this case are of such a class that in very few cases will smaller
motors than five horse power be required.

It is impossible to consider the question of cost of installation
in a general way, as it will vary in every case according to circum-
stances.

In conclusion, it may be confidently asserted that in the case of



158 ELECTRICAL POWER SUPPLY IN SHIPBUILDING YARDS.

starting new engine shops and shippards. it is undoubtedly the best
policy to adopt electrical power, and that in most cases it will pay
to make the change in existing works.



The Discussion on this paper was combined with that on the
paper by Professor J. H. Biles.

Mr. H. M. Napier and Mr. de Rusett took part in the Discussion.

The author replied, and on the motion of the Chairman a vote
of thanks was accorded to him.




"A MEMORANDUM ON FLOATING DOCKS."
Paper by T. GIBSON BOWLES, M.P.

Abstract.

THE floating dock has developed greatly and rapidly. It has
passed through the same phases as ships; has grown from wood
to iron, and from iron to steel; has increased in size, altered in
form, and been as much improved in design and details as ships
themselves. The older types, such as the old Bermuda Dock,
which is shaped like a capital U, with double sides and bottom,
are even more obsolete than a battle-ship of that date (1868)
would now be; nor could that dock be thought of to-day as an
adequate provision for to-day's warships.

The original floating docks were long iron vessels, with gates at
each end, the whole thing floating on the water. The ship entered
the dock at one end ; the gate was swung to behind her ; she was
shored up inside, and the water inside the dock pumped away from
around her. This was a dock differing from the graving dock
only in that it floated on the water instead of being hollowed out
of the ground.

Then came the lifting dock with open ends, which first sank
in the water, was then pumped out, and raised the ship as it rose.
Its typical form to-day is that of the large and powerful new
Bermuda Dock, which is the type probably best adapted for
general use.

There are also the L-shaped docks, which are of three kinds :
(i) Off-shore docks connected by booms to piles ashore; (2)
Depositing docks with a floating outrigger; (3) Off-shore docks
with a floating outrigger. The two latter are entirely floating,
and wholly free from all connection with the shore.

The floating dock is by no means in an experimental stage. It
has been at work for a century at least, though, like all other
floating structures, it has only in comparatively recent days been
adapted to modern needs. It has been adopted by the most
capable naval authorities, private and public, of all the maritime
nations.

Nor has experience of floating docks brought any decrease of
confidence in them, but the contrary. We find that the British
Government has recently ordered a new and larger one, costing
;i 95,000 delivered on the Tyne, or 2 30,000 in all, delivered

I2A



160 A MEMORANDUM ON FLOATING DOCKS.

ai Bermuda. For it is to be towed to Bermuda to take the place
of the one already there. This dock is self-docking, and is 545
feet over keel blocks, entrance 100 feet, capable of taking vessels
drawing 33 feet, with a lifting power of 15,500 tons. We also
find that the United States Government has recently ordered one
525 feet over blocks, entrance 100 feet, with lifting power up to
18,000 tons, for New Orleans, where these docks have been tried
since 1866.

The floating dock has admittedly the merit of being capable
of use in places where a graving dock would be either impossible
or difficult of construction. But even in a place where either a
graving dock or a floating dock is equally possible, the latter has
very important advantages of its own which do not belong to the
former, as is evidenced by the fact that at many places where
graving docks are not only possible, but are already in existence,
floating docks have been added to them instead of other graving
docks.

The qualities of importance to be considered in a comparison
of docks may be said to be seven in number. They appear to
be:

1. Advantages and disadvantages of the general mechanical

principle employed.

2. Cost, in which is included original cost, cost of up-keep,

and cost of working.

3. Time required for the construction of the dock.

4. Mobility of the dock.

5. Adaptability of the dock for its work under all conditions.

6. Certainty in construction of the dock, both as to time and

cost.

7. Length of time required to berth and safely dock an

ordinary vessel under ordinary circumstances.

Each of the above qualities was then discussed in detail in the
paper.

Finally, to sum up, the floating dock has been adopted, im-
proved, readopted, and continually used by the most capable naval
authorities, public and private, of all the great maritime nations;
it is used, and always successfully, at places where no other kind of
dock can be placed, and at places where there are graving docks
in constant work as well; it is mechanically advantageous over
the graving dock to the extent of requiring only about one-fourth
the latter's horse power to do the same work; it costs but one-third



Online LibraryInternational Engineering Congress (1901 : GlasgowReport of the proceedings and abstracts of the papers read → online text (page 14 of 37)