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18- gun schooner.

The lines are as usual, except that the lower portions of the floors are
cut horizontally leaving a deep keel, probably to prevent leeway. Another
peculiarity is an outside tiller, worked by a block and tackle from a steering
barrel placed athwartship.

593. Whole models with modified "cod's-head and mackerel's
tail " lines. (Scale 1 : 48.) Contributed by John Scott
Russell, F.R.S, 1868. N. 1220-1.

In the early part of the 19th century it was considered that a seaworthy,
comfortable vessel should have a high, wide, and bluff bow, to enable it to
carry sail well forward while yet rising high and dry above the sea. The
bluff bow, however, was found to have a tendency to make a vessel steer
badly. So to counteract this fault the steering was improved by the
adoption of an extremely fine run to the stern, this commencing near where
the bow terminated, the greatest breadth being much nearer the bow than
the middle of the vessel. This fine run was not confined to the lower part
of the vessel, so that a great deal of space was lost and the buoyancy and
stability of the vessel were affected. These two block models show modifica-
tions of this principle obtained by adding a long parallel middle-body.

594. Whole model of a Dutch ''galliot." (Scale 1 : 48.)
Contributed by John Scott Russell, F.R.S., 1868. N. 1222.

Both bow and stern are extremely bluff, and rise a good deal, thus
giving the vessel considerable sheer. Dutch vessels of this form were not
designed for speed, but to be able to safely ride out the storms on the
shallow and dangerous coasts of Holland, while also possessing ample cargo
capacity.

595. Shipbuilders' models. (Scale 1 : 24.) Contributed by
John Scott Russell, F.R.S., 1868. N. 1269-75.

After the dimensions and the general shape of a ship have been determined,

and the " lines " set out on paper, it is usual to construct a model of the hull

to scale, so that its finished appearance can be more clearly realised. The

model is also of the greatest use while building the vessel, as from it the

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178

dimensions of the plates and planks and the best distribution of the butt
joints can be most easily determined. These six examples of yachts or
small vessels illustrate two alternative methods of constructing builders'
models from given lines.

The usual way of making such a model is, to cut from alternate planks
of yellow pine and cedar the horizontal sections or "water-lines" of the
vessel, as set out. on the drawing ; then to glue and dowel these layers
together, and finish by paring off the projecting edges. The difference in
the colours of the wood assist the eye in following the lines, but any
irregularity in figure is still more easily detected by passing the hand along
the curved surfaces. To " fair " the curvature near the bow and at the stern
the lines shown by longitudinal vertical sections, and known as " bow and
buttock lines," are found most convenient; the three whole-block models
here shown have their starboard sides built up of such vertical layers.

In several of these models, however, an entirely different system of
construction has been followed. The transverse sections at various stations
have been cut in thin wood, and these templates have been secured to a
central board at the correct intervals. These frames are then connected by
thin strips of wood, known as "ribbands," which, being placed fairly close
together, indicate the shape of the body.

596. Models illustrating Scott Russell's system of wave-lines.
Contributed by John Scott Russell, F.R.S., 1868.

N. 1216-19.

This series of four diagrammatic models was prepared by Mr. Scott Russell
to illustrate his theory of ship-resistance, and the form of ship that he
advocated and subsequently constructed upon his " wave-line " system.

N. 1216 is a rectangular block representing a floating object, 36 ft. wide,
28 ft. long, and drawing 15 ft. of water. If forced endways, Mr. Russell
considered that the body was ploughing a channel of a sectional area of
540 sq. ft., so displacing 15 tons of water for every foot it advanced.

In N. 1217 the ends of the body have been tapered, so as to leave a flat
bottom with a wedge-like bow and stern, and vertical end posts. There is
no parallel middle body, but Mr. Russell considered that the addition of any
length of parallel middle body only increased the resistance to the extent
that it affected the skin-friction. The curves of the entrance wedge are on
each side two parabolic arcs placed back to back, while those at the after
end are cycloidal; the result gives very fine and hollow bows and rather
fuller sterns.

In N. 1218 the vertical hollow wedge at the bow is maintained, but the
bilges are rounded and, to facilitate the closing in of the water round the
stern, the depth at this part is gradually diminished.

N. 1219 shows Mr. Russell's solid of least resistance, when the mid-ship
section is elliptical ; its form is intended to comply with the following
conditions :

(1) That it shall move the particles of water out of the way just
sufficiently to let the largest section pass and no further.

(2) That the particles of water originally at rest should be at rest after
the solid has passed.

(3) That the force moving the particles shall be constant, and the least
possible.

The solid represented has a length 7 times its greatest breadth, and the
proportion of fore body to after is as 7 : 5. The water-lines in the fore-body
are sine curves, while those in the after body are cycloidal or trochoidal.
Mr. Scott Russell developed several empirical geometrical constructions by
which his ship lines could be easily set out.

597. Whole model of double-ended vessel. (Scale 1 : 48.)
Contributed by John Scott Russell, F.R.S., 1868. N. 1223.

The bow and stern are of equal length, a design that permits the
balancing of the weights in varying circumstances of lading and draught of
water more easily than with an excess of length at one end. Mr. Russell



179

constructed several vessels in this manner, with hollow wave-lines at both
ends of equal length and width (see No. 74). Such hulls were intended for
running in either direction.

598. Robertson's solid of least resistance, and a half block
model of S.S. " Sir John Lawrence." (Scale 1 : 48.) Lent
by Michael Scott, F.R.S., 1876. N. 1429-30.

About 1860 Mr. A. J. Robertson devised this " solid of least resistance,"
in which the entrance and run are concave, the middle body slightly convex,
and the transverse sections circular. From this solid he deduced a form of
ship which he patented in 1861, and his lines were adopted to a considerable
extent in the " Sir John Lawrence," a screw steamship of about the following
dimensions : Length, load water-line, 200 ft. ; beam, 26 ft. ; draught, 11 ft.
Well-rounded bilges were employed as an approach to the semi-circular
sections preferred by Mr. Robertson.

599. Model of a double bulkhead. (Scale 1 : 96.) Presented
by Prof. John Taylor, M.D., 1873. N. 1345.

This form of bulkhead for an iron ship was proposed by Dr. Taylor in
1861. The space within it is to be used as a water- ballast tank, and in this
way can have its soundness readily tested ; it also forms a fireproof bulkhead.
This principle has been embodied in the athwart-ship coalbunkers of
modern merchant and war- vessels and also in the cofferdam bulkheads of
tank steamers.

600. Whole model and lithograph of proposed screw ship.
(Scale 1 : 96.) Lent by A. Thomson, Esq., 1871. N. 1373.

This shows a design by Capt. Archibald Thomson for a screw-propelled
vessel. On each side of the keel, and close to it, is a channel hollowed
out of the floors, both to dimmish rolling and also to secure a water lead to
the screw, which is placed in the dead-wood as far forward as possible to
prevent racing.

A somewhat similar construction, proposed by Mr. Hermann Hirsch, was
adopted in the S.S. " Paouting " (see No. 601).

601. Block model of the " Hirsch " ship. (Scale 1 : 96.) Lent
by Hermann Hirsch, Esq., 1876. N. 1450.

This shows a cargo vessel of the form and lines patented by Mr. Hirsch
in 1872.

The peculiarity consists in swelling out the bilges till they reach the
keel level, thus leaving two channels along the bottom. From the light
water-line to the load water-line the sides flare out, and are then carried up
vertically ; but these features disappear on each side of the middle third of
the length. The objects of these modifications were, to facilitate taking
the ground, to increase the dead weight capacity, and to give greater
stability.

The proposed vessel was to have been of the following dimensions :
Displacement, 8,221 tons ; length, between perps., 450 ft. ; breadth, extreme,
60 ft. ; depth, moulded, 38 ft. ; draught, 20 ft. ; area of midship section,
1,091-3 sq. ft. ; coefficient of fineness, *527; metacentric height, 16 '15 ft.

In 1873 the S.S. " Paouting " was built on this system, by Messrs.
John Elder & Co., to the following dimensions : Displacement, 1,520 tons ;
length, between perps., 210 ft. ; breadth, 33 ft. ; depth, 22-7 ft.; draught,
13-2 ft. On trial, with 800 i.h.p., her speed was 11 knots.

602. Photographs and objects illustrating Froude's method
of determining ship resistances. Lent by W. Froude, M.A.,
F.R.S, 1876. N. 1453.

In 1874, at Chelston Cross near Torquay, the late Mr. Froude com-
menced his investigations on the resistance of ships by the aid of scale
models, drawn through still water at definite velocities, while simultaneously

M 2



180

recording their resistances and trim. He also discovered an important law
that connects the speed and resistances of a model with the corresponding
factors in the actual ship, thus giving the experimental results quantitative
values.

The first four photographs show the means employed in preparing the
scale model, which is cast in wax and afterwards finished by machine and
hand-work to the exact lines of the ship. The other three photographs
show the experimental tank, with the means employed for hauling the model
and registering its indications.

No. 1 shows a series of adjustable templates, each formed of a thin
flexible steel band adjustable by ordinates clamped in a base board ; the depth
of each template corresponds with the distance apart of the water-line
sections, so that the stack of templates gives the appearance of an unfinished
builder's model. One of the actual templates is also shown.

No. 2 shows the moulding box in which the wax model is cast, also the
the core that is inserted in the mould before running in the wax. The box
is 16 ft. long, 2 75 ft. wide, and 22 in. deep ; the mould is prepared in clay
to a series of fixed cross -sections obtained from No. 1 model. The core
is built up on a similar series of sections secured to a base ; these are
partially planked with laths, then covered with calico and coated with
plaster of paris.

Nos. 3 and 4 are views of the machine in which the cast model is cut to
correct water-lines. The model is fixed, bottom upwards, to a travelling
table resembling that of a planing machine ; above the table stretches a
framework which carries two revolving cutters rotating on vertical axes, the
distance apart of which is automatically controlled, as the table travels, by a
template fixed at the side of the machine, and clearly visible in No. 3. The
arrangement is a form of profiling machine controlled by the templates
previously set to the lines of the drawing. The terraced model thus shaped
is finally finished by hand, with spoke-shaves and scrapers, in about three
hours. A short length of a paraffin- wax model is also shown, one side being
as left by the profiling cutters and the other finished.

No. 5 shows the hauling drum, for winding in the steel wire by which
the model is pulled. The engine by which this work is done runs from
150 to 350 revs, per minute under the control of a delicate governor, and
the speed of the truck can be varied from 63 to 120 ft. per minute.

Nos. 6 and 7 show the dynamometric truck, from which the model
is suspended, and by which its movement is controlled. The truck has four
wheels running on rails supported above the tank, and the various recording
drums and pencils are arranged above the truck at a convenient height.

Owing to the ease with which models can be constructed and tried,
Mr. Froude's system has proved of great value in determining the influence of
various proposed alterations in the shape of vessels, and also in estimating the
suitabilities of untried designs. Since 1885 similar work has been carried on
at the Admiralty tank at Haslar, near Portsmouth, by Mr. B. E. Froude.

603. Diagrams of typical merchant ships. (Scale 1 : 48.)
Made by the Admiralty, 1887. N. 1783.

These seven diagrams give longitudinal elevations of two and three-
decked, well, raised quarter, awning, spar, anchor, and shelter- decked vessels.
The position of the machinery and the cargo spaces, etc., are indicated a.nd
the general conditions necessary for classification at Lloyd's are enumerated.

604. Whole models showing bulkhead arrangements. (Scale
1 : 64.) Made by the Admiralty, 1887. N. 1794-5.

These are intended to show experimentally the efficiency of properly
constructed and arranged compartments, and the absolute danger of certain
other distributions of watertight bulkheads. Glass decks and local filling-
plugs are provided so that the behaviour of the vessels, when floating under
various conditions, may be readily observed. For the diagrams illustrating
these cases, see No. 605.



181

605. Diagrams showing bulkhead arrangements. (Scale
1 : 48.) Made by the Admiralty, 1887. N. 1781-2.

Six of these diagrams show a vessel efficiently subdivided by water-
tight bulkheads and flooded in various compartments, both with and
without a watertight main deck.

Three diagrams show a similar ship inefficiently subdivided and flooded
in the bow compartment ; the effect on its stability is greater than it would
have been if no bulkheads had been introduced. The models illustrating
these points are shown in No. 604.

606. Experimental model of water-balance chambers. Lent
by the Admiralty, 1885. N. 1688.

These illustrate the effects of an athwartship compartment, partially
filled with water, in moderating the rolling of a vessel. Such " water
balance " chambers increase the period of roll and lessen the mean angle,
so being specially adapted to vessels of considerable natural stability, which
in a sea-way have a deep quick roll. They were fitted to most of the
battleships of the central citadel type built between 1877-87, but in later
vessels deep external bilge keels have been used instead, the space occupied
by the chambers and the presence of the loose water being serious
objections to the arrangement, while the efficiency of the deep keels has
been surprisingly high.

The chamber consists of a closed rectangular tank extending from side
to side of the vessel and arranged above the protective deck. In the
experiments on H.M.S. " Edinburgh " it was found that 100 tons of balance
water reduced the rolling by 30 to 40 per cent, at angles below 10 deg., but
that the action diminished with increased roll.

607. "Plating" model of S.S. " Mauretania." (Scale 1:48.)
Lent by Messrs. Swan, Hunter and Wigham-Richardson,
Ltd., 1908. N. 2474.

An important detail in the production of a steel vessel is the ordering
of material. To expedite this process as regards the shell or outer plating
of the vessel a half -block model is made as soon as the drawings of a new
design are available. Such a model should give a correct representation, to
scale, of the external form of the hull, and upon it are arranged and drawn
the edges, butts, and other details of the plating with sufficient accuracy to
ensure the actual dimensions of each plate being obtainable.

The model here shown was prepared and used by Messrs. Swan, Hunter
and Wigham-Richardson for ordering the shell plating required in the
construction of the turbine steamer " Mauretania " built by them at
Wallsend-on-Tyne in 1907 for the Cunard Steamship Co. Besides the general
arrangement of plate edges and butts there are here indicated the
thickness of each plate, width of seams, details of riveting and extent of
local " doubling " in the way of coal and entrance ports, ash-doors, etc. The
position and character of the transverse framing of the ship are also
shown as well as the various decks, watertight bulkheads, and special
" liners."

Length, over all, 790 ft. ; breadth, moulded, 87 ft. ; depth, moulded,
60-5 ft.; gross register tonnage, 31,940 tons; indicated horse-power,
70,000 ; speed, 25 knots.

Among the earliest examples of similar models shown in this collection
are those prepared, about 1853, for the inner and outer skin-plating of the
" Great Eastern."



182



SHIP CONSTRUCTION.

The simplest form of water-borne vehicle is the raft con-
structed of logs or brushwood connected into a platform capable
of carrying heavy loads on inland streams. This was supple-
mented by the hollowed or "dug-out" canoe made from a
single log, and by canoes formed of bark or skins secured to
internal frames, thus leading to the built-up boats in which
layers of wood were stitched together and also tied to internal
ribs or frames.

The introduction of decked boats and ships is also of
unknown antiquity, but it is certain that the ancient Egyptians,
Phoenicians, Greeks and Romans used ships capable of carrying
heavy merchandise or large bodies of troops, and that these
vessels had wooden keels, frames, beams and decks, with shell
planking secured by wooden and metal fastenings ; they were
also fitted with arrangements for rowing, sailing, steering, and
anchoring.

Wooden Ships. The structural details of wood-built vessels
are clearly illustrated in numerous sectional models in the
collection, while the changes in outward form are seen in the
fully-rigged models and the various paintings, prints, etc.

Two of the earliest builders to break away from long esta-
blished usage and to produce vessels of greater size and speed
were the Petts, father and son, who built respectively the
"Prince Royal" (1610) and the "Sovereign of the Seas"
(1637) ; they reduced the heavy top-hamper and gave an
improved under- water form to their vessels. Subsequently the
following improvements in ship construction were introduced :
About 1640, a systematic arrangement of pillars, or vertical
supports, from keel to upper deck, was adopted, thus greatly
strengthening the body. In 1710 a considerable gain in
structural strength and durability was effected by the intro-
duction of " cross- timbers " connecting the lower portions of
opposite frames, also a stout wood keelson and transverse
" riders " above the floors, together with limber boards to facili-
tate the drainage of the bottom ; copper sheathing was first used
in 1761, but as it was found to cause oxidization of the iron
bolts, this led to the introduction in 1783 of "metal" for the
under-water fastening. .

In 1796 a number of small frigates were built by Sir Samuel
Bentham with transverse bulkheads which demonstrated the
structural value of the arrangement.

With the additional strains, consequent on increased length
and heavier armament, came the difficulty of preventing the
various portions of a wood-built ship from " working." Diagonal
wooden riders and trusses w r ith large wooden knees were adopted ,
fora time, but the great weight of timber, together with the loss
of internal capacity entailed by their use were serious disad-
vantages, so that from 1827 the use of iron-plate riders and



183

forged iron knees was gradually introduced, and finally became
general in large wood-built vessels.

Sir Robert Seppings in 1806-11 introduced "fillings" of
solid timber between the transverse frames at the lower part
of the ship, and a continuous " shelf " piece and thick " water-
way " at the beam ends ; these structural improvements,
combined with his system of diagonal trussing and bracing of
the frame-timbers, did much to resist the severe "hogging"
stresses to which a vessel is liable at sea. Shortly afterwards
he displaced the heavy "beak" head and square stern by
a rounded form of bow and stern, which gave greater strength
to the extremities and more efficient gun fire. He likewise
simplified the conversion of timber by a method of scarfing and
by the fitting of square heels and a coak in place of chocked
butts to the timbers of a frame.

Many details of improvements in wood construction, proposed
1806-1855, by Messrs. J. S. Tucker, and R. F. S. Blake of
H.M. Dockyards, are shown by a number of contemporary
models.

Composite Ships. After the general adoption of iron ships
they showed certain defects that were not found in those built
of wood, so with the object of combining the merits of both
materials, the " composite " construction was introduced. The
greater resistance of a wooden bottom to penetration in case of
grounding, and the better facilities it offered for the attachment
of an anti-fouling sheathing, led to many attempts towards
combining such advantages with the superior strength and
lightness of iron framing. Sectional models in the collection
show various methods of arranging the outer skin planking and
the inner longitudinal and diagonal ties so as to give increased
rigidity to the composite structure. In 1867, Lloyd's Com-
mittee published Rules and Regulations for the building of
composite vessels, and the twenty original drawings prepared to
illustrate the most efficient arrangements are exhibited in this
section. The composite system has been successfully employed
in the construction of sailing vessels and small steamers in the
mercantile marine, as well as in the smaller types of warship,
but the loosening of bolts and the lack of rigidity has prevented
its adoption for large vessels with powerful machinery. When
the advantages of a wooden bottom are required in a ship of high
engine power the hull is now generally built completely of iron
or steel and then sheathed with wood externally.

Iron and Steel. The superiority of iron over wood for ship-
building purposes was demonstrated by the experimental vessels
constructed by J. Laird of Birkenhead (1829-35), and by the
experiences of the " Great Britain " (1843), while the demand
for a structure capable of carrying heavy armour and powerful
engines resulted in the building of H.M.S. " Warrior " in
1859-61 as an armoured, iron-built, sea-going man-of-war. The
methods of framing iron and steel vessels may be arranged into



184

three systems in the order of their introduction (a) transverse ;
(b) longitudinal ; (c) bracket.

The transverse system carries out the old principles of wood
construction, by using closely spaced ribs crossing the keel and
held together by longitudinal ties. It was adopted in all the
earlier iron vessels, but was very frequently associated with
wooden keels, keelsons, topsides, etc. The advantages of the
system arise from the simplicity and rapidity with which it can
be carried out, the result being that the majority of the largest
merchant steamers are so built, unless a cellular bottom is
considered necessary.

The longitudinal system consisted in the use of a large
number of deep girders, extending fore and aft, combined with
widely spaced complete and partial bulkheads. This arrange-
ment left large areas of bottom plating unsupported, but in
many respects was well adapted to vessels of great length.
The "" Great Eastern" (1858), designed by J. Scott Russell, was
the finest example of this method of construction, but a number
of smaller merchant vessels were afterwards similarly built.
Since 1908 the longitudinal principle has been successfully
embodied in the "Isherwood" construction of "tank" and
ordinary cargo steamers.

The bracket system, first introduced by Sir E. J. Reed in
the building of H.M.S. " Bellerophon " (1865), is a combination
of the two former systems. The deep continuous longitudinals
are retained, but at wider intervals, with short intermediate
transverse frames or "brackets" spaced at about 4 ft. apart.
These divide the lower portion of the ship into many small
compartments or cells, and with the addition of a watertight
inner bottom this combination became known as the " cellular "
bottom. The economy and strength of the cellular construction
had already been shown in the Britannia and Conway tubular
bridges, but when incorporated into a vessel's structure it
afforded exceptional facilities for carrying water ballast, and



Online LibraryScience Museum (Great Britain)Catalogue of the naval and marine engineering collection in the ... museum .. → online text (page 25 of 58)