Ships Contruction and Calculation
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SHIP
CONSTRUCTION AND
CALCULATIONS. WITH
NUMEROUS ILLUSTRATIONS AND EXAMPLES.
FOR THE USE OF OFFICERS OF THE MERCANTILE MARINE, SHIP SUPERINTENDENTS, DRAUGHTSMEN, ETC.
BY
GEORGE Member of
Institution
of
Naval
NICOL,
Architects,
Surveyor
Lloyd's Register
to
of Shipping.
GLASGOW:
JAMES BROWN & SON,
52-56
Darnley Street, Pollokshields,
London; SIMPKIN, MARSHALL, HAMILTON, [All Rights Reserved.']
1909.
KENT &
CO.,
LTD.
E.
Preface. advances THEandrapid the
is
details
apology for
placing
of
construction
the
of
ships
steel
the
is
volume before the
present
to
particularly
simple and practical
explain in a
building
the
in
hoped that the matter presented will be found up mentioned that publication has been specially delayed
reference
best
The book
public.
Lloyd's
to
latest
which
rules,
as
so
may
It
include
to
important
certain
in
differ
date.
to
is
be
design
in
writer's
manner some of the proand subsequent management afloat of ships, cargo steamships, and while no claim to special originality is made,
intended
blems met with
it
have been made in recent years both
that
in
respects
from those preceding them, and are "more readily applicable to the changing of construction."
conditions It
hoped the book
is
Marine, ship of
whom
To
the
one,
in
reasons
draughtsmen,
and
mariner
officer
those
that
an of
the
subject
who wish
officer
ships.
may now be
qualify
to
for
the
in
act
as
inspector
or
the
confidence
in
repair
directing
management of his him at any time
his
vessel to
said
to
certificate
be
to
all
essential.
is
compulsory
a
master
of extra
it.
on behalf of his employers of an old one. Or, if sudden damage, calling for immediate temporary to
apprentices,
But besides this, there are other good should know something regarding the construction For instance, it would enable him, if called upon,
examination
why an
theory
vessel
of the Mercantile
officers
shipyard
a more or less intimate knowledge of naval architecture
must pass
and
be found useful by
will
superintendents,
crew
afloat,
the
in
at
the
out
of simple
of
a
were
to
receive
it
of
would give him these.
theory
conditions
satisfactory
new
building
vessel
repairs,
carrying
a knowledge
quickly
arrive
at
his
In
would of
the assist
draught,
mere guess-work or a system of trial and error. In other ways also such knowledge would prove useful. The examples chosen for illustration throughout the book have been selected for their practical interest, and every effort has been exerted to
and
trim
make
the
stability,
unattainable
explanations
by
simple.
In conclusion, the author begs to thank Messrs. Ltd.,
calculations his
J.
L.
Thompson
&
Sons,
Sunderland, for their kind permission to publish diagrams and results of of
vessels
sheets,
and
in
built
Mr. W.
indebtedness to
verifying the
rendered while the
by them
and he also desires to acknowledge Thompson, B.Sc, for help in reading the proof ;
examples, as well as for other valuable assistance
work was passing through the
Glasgow, November,
1909.
press.
•
CONTENTS.
........ CHAPTER
Simple Ship Calculations
CHAPTER
.... ....
II.
Moments, Centre of Gravity, Centre of Buoyancy
CHAPTER Outlines of Construction
.
III.
.
CHAPTER
IV.
Bending Moments, Shearing Forces, Stresses and Strains
CHAPTER
....
CHAPTER
Practical Details
CHAPTER CHAPTER .
.
.
Rolling
.
42
45
75
93 VII. .
.
.177
...
VIII.
197
IX.
Stability of Shits at Large Angles of Inclination
217
.
........ ..... ..... CHAPTER
25
VI.
.
CHAPTER
i
V.
Equilibrium of Floating Bodies, Metacentric Stability
Trim
...
.......
Types of Cargo Steamers
PAGE
I.
X.
254
CHAPTER XL
Loading and Ballasting
.
272
APPENDICES.
Appendix
A
Appendix B
Table of Natural Tangents, of Materials
Appendix C Index
;
Sines
and Cosines;
Rates of Stowage .
Weights .
.......
Additional Questions
297
.
305 309
.
.
324
AND
SHIP CONSTRUCTION
CALCULATIONS. CHAPTER
I.
Simple Ship Calculations.
A
KNOWLEDGE areas
be
of
surfaces
of
only
the
principle
the
indispensable
moments and of how to calculate may perhaps be said to
of
curved
having
boundaries
requisites
with
dealing
in
ship
ordinary
calculations.
In view of first
principle
the
this
we propose
to
spend
a
The
of
area
of
moments, especially as applied a plane surface bounded by
on these
time
little
may be found
taking up areas of surfaces, and afterwards, as
problems.
ship
to
straight
or
unit,
in
English measure,
is
square
usually a
foot,
may
curved lines
be defined as the number of units of surface contained within
The
subjects,
convenient,
boundaries.
its
although
some-
is
it
and sometimes, although more rarely, as a times taken as In France, and on the Continent generally, the metrical square yard. system is employed, the units of surface being the square metre and square These metrical units have many points of advantage, centimetre, respectively. but as the square foot is more familiar to us, we shall make it the standard a
in
square
inch,
our calculations.
The
simplest
figure
whose chief properties are fig.
A BCD
i,
two adjacent be
lines
shown
in
is
sides,
drawn the
a square, such as
through
figure,
which
of
—
all
sides
we
may
obtain
and
equal,
all
the
angles
area
is
right
one side being, say, 6 A B and A D, be divided into 6 equal
the
the
length
points
of
of
division
the square will contain
parallel
to
a
square,
In
angles.
these
If
feet.
parts,
and
sides,
as
36 small squares, each of which
There are, 4 sides equal to a foot, and encloses one unit of area. It is obvious that 36 units in a square having a side of 6 feet. to find the number of units in any square it is only necessary to multiply has
its
therefore,
the length in lineal units
of one side by
itself.
—
In passing to a rectangle the square, being, sides
AND CALCULATIONS.
SHIP CONSTRUCTION
2
i.e.,
the
however, in
length in
a rectangle
of
this
two feet
Area =
we have Fig.
h
and 8
16x8 =
the
for
sides
feet
128
area
are
As an
unequal.
case,
be 16
rule
adjacent
is
same
the
multiplied
example,
let
long respectively.
square
feet.
as
together,
for
a
these
the
adjacent
By
the rule,
SIMPLE SHIP CALCULATIONS.
B
Obviously A
A GB
parallelogram
the
bisects
D,
3
and,
ACBD = ACxBE, AP v triangle ABO equals
as
we have
seen
just
Area Therefore, the area of the of any
area to
know
—
in
25
and a
them, of the
the
rule
Thus, a triangle having
intersect.
of
22
feet,
have an
will
area
of
.
2
and
height
vertical
75 square
The
feet.
may be found by one
lines
this
;
which the other two sides
feet,
By
and it is seen that we only require and the vertical distance between that side
length of one side
and the point a base of 25 x 22
may be obtained
triangle
the
RF
of the foregoing
should be noted that the
it
areas
area of any plane figure
of ship
rules,
straight
by a combination of
or
rules
applied
were of
this
earliest
waterplanes and sections
bounded by
to
the
finding
nature.
ABODE
(fig. 4) Bisect A E be a portion of a ship's waterplane. and through F draw a line perpendicular to A E to intersect the curve in 0, FO will be parallel to A B and DE. Join B and D by straight lines, then and FGDE will be trapezoids. A B, F 0, ED are called ordinates to the curve let these lines be represented by the letters y y.2 and f/ 3 respectively and let h be the common distance between consecutive ordinates. Obtain now the areas of the trapezoids and FGDE by ap-
Let
in
F,
ABCF
:
,
1
;
ABCF
Draw B G
plying the rules already established. G,
parallel to
A
F,
meeting C
then—
B0G=
Area
Using the symbols,
these
BG
x
G
and area A B G F = A
,
may be
Area B 06 = ^^
written
x h, and area
2
Combining we
get
Area A B In the same way area ,-.
whole area A B
F= —
(+ 2y 4
ABDHJ = —{y +
.\ the whole area,
This
AND CALCULATIONS.
curves as
;
x
2y.2
%)
-\-y 5 )
+
a(/ 3
+
2
^432
61
C
*•
1
1
Taking the strength of steel at 30 tons per square inch, this stress allows a factor of safety of rather more than 3-^-, which, in most cases, would be too The form* of section above given low, 5 to 6 being common for ship work. is
by no means the most economical for steel beams. This material admits of many forms, and to show the great importance of distribution
being rolled into
means of increasing the strength of beams against bending, let assume the length, depth, and sectional area, and therefore the weight, to us The only additional work remain as before, but the form to be as in fig. 60. of material as a
*
Within
elastic limits
six its
mild
steel
and wrought iron are equally strong under compression or
by no means true of all materials. Cast iron, for instance, will withstand a wood, on the other hand, has times greater stress under compression than under tension In such cases, for maximum strength on minimum weight, greatest strength under tension.
tension, but this
is
:
Fig.
the section must be ol
but
special
the
design.
may be
The
61.
axis
of
moments must
reduced on the
weaker
still
pass
through the
by concentrating the For example, beams loaded at the middle and material on that side near the neutral axis. supported at the ends, if of cast iron, to be of economical design should^ have cross sections, centre of gravity,
stress
pf such forms as indicated in
fig.
61,
side
—
62
——
AND CALCULATIONS.
SHIP CONSTRUCTION
be done here
to
is
moment
to find the
—
of inertia of the
neutral axis, which, as in the previous case,
the
moment
of inertia in this case
new
at mid-height.
is
section about the
The formula
for
is
/= BH -2bh s
s
12
H
where the
full
depth of beam, h the distance between the flanges, B and b the breadth from the outer edge of the flange to the
the
is
full
breadth,
side of the web.
fig.
60
1728-2 x6x 1000 = n 872
in.
Substituting the values given in
/= nx t-
_•?
i
•
4
12
We
therefore have Stress at top
—-—— —
and bottom of beam —
4*1 tons per square inch,
872
a
maximum stress which is only half of The above is only an illustration
the previous one. ;
various
for
reasons,
girders
of
this
section are not usually rolled with flanges of greater width than 6 to 7 inches.
Taking them at 7 inches, and increasing their thickness to if inches say, with the same weight of material, a girder of 18 inches depth and i T3F inches web could be obtained. The moment of inertia of such a girder would be 1685; and, under the same bending moment of 600 inch-tons, the stress on the upper and lower flanges would be
p =
600 x 9 ~i68T~~
=
tons P er square inch.
3' 2
Let us turn now to the case of a floating ship. We have seen obtain the external bending moment, and to apply the stress formula,
how it
to
only
remains to determine for the material at the transverse section under the maximum bending moment, a method of fixing the position of the neutral axis, and
moment of inertia about that axis. Now, as we know that passes through the centre of gravity of the sectional area, its therefore be easily found. As we shall see presently, the calcula-
of calculating the
the neutral position
axis
may
tion involved
is
conducted simultaneously with that
In setting out
we
to
find
the
moment
are dealing with a built girder,
longitudinal direction
is
to
be
strains.
In ordinary cases the
length
we must
;
moment
for the
moment
we must bear
in
of inertia.
mind
that
and
that only continuous material lying in a considered as available for resisting longitudinal
maximum bending moment
therefore choose
of inertia calculation,
of inertia
as,
the weakest of course,
if
occurs at about mid-
section in this vicinity for the straining were to take place, it
Careful note should be made of the fact that would be at this section. material under tension must be calculated minus the area of the holes for the rivets
joining
the frames to the shell
plating,
the
beams
to
the
deck-plating,
RESISTANCE TO CHANGE OF FORM.
63
This precaution need not be taken with the material in compression, as
etc.
if well fitted, will be as effective to resist this stress as the unpunched Where continuous wood decks are fitted, they are sometimes allowed wood being considered equivalent to about T\ of its sectional area in steel.
the rivet, plate. for,
must be reduced on account of the butts, which strakes, also on account of the bolt holes. For compression the full area is taken. In modern cargo steamers continuous wood decks are seldom fitted, and there are none in the vessel In the case of tension,
are
this
separated by three passing
usually
whose moment of
inertia calculation
given below.
is
As already mentioned, the conditions dealt with in these strength calculations are those depicted in figs. 49 and 50. In the first case, hogging predominate
usually
strains
and the lower
tension
in
ordinary
would be expected, causing compressive sional
the upper
Since
below.
stresses
material
In the second case, sagging strains upper works and ten-
stresses in the
to
be
of inertia calculations
for
rivet
moment
the
in
the
upper material being in
the
vessels,
compression.
in
holes
require
deducted hogging
from
strains,
and from the lower material in that for sagging strains, obviously a separate calculation is needed for each case. Dr. Bruhn* has pointed out that the necessity of two calculations may be obviated by obtaining the moment of inertia without correcting for the rivet holes, the stress
so obtained being after-
The
wards increased inversely with the reduced sectional area.
by
method do not
this
the work
differ
much from
In the following example we show in of inertia for a cargo steamer of
sum a of
It
will
of rivet
inertia,
position
be observed that the
of
holes the
in
the
a frame.
at
first
neutral
instance,
It is
sectional
full
one,
while
to
areas
axis
of the
moment
of inertia
moment
next
about the neutral
obtained from that about
property of the
is
the
assumed
moment
hogging bending
are
tabulated,
the
as an allowance for
about that
;
\
the
find
to a
be noted that the moment an assumed axis, the
also
will
obtained
being unknown
axis
and the assumed one
neutral
is
how
detail
modern type subjected
of those of the parts in tension being reduced by
line
results obtained
ordinary
less.
is
moment.
by the
those
the
distance
determined,
which
and
between the the value
that
what we require, by employing the well-known
axis,
axis,
is
of inertia expressed by the formula
:
I=
I - A x
h2
.
Where / = moment of inertia about neutral axis. I = moment of inertia about assumed axis. A = area of material in section. x
h
=
distance between axes.
This principle is also employed in the first instance to obtain the moment each item about the assumed axis. For items of small scant-
of inertia for
lings in the direction of the
with -
sufficient
depth of
girder,
the
moment
accuracy by multiplying the areas
of inertia
is
expressed
by the squares of
their dis-
See his paper on Stresses at the Discontinuities of a Shifs Structure^ read before the Naval Architects in 1899,
Institution of
;
SHIP CONSTRUCTION
64
AND CALCULATIONS.
tances from the axis as in column 7. In the case of the side plating, however, and the vertical parts of the double bottom, such as the centre girder, margin plate, and intereostals, the figures of column 6 have to be increased by the
moment that
of
TV
is,
each item about an
of
inertia
A d\ where d
is
through
axis
the depth of the item,
of gravity,
centre
its
and A the
sectional area
these quantities are given in column S.
The moment on
material
of inertia
any
at
quickly found, since It
special
/ in
should units
feet-
be
are
being obtained, the stress in tons per square inch
distance
p =
M —
//,
either
above
or
below the
neutral
and inches 2
is
y.
remarked that when applied to a large girder employed,
axis,
M
being in foot-tons, A in
sq.
like
inches,
y
a ship, in
feet,
.
Moment
of Inertia Calculation.
(Ship under a hogging strain). S.S.
350' o" x 50' 74" x 28'
Depth from base
line to bridge
o".
Assumed
deck, 36' 10
neutral axis above base,
feet.
Below Assumed Axis.
Items.
16' o"
MOMENT OF INERTIA CALCULATION. Above Assumed Axis.
Items.
65
—
—
66
AND CALCULATIONS.
SHIP CONSTRUCTION
of the
displacement
instance
by the
multiplied
—
we
length,
have in the present
shall
:
Maximum
bending moment
=
=
5l_
§
96000
tons:
ft.
35
and
if
we use
that just obtained for the value of
figure with
this
get for the greatest stress acting
Mr —
pe To
vessel
we
,
when under a hogging
shall
strain
,
QOOOO
/ = —
I2314
~y
out, a
on the
—
.
.
= 779
tons per square inch.
obtain the greatest stress under a sagging strain, as previously pointed
new moment
of
inertia
similar to that just explained
With regard
to
calculation
the work
necessary, otherwise
is
and need not be here
is
detailed.
the magnitudes of calculated stresses,
may be
it
said that,
Small vessels have to be
generally speaking, these increase with size of vessel.
local strains, and are probably too strong, considered as floating At anyrate, their actual calculated stresses, of which records are available, show these to be very small indeed. In 1874, Mr. John investigated the longitudinal strength of iron vessels of from 100 to 3000 gross tonnage, on the basis of Lloyd's scantlings, the following being some of his results built to
resist
girders.
:
Gross tonnage of Ship.
Tensional siress in tons per square inch at
Upper Deck.
IOO
1*67
5 00
3"95
IOOO
5'2
2000
5*9
3000
8*09
Later calculations for steel vessels of large
size,
which have proved
satisfactory as
show maximum stresses of between 8 and 9 tons and even higher The Servia, a passenger and cargo vessel of 515 ft., had a calculated stress at the upper deck of 10*2 tons per square inch when on the wave crest, and of 8 o4 tons when in the wave hollow, while the Maurelam'a*, of 760 ft. length, is stated to have a calculated maximum stress of 10*3 tons on the top member. It should be added that a special high tensile steel was largely used in the construction to strength,
-
of the upper works of the latter vessel.
With regard plating
is
to compressive stresses,
liable to
it
under a sagging as under a hogging
efficient
particularly
has
when considering maximum already
important to note that thin deck
is
buckle when in severe compression, and
been pointed
out
strain
stresses
that
;
this
is
therefore not so
should be borne in mind,
on bridge and awning-decks.
stresses,
such
as
the
above,
are
not the actual stresses experienced by the vessel, since the conditions of
figs.
It
49 and 50 do not
fully represent
those of a vessel
among
example,
if
waves.
The
results,
In the case of a proposed vessel, for the calculated stress be not greater than in existing vessels whose
however, are valuable for comparison.
*
See the Shipbuilder
for
November, 1907.
SHEARING STRESSES.
67
new
recoids have been satisfactory, the scantling arrangements in the
be considered adequate. calculated
when on new
material
vessel,
be
will
it
to
as
/.*.,
maximum
be much
which
shown
have
far
possible
as
efficiency
most
the
that
clear
bending,
resist
be either
will
manifest
From
from
the
in reducing the
neutral axis, as
may
weakness
our previous
position
it
will
the
for
or bottom
top
the
of
signs
economical at
ship
approximate to the
greater, so as to
then additional strength must be added.
service,
considerations,
it
vessels
in
stress
If
of the
there
be
of
stress.
SHEARING STRESSES.— We come now to consider the We have already explained how the
ing forces on a structure.
effect
of shear-
values of such
may be obtained
at all points in the lengths of beams, including floating under various systems of loading, and we have now to determine the stresses caused thereby.
^forces
vessels,
Fig.
the vertical
If
obviously write
shearing
force
at
62.
any
Mean
stress per
square inch /
A
where
the
is if
shearing
force
from
In
stress per square inch
stress,
62
we have
ported at the
maximum
F,
we may
F_
A
'
of 64 tons, then
mean
fig.
as
number of square inches of material in the section. For beam of section 8 inches by 4 inches be under a
actual stress at any point this
taken
a rectangular
Mean The
_
\
due to shearing force example,
be
section
:
as
we
of the shall
at the point
section
64
8x4
=
2
tons.
may, however, be very different to show.
now proceed
the diagram
middle and loaded
=
at
of bending
each end.
moments for a beam The bending moment
of application of the support, and
has
supis
a
zero values at
68 each end.
may be the
For any two
read from
beam
the
Section Aj A 2 being
has
mid-length
nearer
may be considered
the neutral surface,
/!//!/,
which the upper one
into two portions, of
to
and
in tension
is
lower in compression.
now
Consider
equilibrium
the
shown enlarged in fig. and on the end A 3 L.
moment than
the
tending
move
to
the
the
is
Clearly, the
magnitude of
balanced
R and A 3 L
and
will
the
stresses
difference
portion
This action ends A X
of a small portion of the
beam A
X
RLA
Z,
There are pulling forces acting on the end A r R As the former section is under a greater bending
63.
latter,
be a force equal to
zero,
A x A 2 and A 3 A^ the bending moments
vertical sections
diagram.
the
bending moment.
greater
divide the
AND CALCULATIONS.
SHIP CONSTRUCTION
At
by a
of
the
the
of
shearing
this
shearing
the
top
gradually increase
There"
greater.
forces
total 1
L Az
over
the
force
beam
the
approaches
63.
N
mid-length.
towards
bottom surface L -
where
force it
R.
of the
the areas
shearing /I/,
thus
will'
on the ends
acting
force will vary with
RL
Fig.
be
beam A R
of the
as
.
also
will
will
will
be
be a
SHEARING STRESSES.
69
/ = Moment of inertia of the whole section (in inches q = Stress per square inch at the given point. b = Breadth of beam in inches at the given point.
4
).
Let us apply the formula to the case of the rectangular beam whose mean shear stress was found above to be stress intensity at the neutral axis
16 X
=
a
2
tons.
2
x 12 x 64 3
=
stress
we get
for the
is,
-1
,
3 tons per square inch.
4 x 32 x 64
Thus the maximum shear
Substituting values,
:
in
this
50 per cent, greater than
instance,
the mean.
The above is for a simple beam of rectangular section, but the same In the may also be applied to the more complex case of a ship. latter instance, of course, the beam is of hollow section, and b will be twice formula
the thickness of the shell plating.
It
is
important to note that only continu-
ous longitudinal materials must be used in rinding A. of the shearing stress
maximum end
will
Obviously,
is
a
in ordinary vessels at about one-fourth the vessel's length from each
so that at the neutral axis at these points of the length
;
stress
the value
which
vary with P, the vertical shearing force,
may be
We
considerable.
see
now why
reduce the scantlings in the vicinity of the neutral
shearing
the
inadvisable
is
it
to
unduly
axis.
important to give special attention to the rivets in the landings,
It is also
or
longitudinal
to
a
tendency
seams, in for
neighbourhood, as
this
edge
the
of
one strake to
shear
the
slide
over
stress
that
of
gives
the
rise
next.
Recent experience with large cargo vessels has shown that the usual plan of is only sufficient for vessels up to a certain size,
double riveting the seams say
450 or 480
feet
in,
Longer vessels
length.
will
develop weakness at the
longitudinal seams unless precautions be taken to increase the strength of the
Lloyd's
riveting.
Rules now require treble riveted edge seams
bourhood of the neutral axis above length and beyond.
in
the
TRANSVERSE STRAINS.— So which tend to ably of
first
strain
fore
far,
and
after
we have
in
the neigh-
bodies in vessels of the
dealt exclusively with stresses
a vessel longitudinally, and while such stresses are prob-
importance, we must not omit to refer to those which
come upon
a vessel in other directions. It
verse
has been customary to consider stresses which tend to change the trans-
form as next in importance to those affecting a vessel
longitudinally.
Structural stresses in other directions are, indeed, partly, longitudinal transverse,
effect of their
combination in a
nately, the subject of transverse
and
partly
known for any vessel, the diagonal direction may be predicted. Unfortustresses of ships is a complicated one, and we
and where the predominant
stresses
are
cannot do more here than indicate generally the external forces which operate
on a
vessel
so
as
to
alter
arrangements which best
her transverse form, and point out the structural
resist
this
deforming tendency.
SHIP CONSTRUCTION
7°
Consider in
The
this
hull surface
is
AND CALCULATIONS.
connection the case of a vessel afloat in
still
water
(fig.
64).
pressed everywhere at right angles by the water pressures,
indicated in the figure by arrows, and the resulting tendency
is
towards a general
Taking the transverse components of the water pressures, these obviously tend to force up the bottom and press in the sides, as shown exaggerated in fig. 64. Such tendencies, however, are prevented from becoming actual strains by the internal framing. The comparatively thin shell plating, which might yield under heavy water pressure, particularly in the way of an empty compartment, is kept in shape by the frames, rigidly deformation
of the
form.
vessel's
connected to the beams and to the
floors at their top and bottom ends reand supported between these points by hold stringers and keelsons. In way of the bottom, the deep floors, spaced at comparatively short intervals, and fitted, in the first instance, as supports to the cargo, are splendid preservers
spectively,
The
of the form.
floors,
too, are tied to the
Fig.
beams of the decks by means of
64.
TTTrrr^ strong pillars, and in this ture
communicated
is
of transverse
to
way a it
stress
which comes upon one part of the strucProbably the most efficient preservers
as a whole.
form are the athwartship
may be
steel
Where
bulkheads.
these
occur
and care should be taken to spread this excess of strength over the space unsupported by bulkheads by means of keelsons and hold stringers. Docking Stresses. A vessel when docked or when aground on the keel the vessel
considered as absolutely
rigid,
—
particularly
action
if
of the
loaded, has
to
withstand
severe
transverse
while the weight of cargo out in the wings will set
bending shown,
moment and cause much exaggerated of
up a considerable transverse
the bilges to have a drooping tendency. course, in
fig.
65.
be one having ordinary
turn of the bilge, as
floors,
There
will
be
tensile ;
This
is
stresses
and
if
the
weakness may be developed at the lower
the framing has there to withstand a shearing stress
to the weight of the cargo above.
re-
up her bottom
of considerable magnitude acting along the top edges of the floors vessel
The
tresses.
weight at the middle line will tend to force
The
floors
due
should therefore be kept as deep
7i
transverse strains. as possible at the bilge,
having double bottoms
and should be this
up the
carried well
part of the structure
is
In vessels
sides.
very strong owing
to
the
deep wing brackets, which bring the resisting powers of the side framing into operation.
The
Fig.
fitted; these will act as struts
which
will resist
together. will
be arrested by the
straining at the middle line will
65.
and communicate the
Thus, as in the case of
deck beams,
water tresses, the straining tendency
still
causing equal distribution of stress throughout,
and
stresses to the
a tendency to spring in the middle and to bring the sides
be resisted by the structure as a whole.
design,
pillars, if efficiently
special pains should
be taken Fig.
This interdependence of parts, is what should be aimed at in
to ensure efficient connections.
66.
—
Transverse Stresses due to Incorrect Loading, A preventable cause is that due to the manner in which heavy deadweight
of transverse straining
cargoes are sometimes loaded. the middle
line
of the
vessel
Frequently, the heaviest items are instead
wings having therefore comparatively
of being spread
little
secured at
over the bottom,
weight to carry.
The
the
straining ten-
SHIP CONSTRUCTION
72
dency in such a case
is
AND CALCULATIONS.
to elongate the transverse form, the water pressures
the sides tending to the same end.
This condition
dotted lines representing the normal vessel,
The
is
illustrated in
and the
full
fig.
vessel
the
lines
on
66, the
as
and bottom of the structure, but not unfrequently the rivets connecting the pillars at top and bottom have been sheared in places with consequent dropping of the bottom strained.
pillars
will
be here called upon to
tie
the top
part of the hull.
—
Transverse Stresses due to Rolling. We have pointed out that it is when among waves at sea a vessel meets with the most trying longitudinal stresses, and it may now be added that tendencies to transverse straining are also greatest then. These latter stresses probably reach maximum values when a vessel is rolling in a beam sea, and they are obviously due to the resistance which the mass of the structure offers to change of the direction of motion o each time the vessel completes an oscillation in one direction and is about to
The
return.
stress
is
a racking one, and tends to alter the angle between the
Fig.
67.
deck and the sides, also to close the bilge on one side and to open Such a racking strain is exhibited graphically in fig. 67. other.
The
parts
of
the
structure
form are the beam knees, heads, and any.
the
most
transverse
ordinary side
effective
frames, in which
The beam knees should be
of good
preventing
in
web frames
bulkheads, is
included
this
or
the
it
on the
change of bulk-
partial
reverse
bar,
if
connected to the frames and beams, and fitted well into the corner formed by the side plating and the deck. Change of form at the bulkheads is practically impossible, if they be fore
close
mum floors
stiffened
be given to
sufficiently this
against
point.
The
size,
collapsing; side
efficiently
careful attention should there-
frames, owing
to
their
position
and
spacing, offer powerful resistance to racking, but in order to attain maxiefficiency they should be securely riveted to the beam knees, and the
or tank
virtually
brackets should
be carried well up the
reduce the length of the frame, and
the length
in
it
such a case greatly increases the
is
sides.
well
rigidity
These brackets
known
that
reducing
TRANSVERSE STRAINS.
Local Stresses. have
vessels
to
example, the
—Besides
resist
other
and
engines
longitudinal
and transverse due to
tendencies
straining
with
boilers
73 stresses,
For
causes.
form a heavy
together
seatings
their
structural local
permanent load on a comparatively small fraction of the length, and thus give rise to considerable local stresses. These are provided against in various ways, some details of which are given in a later chapter. It may be said that the general principle is to increase the strength of the structure in way of the loaded zone,
by means of longitudinal girders and otherwise, distribute
and,
the load to the less strained portions of the hull beyond.
Other stresses due to the propelling machinery are those brought on the by the action of the propeller itself. These are most severe
stern of the vessel
and pitching among the waves, and consist chiefly propeller and checking of the same, as it rises out of and sinks into the water. The parts that suffer most are the connections of the stern frame to the vessel, and it is highly important, therefore, that these should be made amply strong. We shall see presently, when we come to consider details of construction, what the usual
when
the vessel
is
rolling
of vibrations caused by the frequent racing of the
arrangements are in such cases.
—
Panting Strains. These strains, which are usually developed in the shell forward and aft, where it is comparatively flat, consist of pulsating movements of the plating, as the name indicates. They are partly due to blows from the sea, and partly to the resistance offered by the water to the vessel's
plating
progress as she is
she
for
is
The
by these
troubled
and her
slower,
than the
flexibility
flatter
strains
to
as
;
with a short
vessel
be
a tendency to
strengthen the shell against panting,
fairly
large,
the
well to
it
the
is
to
fit
a
shell plating
should be associated
stringer
of beams, which act as struts and prevent
movement
in the
In very fine vessels the floor-plates should be deepened forward and
plating.
A
aft.
the
if
tier
passenger steamer,
resist
faster boat.
hold stringer in the vicinity affected, and connect
and framing
ordinary cargo vessel
a fine-lined
ends are better able to
full
form of the
means taken
usual
An
driven forward by the propeller.
is
much
not so
panting arrangement for a cargo steamer
is
shown
in
the chapter
on
practical details.
A
class of strains
somewhat akin
developed under the bows of
full
to those of panting are frequently found
shape of loose
cargo vessels, in the
rivets
They are now recognised to be and generally shattered riveted connections. due to the pounding which a vessel receives from the waves as she rises and falls
after lift
among them. As might be expected, a voyage made in ballast trim, for the
the fore end high out of the water,
force.
It
is
scarcely
wonderful
that
they are
and the next bring this
pounding,
long voyage, should produce the results mentioned. ing
is
of vital importance, and that this
interests,
found much aggravated
pitching motions will one instant
is
it
into
repeated
it
with
terrific
throughout
a
Obviously, efficient ballast-
the opinion of those having shipping
was evidenced by the appointment of the Royal Commission, under
Lord Muskerry,
to consider
the desirability of fixing a
minimum
load-line
to
AND CALCULATIONS.
SHIP CONSTRUCTION
74 sea-going vessels,
although,
various
for
reasons,
there
was no practical
result
therefrom.
—
Strains due to Deck Loads, etc. These loads consist of steam winches, The resulting stresses can windlass, donkey boilers, steering gear, etc. usually be counteracted by an efficient system of pillaring, with perhaps a few the
beams
extra
if
the weights be very great.
The Racking
Strains brought on the deck of a
size
sufficient
to
by
stresses
vessels
not of
sailing vessel
In
from the rigging and masts should be mentioned.
sailing
require a steel deck, special tie-plates should be arranged in
a diagonal direction so as to communicate the stresses from the plating round
mast
the
to the
deck beams and side
stringers,
to all of
which the
tie-plates
should be securely riveted.
QUESTIONS ON CHAPTER
IV.
W
Given a beam fixed at one end and loaded with a weight tons at the other, describe the system of forces acting at any section, neglecting the weight of the beam. If the beam be 10 feet long and the load 2 tons, plot the diagrams of shearing forces and bending moments, and give numerical values for a section 4 feet from the free end of the beam. i.
* m _fS.F.,2tons. \B.M., inch ,
96
-
tons.
Referring to the previous question, if the given load be spread evenly over the beam, indicate the forms which the curves of bending moment and shearing force will then take. 2.
A
beam 20 feet long supported at each end has a. load of 3 tons concentrated at a 3. point 2 feet from the middle of the length. Draw the diagrams of shearing forces and bending moments, and indicate the value of the maximum bending moment. Ans. Max. B.M. = 172-8 inch tons.
—
Assuming the load in the previous question to be evenly distributed over the length of the beam, calculate the maximum shearing force and bending moment, and indicate the points in the length at which these are in operation. f Max. S.F. = 1*5 tons acting at points of support ^ ns \Max. B.M. =90 inch tons acting at middle. Show that diagrams of S.F. and B.M. may be derived by a graphic process, and 5. employ in your explanation the case of a beam fixed at one end and uniformly loaded. 4.
Explain how to construct a curve of loads for a ship floating in still water, and state you would apply to prove the accuracy of your work. What is the connection between curves of loads, shearing forces, and bending moments, 7. and show in one diagram the approximate forms these diagrams would take in the case of a cargo vessel floating *' light" in still water. 6.
what
tests
A
box-shaped vessel 200 feet long, 30 feet broad, 20 feet deep, floats in still water at 8. If the weight of the vessel be 1000 tons uniformly distributed, and if a draught of 10 feet. there be a cargo of 715 tons uniformly distributed over half the vessel's length amidships, draw the curves of S.F. and B.M. and state the maximum shearing force and bending moment Max S F = *78'5 tons. Ans * ns
_J
'
-
-
-
\Max. B.M. = 8925
feet tons.
and top and bottom of
vessel in previous question are plating \ inch thich, find the greatest stress to which the material is subject 1 hogging moment of 8000 feet tons. Ans. '82 tons per square inch. If the sides
9.
—
composed of under a
steel
maximum
—
10. Assuming a cargo steamer in loaded condition to be poised on the crest of a wave sketch roughly the curves of loads, shearing force and bending moment.
11.
Referring to the previous question, at what points approximately in the length will the shearing forces act and where will the maximum shearing stress intensity be developed?
maximum 12.
shearing
Taking the box vessel of question force of 400 tons, find the mean
maximum
shearing stress.
,
and assuming her to be under a maximum shearing stress over the section, and also the /Mean shear stress = '66 tons per square inch. \Max. shear stress = 1*82 ,, 8,
,,
13.
Enumerate the various
local strains to
to strengthen the vessel against them.
which ships are
liable,
and the methods adopted
CHAPTER
V.
Types of Cargo Steamers.
NOT
among
the least
suitable
the
many important
as to cost,
weight capability, and yet failure, in certain
ship,
the question of
is
A
type.
Every owner of experience
trades.
he gets a ship suited
careful to see that
by an owner
points to be settled
ship may be may be strong enough, have good speed and deadmay prove herself very unsatisfactory, if not an utter
upon a new
in deciding
aware of
is
and
this,
is
to his purpose.
Nowadays, an owner who knows his requirements can usually get them But this was by no means always the case. At one time it seemed to be thought that ships must be built to certain fixed carried out in this matter.
and cargoes had often
designs,
rather than the latter being
With the expansion
a vessel's arrangements
suit
the former, resulting in
in oversea trade, however, but
changes in materials ot
and the progressive
construction
— from
of the age,
spirit
wood
more
much annoy-
especially with the
and iron
to iron,
become almost
trades, has
to special
to
came a gradual evolution of
to-day has reached a high standard of
the cargo steamship of
steel
type, until
and
excellence,
the last word of efficiency
purpose intended.
for the
The to
be adapted to
to suit
and expense.
ance, inconvenience,
where applied
to
made
which have marked
variations
present
their
stage
following directions,
viz.
of
strength suitable
in
general
:
—
trades
and appearance
outline
have been, generally speaking,
vessels
the
in
(i) in design of structure to provide hulls of degrees
different
for
and brought cargo
this evolution
development
of
;
;
(3)
form of immersed body and
(2)
in
in
disposition
of
materials
(4)
;
in
internal construction.
STRENGTH TYPES.— It
was long ago recognised that
of great
density, for
weight, such as carried
general
strong
in
hold space
iron
;
instance, which
ore
vessels
occupy
little
space
in
machinery, and heavy general
having great
draught
:
that cargoes
comparison with
cargoes, should be
and displacement and limited
and cargoes of less density, such as grain, cotton, wood, and light
cargoes, should
capacity, but
or
economical
for
working different cargoes should have different classes of vessels
less
be accommodated
deadweight
Lloyd's Rules provided special
capability.
in
ships
schemes of scantlings 75
of relatively
Thus, until
their
for
greater
recent
hold
revision,
three strength types,
viz.,
AND CALCULATIONS.
SHIP CONSTRUCTION
76 three-deck,
and awning-deck
spar-deck,
Of
types.
first-named
the
these,
was the strongest, and was reckoned to be able to carry any kind of cargo to
any part of the world on a greater draught than any other type of vessel of equal dimensions. With regard to the spar and awning-deck types, we have the
of
authority
the
Mr. Martell, a
late
carriers.
The upper
and
weather
the
former
'tween decks were really meant to
and
deck
the
surveyor
chief
and
plating
shell
accommodate passengers, framing
side
second or main deck, were allowed to be of comparatively
But although
thus
built
of
than the
smaller scantlings
deck vessel of same absolute dimensions, these
light
above
the
construction.
corresponding three-
lighter vessels
were not of
less
Their draughts were restricted, their loads reduced, and
comparative strength.
hence also
Lloyd's
to
not originally intended as exclusively cargo
Register, for saying that they were
the leading
movements acting upon them
materials were quite sufficient to ensure as low a
so
;
that
thinner
their
on the
stress per square inch
upper and lower works as in the corresponding three-deck type of
vessel.
In the development of ship construction, the foregoing types have undergone modification. In Lloyd's latest Rules, only two distinct standard types are
mentioned,
The
latter
the
viz.,
has
full
scantling
and an awning or shelter-deck
vessel,
type.
the characteristics of other vessels of the class, namely, light
still
draught and large capacity, but has otherwise been greatly improved.
FORM TYPES.— With regard to changes of form, it must be admitted that body of the modern cargo steamer is no thing of beauty. The sentiment which demanded fineness of form and grace of outline has passed away under the the
From
pressure of ever-increasing competition. of from
the fine-lined under water bodies,
and the nicely rounded topmore or less vertical sides and bluff ends, with displacement co-efficients ranging from '8 upwards. Certainly this side of the development of cargo ships has not proceeded on
with displacement
co-efficients
we have come
sides of former days,
*6
to
to sharp
7,
bilges,
aesthetic lines.
Appearances apart, however, and considering making standpoint, the changes have been in searches of the late Dr. Froude and others, and vessels, has shown that at moderate speeds like
— the
the case from a purely
the
right
money-
The
direction.
re-
experience gained from actual 8 or 10 knots
— the
speeds of
be overcome in propulsion is largely due to surface friction, the element of wave-making resistance only becoming As a considerable increase in displacement and important at higher speeds. deadweight capability can be obtained by a moderate increase in in therefore surface, the easiest and cheapest way for an owner to increase the earning ordinary cargo
vessels
power- of his vessel
become the order
is
resistance
obviously to
Of
of the day.
fill
fullest
should have .
co-efficients.
small
rise
of
her out forward and
course, for the
process must be done with judgment.
with the
to
An
and
and
expert designer can do
In general, vessels floor
aft,
relatively
this
has
best results, the filling out
of
sharp
'8
blocks
bilges
much even
and upwards
amidships, thus
allowing most of the fining away to be done Lowards the extremities.
In some
TYPES OF CARGO STEAMERS. cases this
former
method has not been
rules,
followed.
It
77
should be said that in Lloyd's
the half girth appeared as a factor in calculating the numerals, and
this
induced some builders, for the sake of getting
full
cargo vessels with abnormally fine midship sections, thus causing the ends
to
be very clubby.
factory.
But such
They were found
when
vessels
difficult to
scantlings,
design
to
invariably proved
built
and
steer
lighter
unsatis-
unmanageable
therefore
in a
seaway, also harder to drive, than vessels of 'similar block co-efficients designed
on normal lines. Under the new rules the girth does not influence the numerals, and there is now no temptation to design freak ships of the kind mentioned; still, owners should not take too much for granted in ordering their cargo "tramps," but should see that they get a maximum of good design with any given conditions.
More striking than the changes of the under-water forms, and those which have caused cargo vessels to be classified into various form types, have been those due to the imposition of deck erections on the fundamental flush-deck steamer. Very early in the history of the iron merchant ship, the necessity of affording
some protection
being covered by small
to the vulnerable
bridge
machinery openings led to the
Then
erections.
the
having the crew on deck caused the accommodation for the
from
below and
fitted
in
a forecastle, this
admirable shield from the inroads of head
erection seas,
latter
obvious advantages of latter to
be raised
incidentally forming
and the
release
of the
an
space
under deck making a desirable addition to the carrying capacity. Finally, poops were fitted, experience showing the necessity of raising the steering platform from the
level of the
whose outlines are fig.
upper deck.
characteristic of
arrived
at,'
to-day (see
68).
The
next step in the development of deck erections was in the direction
of increased lengths, as, under in
Thus the three-island type was many of the cargo steamers of
1890,
Government Regulations, which became operative
considerable reductions
particularly
as,
provided
they
in
had
freeboard
openings
could in
their
thereby be
end
gained, and,
bulkheads,
which,
however, might be closed in a temporary manner, the erections were allowed to be exempt from tonnage measurement. Thus long bridges became common, and eventually vessels were built with bridge and poop in one, making, with a disconnected forecastle, one form of the well-deck type (see fig. 69). Fig.
68.
Fig.
69.
e&e
73
SHIP CONSTRUCTION
m
AND CALCULATIONS.
Fig.
70.
Fig.
71.
f
^
|
£&6
Fig.
72.
m
i>
0j-°
The obvious advantage of having a continuous side and deck, and the admirable shelter which the enclosed space would afford for cattle, etc., very soon produced the suggestion to fill in the former gap between forecastle and bridge; and this was rapidly carried into effect when it was found that
by
having one or more openings in the deck with no more than temporary means of closing, the space would escape measurement for tonnage. In this way the shelter-deck type (see fig. 70) was evolved— a type in recent years much run upon for large cargo vessels, and which, as previously mentioned, is now a standard of Lloyd's rules.
Other modifications have consisted of short bridges on longer ones and on these can hardly be considered as constituting distinct
shelter decks, but
For
the
types.
smaller
classes
of
cargo
carriers
steamer has been developed, familiar to
all
who
a
somewhat
special
type
of take an interest in ships, as a
quarter-decker, which, in reality,
is a one or two-decked vessel with the' main This raising of the after deck was undoubtedly due to considerations of trim. It was found that owing to the finer form aft and the large amount of space taken up by the shaft tunnel, the tendency
deck
raised (see
aft
fig.
71).
the normal deck line was to trim by the head
of cargo at the fore end causing
when
with loaded, the predominance
To
correct this state of things the hold was increased by raising the deck. While the quarter-deck has certain advantages, such as good trim and general handiness, it has some drawbacks, one of which is the difficulty of
space
making up the strength plan
this.
aft
is
to
stringers in
lapped.
double the
break of the main deck. The usual and overlap the main and quarter deck
sufficiently at the
shell
plating
way of the break, the hold
In vessels of a
size requiring
stringers at this part being also overa steel deck or part steel deck, the latter
TYPES OF CARGO STEAMERS.
79
overlapped where broken to form the quarter deck, and the two portions connected by substantial diaphragm plates. The doubling of shell and over-
is
lapping of stringers
The
also carried out.
is
something equivalent,
foregoing, or
good the
of continuity.
loss
bracketing and troublesome
It
work, which tends to raise the
the vessel.
In the vicinity of the break,
space;
in
yet,
spite
of
all,
for
some
there
too,
cost of
first
much broken
is
type
this
trades
to make amount of
what must be done
seen to involve a considerable
is
fitting
is
stowage
remains a strong
still
favourite.
Another modified type, in some respects the opposite of the last in that it leads to an increased hold capacity forward over the normal type, is the It is to be supposed that with ordinary cargoes this partial awning-decker. type would trim badly, but it appears to have been found very suitable for It was at one time very popular, but of recent special light bulky cargoes. years has not been
awning-decker forward well
filled
strength
the
One
at
clear
doubtedly the
much
shown
is
The
It is
72.
fig.
external appearance of the partial
seen to be a quarter-decker with the
and the precautions already described
in,
the
in evidence.
in
break have also to be taken in
longitudinal
for
maintaining
case.
consequence of the long erections now become prevalent
modern system of
distributing
Bridges which are very short have small the hull proper,
really part of
this
strength.
It
the
structural
otherwise,
however,
with
is
un-
construction.
value, as they are not
and should not be considered
is
of
materials
in estimating the
bridge
erections
of
which must withstand the structural bending stresses acting on the vessels of which they form part. Moreover, it follows from the principles expounded in the previous chapter, that the heaviest longitudinal materials should be placed at the deck, stringer, and sheerstrake of an erection, whether substantial lengths,
it
be a long bridge, an awning or a
the material at a section
which
is
of
maximum
shelter
deck, as the
Modern
value at these parts, reduced.
required to be built in
moment
of inertia of
thereby increased, and the stress under a given load,
is
this
way by
the rules of
vessels are
now
Lloyd's Register and of the
old practice of making superstructures of light strength at the second deck from the top being disthe massing and build This may be considered to mark an important advance in the continued.
other classification bodies, the
scientific construction of ships.
CONSTRUCTION TYPES.— Coming now place in the
construction
internal
reaching character.
Fig.
73*
is
to
the
changes that have taken
of vessels, we find these
the midship
cargo steamer as built 25 to 30 years ago, and illustrates of the time,
viz.,
and deep hold
thin
side
keelsons.
framing,
numerous
The expansion
to
be of a wide-
section of a large passenger
tiers
all
and
the characteristics
of beams, ordinary floors,
of commerce, however, the
opening
See an interesting paper on "Structural Development in British Merchant Ships," by Foster King, in the Transactions of the Institution of Naval Architects for 1907, to which the author is indebted for particulars in preparing some of the sketches in this chapter. *
Mr.
J.
So
SHIP CONSTRUCTION
up of new
trades,
and the
specialising
AND CALCULATIONS. of vessels
increase in the average size of vessels, then internal economies.
led
the
to
The
adoption
incorporated in the
floors.
water
tanks,
ballast
In a later chapter
early modification in the
we
to
their
dry ballast
ultimately
becoming
of
tier
accompanied the in
fitting
of
detail with ballast tanks,
the
gathered from figs. 74 to 85. deepening of the holds by the
73.
beams, required by the construction rules of or sixth frame of plate webs having face
fifth
hold
bars on their inner edges, the
73,
deal
may be
structure was
the time, and the fitting at every
fig.
shall
Fig.
suppression of the lowest
which,
first
modifications in
caused the disappearance from the holds of the
structure,
but their general design and arrangement
An
these trades, led
trouble and expense attending the use of
of
huge plate side girders which, as shown in ordinary
for
various
to
stringers
being deepened to
come
in line
with the inner edge of the plate webs, and the whole forming a strong box-like arrangement which amply made up the deficiency caused by the omission of the hold
and
is
beams
still
(see
fig.
74).
for case cargoes,
eventually led
deepening of the frame girder or another
This
style of construction
sometimes preferred, but the
is
found
to itself,
its
loss
general
long remained in favour
of stowage
capacity, particularly
abandonment
in favour of the the system of framing which in one form
in the cargo steamers building in the yards to-day.
TYPKS OF CARGO STEAMERS,
Si
SHIP CONSTRUCTION
82
A
AND CALCULATIONS.
development which came, although not quite immediately, was size of the hold stringers, which, as stowage breakers, were
natural
the reduction in
found not was
alone
obnoxious
less
sufficient
for
proximity to the neutral
me
ship against
hold stringers of
Their work tripping,
and
now to
than the
all
the
Moreover, the deep side framing
webs.
demands
of local stresses,
bending was comparatively fifteen is
years
keep
to
the
stiffen
and owing
to their
the extent to which these hold stringers assisted
axis,
and
ago,
frames
the shell
in
trifling. fig.
in
76
In fig. 75 those of the
position,
to
is
shown the
present day.
prevent
them
side
between the frames. Fig.
76.
330 Feet Steamer.
Recent experiments made by Lloyd's Register have gone to show that a frame depth of 7 inches (the limit of the experiments) there is no tendency to side tripping, and since then vessels have been built with a re-
up
to
duced number of hold stringers, and in a few recent cases with none at all. Whether the hold stringer will ultimately disappear from the modern ship This, it may be said, as an element of construction remains to be seen. by some naval architects, but the general feeling seems is the view taken to
be in favour of
Improvements the
its
in
retention
in
a modified
the manufacture
broad-minded view now taken
of
by the
steel
form. sections
classification
in
recent
societies,
years,
have
and
made
33
TYPES O* CARGO VESSELS. it
possible
following the
builders,
for
line
of
of simplification
parts,
to
still
beams,
the demands of shipowners for large holds clear of and numerous hold stanchions. Hence has come the well-known singleVessels of a size ordinarily requiring, by Lloyd's former deck type {see fig. 77) and two steel decks, have been built with a rules, three tiers of beams single steel deck and one tier of beams, the structural strength, transverse and longitudinal, being made good by deepening the side frames and inPurely creasing the scantlings of the deck, shell plating, and double bottomfurther
satisfy
stringers,
77.
Fig. 350'
,
of 350
advancement it.
In Lloyd's
depth
of
feet,
will
about
sition
78
stage
51'
0" x 2ff 0".
LINT 0f_BBI0CEJ)KK
still
proceed
latest rules,
31
feet
illustrate?
towards
in
and depths exceeding 28 so
long
provided
the
they
until
and
have attained
appears
it
likely
the
needs of commerce demand
for,
but
so
far
as
up to a moulded we are aware, no
design has been built approaching this depth.
a type which the
as
size feet,
the construction of single deckers is
single-deck vessel of ordinary Fig.
X
have gone on increasing
vessels
single-deck
lengths
0"
pure
may be
single decker.
considered to It
has
be
bulb
in
angle
the
tran-
framing
AND CALCULATIONS.
SHIP CONSTRUCTION
.84
and strong hold beams widely spaced a broad hold stringer. N.E. coast and have builders
hold
vessels
of
proved
highly
satisfactory.
type are an
of this
with
association
in
Many
this
type
important Wearside
and on the and first
arched webs
have
been
The
designers
built
firm.
With the removal of hold stringers and beams, the presence of numerous pillars A middle line row for most became specially objectionable.
trades
is
perhaps
no great
but with
drawback,
350' 0"
X
increased
breadths
at-
78.
Fig. SS.
the
49'
0" X
28' 0".
Lig£0F_8RUCE_DECK
tendant
on
the
steady rise
rows
of
in
general
stanchions
dimensions,
between
now
the
order
of
the
and the side, with For a time, and up to a the ordinary construction, became imperative. certain point, the case of vessels with breadths beyond that at which quarter day,
additional
necessary, was
the
middle
met, without resorting to the latter, by increasbeams and ot the middle row of pillars, but a limit was soon reached, and the question of the omission of pillars had to Hence arose the system of fitting wide be reviewed from other standpoints.
stanchions are
ing
the
scantlings
of
the
TYPES OF CARGO STEAMERS. spaced strong
pillars
closely
spaced
fonnd
in
centre
row has
specially
The
in
of
vessels
heavy great
50
been pillar
deck
with
association
with
pillars
columns
and
breadth
feet
each
in
convenience of the
over the
cost
common
A
have been
few vessels kind,
and
to
these
built
we
SPECIAL TYPES.— Besides may be considered acter,
genius
of shipbuilders, is
the
cases
the
say,
four
by,
arrangement from a it
stowage
stand-
entails a considerable addition it.
27'
3"
to
as
refer
and
3".
34'
be able to dispense with
pillars
presently
the types of vessels already described which
the standard ones, there are others of quite distinct char-
which the needs of commerce,
important
of
now
79. x
so
shall
some
done
rows
many shipowners have adopted
arrangement,
Fig.
of any
being
line
hold are
hold.
latter
SS. 340' 0" x 45' 6"
each
In
upwards.
point can readily be conceived, and although in
in
pillars
work
whole
the
Centre
girders.
one or two quarter
omitted,
35
the
enterprise
Of
have called into being.
well-known
turret-deck
type
of
of
shipowners,
and the most
these, probably the
Messrs.
shows the midship section of one of these vessels, and differences between them and those of ordinary form.
Doxford.
illustrates
the
Fig.
79
striking
86
SHIP CONSTRUCTION
The
principal
departure
is
AND CALCULATIONS. outward form
in the
at
the
which,
topsides,
up with a moderate tumble home, are curved inwards, forming a central trunk or turret. The working platform is on the top of this turret, which runs forward and aft and contains all hatches, deck machinery, derricks, and everything requisite for efficiently working the vessel. The internal framing of the majority of these vessels (see fig. 79) is on instead of being carried
but in recent cases the hold beam and web-frame system no hold obstruction principle has been carried out, hold beams and pillars being entirely omitted, and the strength made good by fitting deep web-plates the wide-spaced
;
80.
Fig. SS.
with fig.
x
50'
0"
x
26'
attachments to the turret deck, ship
3"
and
6".
33'
and tank
sides,
top,
as
shown
in
So.
Among its
0"
350'
advantages claimed for
the
self-trimming
greater
which
safety
ventilators,
etc.,
weather deck
qualities,
;
its
depth
affords to
the
to
better it
all
turret
greater stiffness
and circumstance making
increased
it
owing
this
make
which
it
of
bulk
for
openings,
much
and longitudinal to
over the ordinary ones
suited
vulnerable
being
distribution
possible
type
well
higher
strength,
longitudinal
such than
owing
cargoes as
the
are
the
hatches ordinary
to its
materials,
;
shape
*
the latter reduce the structural weight and thus in-
87
TYPES OF CARGO STEAMERS.
Although it cannot be said that these vessels have a must be admitted that they have been a long time in service, and seem to be increasing in popularity as purely cargo boats. Another type, of which there is now a considerable number afloat, is This class is of normal single deck Messrs. Ropner's patent trunk steamer.
crease the deadweight.
nice appearance,
it
construction to the main or harbour deck; above this there
running
fore-and-aft;
fitted with
the
of
top
hatchways, winches,
the
The
etc.
x
60'
0"
hatchway ends, and the trunk This strongly built centre stanchions.
at
the
suitable for (see
fig.
deck and
is
kept in form by strong beams
x
3"
25'
is
and
33'
stiffened
ship,
like
3".
by webs and supported by
the turret
design,
is
specially
81).
self-trimming arrangements. is
is
working
bulk cargoes like grain, the trunk forming an admirable self-trimmer
The Dixon & Harroway hold
ship
the
a central trunk
81
Fig. SS. 350' 0"
forms
latter
is
plated
in,
the
patent ship
In
is
another type whose speciality
this vessel (see fig.
main frame of the
vessel
is
its
82) the upper corner of the
being carried up in the hold
This corner space is well adapted for ballasting purposes, the high This type is of position of the ballast conducing to steadiness in a seaway. space.
SkiP CONSTRUCTION
88
Co Em CO N X
Co
«
AND CALCULATIONS.
types of cargo steamers. great
longitudinal
39
and is also well suited to resist the tendency to up when a vessel is labouring in a seaway. Self-
strength
transverse change of form set
trimming also forms the chief claim to distinction of the vessel shown in fig. It is seen to resemble the last type somewhat with the corner tanks away; 83. and on the latter account is not so efficient from a strength standpoint.
As
in
aft
platform.
the
Still
Henry
Ropner trunk
vessel,
the
ship
worked from a
is
another variation of the trunk or turret type
Burrell.
Like
the
other
vessels
Fig. SS.
305'
just
referred
is
to
fore-and-
central
that this
devised by Mr.
one
is
self-
84.
0" x 46' 9" x 24' 0"
and
30'
3".
trimmer, and, as well as the upper trunk, has the corners at the bilges (see fig.
a
filled in
84) and the inner surface sloped towards the centre, thus obviating the
broken stowage space which might otherwise occur at the bilges. Incidentally, corners thus cut off from the holds form a desirable addition to the
the
ballast
capacity.
The
webs, and there are
deck,
no hold
sides
and trunkways are supported by cantilever
pillars.
Other special types have been
built,
or are building, differing
more
or less
from the foregoing, but in general not sufficiently to make it necessary to refer One design, however, that of Mr. Isherwood, is of such distinctive to them.
and
interesting a character as to warrant
its
being singled
out.
This
type
is
AND CALCULATIONS.
SHIP CONSTRUCTION
go
framed on
the
and
system,
longitudinal
in
recalls
respect
this
famous
that
the earlier vessel,
work of Scott Russell and Brunei— the Great Eastern. Like with widely the new ship has main frames and beams running fore-and-aft, skin on the double however, no There is, spaced transverse partial bulkheads. that the except type, present-day normal of the sides, the inner bottom being main
internal framing
shows
85
Fig.
is
longitudinal instead of transverse.
midship
the
on
consist
should
be noted, however, that
system.
angles
at
the
settlings
Fig.
increased greater
the
towards
loads, the
the
medium-sized
steamer
cargo
longitudinal
of
bulb
a
of
section
beams and frames are seen wider spacing than on the transverse system.
The
framed
this
of
the
frames
It
are
gradually
to
withstand
85.
bottom of the
intensity
of
to
vessel,
where
the water pressure
they
have
increasing in
proportion to
depth below the surface.
The
transverse
strength
is
made
up
by strong
transverses
or
partial
bulkheads attached to the shell-plating between the frames, and stiffened on The transverses are spaced from about their inner edges by stout angles. 12 feet to 16 feet apart in ordinary cases, according to size of vessel, the largest
vessels
having the closest spacing.
The double bottom, girders,
with
intercostal
as
previously mentioned,
transverse
midway between them, the
latter
floors
in
has fore-and-aft continuous
line with
the
tranverses
and
also
being required to provide sufficient strength
TYPES OF CARGO STEAMERS. docking purposes and bottom through grounding.
for
It
afloat
and
is
this
type
relative
of great
weight than
of vessel,
importance,
the
as
normal
apart
several
may represent, it means for the and therefore increased earning power.
Fig.
The Isherwood system vessels.*
Fig.
86
dimensions of which depth
inches;
is
at centre,
it
The
has
greater
saving
built
angles
of plates
spaced
27
viz.:
29
;
a
capability
86.
of an
oil
steamer framed in
this
way, the
355 feet; breadth, extreme, 49 feet, 5 The longitudinal frames from the deck to
the spacing
apart.
two strong transverses are
is
which
— length,
feet.
and bars inches
cost
deadweight
greater
strength
weight
in first
the upper turn of the bilge are bulb angles as shown; on are
the
samples of which are now
that
any reduction of
vessel
1
of construction appears to be specially suitable for
a section
are,
type.
from
this
oil
come on
the excessive stresses which
resist
and giving good accounts of themselves,
less
point
claimed for
to
9
fitted
is
The main in
each
*See a paper by Mr. Isherwood in the T.I.N. A.
for
29 oil
tank
inches.
tanks
are
between
1908, from which
the bottom they
The beams 30 the
figs.
feet
are bulb long,
and
boundary bulk-
85 arul 86 are taken.
SHIP CONSTRUCTION
92
AND CALCULATIONS.
heads. The transverses are fitted to the shell-plating between double angles and have heavy double angles on their inner edges. The longitudinal frames and beams and longitudinal stiffeners on middle line bulkhead are cut at the transverse bulkheads and efficiently bracketed In way of the thereto in order to maintain the continuity of strength.
double bottom, which alternate line,
transverses
and
the
fitted
longitudinal
and
transverses,
fitted
is
are
a portion of the vessel's length amidships,
for
continuously around the bottom are
girders
attached
efficiently
in
fitted
long
lengths
The remaining
thereto.
to
middle
the
between
these
transverses
are
stopped at the deep girder in the double bottom next the margin-plate, and are
then
fitted
is
intercostally
them by double-riveted
A
comparison
amidships
of
between the longitudinals to the centre line. The between the transverses, and connected to
intercostally
fitted
margin-plate
this
of
watertight
vessel
collars.
longitudinal
the
with
that
stress
acting
acting
on
an
on the bridge gunwale vessel of the same
oil
dimensions built on the ordinary system, showed the former to be cent,
less
estimated
than
the
latter.
saving in weight
In
spite
of materials,
of
this
there
is
stated
to
18J per be an
under the new system, of 275 tons.
CHAPTER
V.
Practical Details.
KEELS AND CENTRE KEELSONS.—The foundation of or steel the
vessels
ship's
consists
structure.
of
At the ends
vessel.
three
a
a it
The
is
scarphed
items together forming a complete Fig. RIDER
running
bar
forged
keel
simplest form
into
may be of
almost
the
stem
and
the
longitudinal
rib.
considered the
keel
fitted full
in
sternpost,
The
iron
length of
bars
the
forming
87.
PUTE
STRAKX
about
40
joined
together by These scarphs are frequently riveted up previous to the fitting of the shell by means of small There is an objection to the tack rivets, so as to allow the keel to be faired. necessary be to remove a keel length, that, if it tack rivets, in use of the
keel
are
fitted
vertical scarphs nine
in
lengths
averaging
feet,
times the thickness of the keel in length.
93
say,
to
AND CALCULATIONS.
SHIP CONSTRUCTION
94 for
repairs
removed
be
order
to
they are sometimes omitted.
and
the
also
apart,
centre
keel
;
the shell, are
to
of large
and arranged
centre,
to
plates on both sides of the keel have knock out the tack rivets for this reason The main rivets connecting the scarphs together,
grounding,
after
in
in
zig-zag
must be taken It
this
although
87,
care
will
keel
be
has
to
seen
to
garboard strakes.
the
For
riveting
keep the
occasionally
is
five
diameters
style,
as
in
88.
Fig.
fig.
diameter, spaced
two rows, usually chain
rivets clear of the
adopted;
in
the
latter
case,
garboard strake butts.
by referring to fig. 8 7 that the only connection that main structure is through the riveted connection to the reason
this
is
it
a hanging keel.
frequently called
Fig. 89.
BAR
HvEEL
:
INTERCOSTAL CENTRE KEELSON
RIDER PLATE
The
simple bar keel
is
sometimes
running along the tops of the vessels, vessels.
and a
vertical
In the largest
and a foundation
plate
plate
floors,
fitted in association
and four
angles,
two top and bottom,
vessels, a rider plate is fitted
on top of
with a centre keelson
consisting of double bulb angles in small
floors
in
larger
on top of the upper angles
below lower angles.
This style of keel-
KEELS AND CENTRE KEELSONS. which
son,
is
depicted in
fig.
87, but
have
no
know
of the bending of beams,
means a the same angles as
to
direct
perfect
connection with
one.
resistance
the
line
as
Bending if
the
without a foundation plate, external
we must separately,
rigidly joined.
of stress
give
95
keel.
see that
the keel
seen to
is
From what we
already
by no and keelson do not offer
the
Moreover, the
arrangement
floors
is
lying
no support, but develop a tendency
at
right
to trip,
shown exaggerated in fig. 88. The weaknesses pointed out in the above may be largely corrected by fitting plates between the floors, from the
plan
Fig. 90. FOUNDATION
PLATE
-,_
AND CALCULATIONS.
SHIP CONSTRUCTION
96
be observed that a practical difficulty crops up in the riveting to the garboard strakes, in the case of a side bar keel, as five There are two thicknesses of plating require to be united by the same rivets. It
will
of the
keel
rivets, of size and spacing similar to the bar keel, and as it is punch these holes before fitting the plates, it can be imagined that very careful workmanship is needed to keep the rivet holes concentric. As a matter of fact, they are frequently more or less obstructed. In such cases,
rows of such usual to
before
proceeding with the plan
objectionable
holes
the
riveting,
of drifting partially blind
punch
The
should be rimered out.
holes
— that
to
is
say,
of driving
so as to clear a known, and has been proved many times in practice, that the bruising which the material round the edges of the holes gets by drifting, renders it brittle and therefore liable a
tapered
bar
round
of
— should
to break away, loose
rivets
An
objection
which they
It
is
drift
into
not be encouraged.
to
projecting
all
always
It
them, is
consequence.
resulting in
common
entail.
or
steel
passage for the rivet
keels
the
is
increase of draught
considered a good feature
in
a vessel,
and
Fig. 91.
FLAT PLATE
KEEL
INTERCOSTAL CENTRE KEELSOM
FLOOR
INTERCOSTAL'
have a moderate draught of water.
particularly in a cargo vessel, to
of course,
that
is
many
The
reason,
open to a vessel, if of shallow draught, These considerations have led many owners keel in preference to the one we have been
ports will be
which would otherwise be closed. what is called a flat-plate In this case, the ordinary shell-plating is continued under the dealing with. vessel instead of being stopped on each side of a projecting keel the middle to adopt
;
strake
line
is
keel of the vessel
be
very
a
keel,
but
centre
(see
is
usually fitted
centre plate
they
on each
side.
are
projecting
keel
is
In
lost.
floor plates
severed at
should be noticed that with a
of the
is
considered to
for the rigid vertical bar of the ordinary conjunction with an intercostal or continuous being connected together by double angle bars.
both
connected by double vertical bars It
and
be the This horizontal plate would of itself
91a).
centre plate, the
plate,
thickness,
in
the two
plate,
intercostal
in
substitute
inefficient
centre
vertical
With an tinuous
it
somewhat figs. 91 and
increased
;
cases
this
is
the
the
keel,
continuous
line,
floor
prevents any
flat-plate It
are
middle
the
;
with a con-
and abut against the and centre plates are
movement rolling
of the
parts.
reducing property
custom, however, in
modern
caro-o
KEELS AND CENTRE KEELSONS. vessels,
at
bilges
The bottom
more
make up
to
the
(see
As
91b).
satisfactory
by
this
75,
type
flat-plate
(fig.
for
figs.
76,
fitting
longitudinal
except
in
of keel
frequently fitted
is
number
when double
angles
rolling
where there
centre
the
plate
is
chocks
is
a double
obtainable
than
much with
angles are not required in this
machinery space, where they are
the transverse
or
the floor plates are then of considerable depth, a
connection with the
bars
etc.).
ordinary shallow floors; by Lloyd's Rules double case,
97
always
necessary,
until
reaches 66, corresponding to a vessel say, 300' x 40' x 26,
are
required
half length
for
Fig.
CENTRE THRO
amidships.
91a.
PLATE
KEELSON
CENTRE THRO PLATE
Fig,
91b.
CONTINUOUS CENTRE GIRDER 1
-
DOUBLE BOTTOM
—
—
qS
SHJP CONSTRUCTION
Length.
— The
the
after
stem
to
length
(L)
be measured from the fore part of the on the range of the upper-deck
to
is
the
of
part
AND CALCULATIONS.
sternpost
beams,
except in awning or shelter-deck vessels, where it is on the range of the deck beams next below the awning or
Breadth. the
— The
breadth
(B)
be
to
is
the
be measured
to
shelter deck.
moulded breadth of
greatest
vessel.
— The
Depth. of keel
to
awning
or
top
depth
of
(D)
beam
be measured
to
is
uppermost
of
side
at
continuous
vessels, where it may be below the awning or shelter deck, provided the height
taken
shelter-deck
Fig. AWN
does not exceed outline
8
feet
midship section
From
these
1
of a
deck,
to
of
the
except
in
deck next
the
'tween
decks
92.
INC OR SHELTER PSjCK OR
B and D
;
from the top
mid-length
at
are
BRlOCEQECK
indicated in
fig.
92,
which shows an
vessel.
dimensions the scantling numbers are obtained
number = B 4- D Longitudinal number — L x (B 4- D). number regulates the frame spacing and
thus
:
Transverse
The the
transverse
floors.
Thus,
taking
a
of
vessel
45
feet
breadth
and
the
scantlings
28
feet
of
depth,
we have Transverse
And under the
this
number we
frame spacing should be of an
middle,
'46
inch
ends.
at
inch
number = 45
find
thick
24 Jfor
4-
28
=
73.
appropriate Table of the Rules that inches, and the floors 30 inches deep at
in
?
the
length
amidships,
tapering
to
-38
of an
Lloyd's numerals.
The is
of the
size
vessel,
The frame
unsupported.
is
beams above the base and beams
at
bilge
the
Reverting
bilge.
Two
d
is
the
one assuming a
tier
to
cases are indicated,
fig.
92,
below the upper deck, another assuming the frame to be It will be observed that bilge to the upper deck.
exist
to
unsupported
the
at
unsupported length of frame. of
are governed by the transverse number, and also by the extent to which the frame assumed to be supported at the first tier of
frames
the
of
scantlings
by the
i.e.,
99
from
the
d
measured from a
is
line
squared out from the tank at side.
Fig. 93.
In the
case
this
line
is
The this fig.
there
bottom
an inner
is
rules
provide
scantlings
figure apparently marking the
93
given,
the
;
when a
has
vessel
ordinary floors,
squared out from the height of the floors at middle.
framing
of
three
and shows how the
of
frames
limit
single-deck
scantlings
of
a
purely
vessels
increase
of
values
for
of
d up
single-deck different
to
The
longitudinal
number
regulates the scantlings
and bottom
plating,
double bottom, side
feet,
dimensions
with increase in size
side
27
vessel.
In is
of vessel.
of the keel, stem, sternpost,
stringers,
keelsons,
lower deck
AND CALCULATIONS.
SHIP CONSTRUCTION
IOO stringer
giving
and lower deck
plates,
proportions
the
plating.
length
of
It
also
is
depth
to
in
employed with a number the
of
scantlings
the
fixing
upper works.
The importance out
materials are concentrated shelter in
less
a deep
The depth employed top
of keel
bridge,
be measured
top deck
the
to
when
the depth
side
at
these
at
proportionately
is
are
parts
shallow.
scantlings
except in way of a short
cases,
all
upper deck, which thus becomes
to the
beyond
the upper deck
at
for
the middle of the length from the
at
in
be taken
to
is
The
the strength deck.
that
obtaining the proportions of length to depth
in
to
is
the
in
Also the scantlings
bridges.
than in one
vessel
use with the Tables
the side
at
and of long
decks,
recognised
fully
is
and depth of girder, pointed Thus the heaviest Rules. and deck-plating of upper, awning, and
of materials
of distribution
IV. }
Chapter
in
the ends
of a
long bridge, are to be determined by taking the depth for proportions to the
upper deck. Shallow vessels, which taken to the upper
midship half length, the
strength
deck,
girder.
In
ship
be
to laid
of
depths,
14
of.
the
to
(see
figs.
be spaced from
shallower
question
of
the
depth
the
namely,
vessels,
of
deck becomes
bridge
the
increase
of
longitudinal
the
having
those
has
strength
be
to
At the
the
collision
the
vessel
37 and
20
fore
to
the
liable
inches apart,
2>Z
from a
sea,
the
inches,
the
fifth
the
to
vessels
-is
probably the most floors.
if
vessel's
pounding
point at which
the
at
built
according to
may exceed 33
end,
at
form of the ship
Frames of
74).
bulkhead, owing
is
frame
extends from the keel to the top of the vessel in
it
the spacing
cases,
made.
As
lieu.
keel the transverse
a transverse plane, and gives
special
depths,
3J
a ship's structure, especially in vessels with ordinary
previously explained,
fitted
1
them.
before
FRAMES. — Next
is
the
in
substantial
still
exceeding
or
to
have a bridge extending over the
to
and Lloyd's Committee require proposals
considered,
carefully
fundamental part
As
means a case
the
equal
lengths
required
compensation
or this
exceeding
lengths
have
deck, are
to
the
size
it
may
Lloyd's Rules of vessel.
In
compensation be length from the stem to suitable
stresses
to
frame spacing should not
which
this
part of
27
inches,
exceed
unless the frames are doubled to the lowest tier of the beams.
In the peaks
the frame spacing should not be greater than 24 inches.
Each complete transverse frame may be made up of two angle frame and reversed frame, as described
Chapter III.;
in
or
bars,
may
it
i.e. %
consist,
a as
many modern cargo steamers, of a single angle or bulb angle or it may be of channel section, with the addition, in the case of a large vessel, of a Lloyd's Rules provide tables of scantlings of frames of these reversed angle. In fig. styles. various 94 the side framing required for the vessel marked A in
in
;
fig.
93
The
is
shown, the three equivalent types being indicated. flange
fore-and-aft
the
transverse
part
attached
flange,
to
a
in
of
a
vessels
floorplate.
frame
is
having
When
the
riveted
ordinary
to
the
floors,
construction
shell-plating, is
consists
at
of
and
its
lower
a
frame
101
FRAMES.
and reversed frame, the to
vessel,
the floor,
the
turn
latter
the
which being thus
to
whence
it
the
on the
frame
sweeps
along
top and bottom,
stiffened at
covering angle
line,
riveted
is
bilge,
the
sides
top
becomes an
the
of
edge
bar straps being
fitted.
The frame
of
efficient
Both the frames and reversed frames are usually butted
transverse girder.
the centre
of
at
butt-straps,
and are placed back with the frame, the floor-plate being between. These heel-pieces should be so fitted as to bear on the top of the keel, when of simple bar type, as in this way stresses due to docking or grounding are communicated or heel-pieces, as they are called, are usually about 3 feet long,
back
to
94.
Fig.
directly to
to
the
vessel's
Where
the framing; .without unduly straining the rivets connecting the keel
garboard length
the middle
not usually fitted; is,
strakes.
amidships, line
Heel-pieces
form
the
keelson
is
are
at
fit
only
ends
fitted
for
three-quarters
the
making them unnecessary.
a centre through plate, the heel-pieces are
and where the former
of course, impracticable to
the
is
associated with a flat-plate keel
it
them.
At the decks, the framing on each cross
beams,
special
attention
side of the vessel is connected by being given to the beam-knee connections, as
the combination of beam, frame, shell-plating
and deck-stringer
in this neigbour-
102
AND CALCULATIONS.
SHIP CONSTRUCTION
hood is most efficient for resisting the transverse racking stresses to which, as we have seen, a vessel may be subjected when rolling among waves at sea.
WEB FRAMES. — When
stiffening
on
angles
a transverse rib
inner
its
edge,
Rules permit a system of web frames at paratively
light
intermediate frames,
of a
consists
known
is
it
as
for
In
is
fig.
shown with web
95, the
frames.
largest It
will
Lloyd's
com-
with
heavier frames
the
of the ordinary frame table, provided a deck be laid on the the height d.
frame.
frame spaces apart,
six
be substituted
to
deep plate with
web
a
of
tier
beams
of the three vessels indicated in
at
fig.
93 be seen that the angles connecting the
95.
Fig.
SECTION SHOWINt
SHOWING
SECTION
INTERMEDIATE FRAME
WEB FRAME
'iNTERWlDiATCl
TfUMES / 6V5V-4ZB-A
webs as
to
the
shell-plating
the webs, and
stringers.
When
bulkheads,
and
Lloyd's angles
A beams,
Rules,
and
angles
to
are
the side stringers are of the fitted
to
same thickness and
the inner edges of the webs
webs become of considerable depth, they are to
connection.
shell
that
develop
their
efficiency
full
should
have
really
a
partial
substantial
Thus webs
require
24 inches and above, in vessels built to double angles to the shell-plating, or equivalent single
double riveted.
web frame being held and at the bilge by
rigidly its
at
floor
the or
deck tank
by side
its
connection
connection,
to
forms
the
a
WEB FRAMES. girder
comparatively
of
which are
stringers,
short
only
span,
properly
make
at
held
103
when
least
compared with the side For this reason
bulkheads.
the
at
web frames continuous and the side stringers done. At the junction of each web and stringer, the discontinuity of the latter is made good by a double angle connection to the webs, and by fitting a stout buttstrap to the stringer face bar (see fig. 95). Web frames are attached by bracket knees to beams at their heads, the knees being double riveted in each arm and flanged on their inner edge. At the lower part, when associated with an ordinary floor, the inner edge of the web frame is swept into the top edge of the former, the it
advisable
is
connection to nection
on
angle
bar
(see
fig.
this
the
be
to
is
angle
to
and
intercostal,
the
to
from
the
usually
is
an
to
margin
bar
overlapped
should
it
with, in addition,
the
of
web on
When
one.
riveted
bottom,
inner
plate,
top
the
an
being
floor
made
consist
the
a
of
con-
riveted
a substantial gusset plate
bottom
inner
the
to
or
plating
95.)
FLOORS.
— These
vertical
plates
be
will
depth, governed by the size of vessel, at the
bending
stresses
depth
line
on the run of the frame, being
three-quarters
maximum
have a
to
where the transverse
line
Thence they gradually taper towards the
are greatest.
the
at
observed
middle
half breadth,
the
sides,
measured out from the middle
From
half that at centre line.
this point,
the upper edge of each floor sweeps into the line of the inside of the frame,
terminating at
a
middle
There
line.
reversed frame
vessels,
the
buttstrap
is
forming,
feature
acteristic
the
line
at
of a
middle
fitted
or
line,
through centre-plate
a vertical
equal
is
in
twice
to
each frame,
its
the
which
depth at the frame,
floor, is
an inner bottom.
built without
vessel
are
floor
a transverse girder,
indeed,
floor-plates
at
from the base
one such
height
and
most char-
the
Except
in
small
two pieces, connected by an overlap or
alternately fitted,
on each side of that
the
floors
are
fitted
line.
close
When
against
it
on each side, a riveted connection being made by double vertical angle bars, The loss of transverse strength due to cutting the as shown in fig. 90. floors is also partly made good by a horizontal keelson plate fitted at the centre line on top of floors, referred to when dealing with centre keelsons. When bottoms
inner
are
modifications, as
fitted,
we
shall
SIDE KEELSONS.
part
this
see
— As
of
the
structure
undergoes
considerable
presently.
well
as
the centre keelson, vessels with ordinary
have keelsons midway between the bilge and the middle
line. The main and floors in their correct relative positions, intercostal plates are fitted between the floors and connected to the shell-plating and to double angles on top of the floors. These intercostal plates need not be connected to the floors, but in order
floors
of these
function
to
develop
their
keelsons being to keep the frames
full
efficiency
should
be
fitted
in
In
larger fig.
vessels,
96,
side
27
feet
keelsons
and under 50 for
vessels
feet
in
of various
between them.
close
small vessels, under 27 feet breadth, one side keelson
is
breadth, sizes
are
In
considered sufficient;
two are necessary. shown.
BILGE KEELSON. addition
in
AND CALCULATIONS.
SHIP CONSTRUCTION
to4
and should be
carried
plating
(see
vessels
fig.
as
a
of
and
in
larger to
of single of
vessels
the
to
stresses
small vessels
connected latter
and
together, in
sisting
aft
54
breadth,
connected to the
plate
side,
This keelson,
practicable.
as
feet
on each
required
is
shell-
96).
SIDE STRINGERS.— Between tied
and under
feet
keelson
forward and
far
Fig.
is
50
bilge
should have an intercostal
a side keelson,
like
— In
two side keelsons,
to
type in vessels of
all
the bilge and the deck
some
extent
distributed
angles
riveted
to
angles
similar
Lloyd's
shell-plating. sizes.
96.
According Fig.
to
by
an
with
require these
stringers
con-
frames and lugs,
reversed
associated
Rules
beams the framing
side
intercostal stringers
Regulations, the
of
plate this
number
97.
A
SECTION
AT A.B.
© ~^r~ of
side
than feet feet,
14 to
stringers feet,
21
three All
is
two
should be
keelson
\_y
depends
that
feet,
7
and
in
are
w
^u
s^7~
B on the value of very
small
necessary;
vessels,
d.
i When
one
is
and when d
this
is
sufficient; is
20
feet
7
feet
and
less
where d is 14 and under 27
fitted.
stringer
plates
and angle
bars,
when continuous, should
105
BEAMS.
be
long
in
fitted
strength,
and
lengths,
to
obviate
any sudden
discontinuity
should be carefully shifted from
adjoining butts
each
the
of
other.
Both
and bars should be strapped at the butts, the angle-bar straps conof bosom pieces of the same thickness as the keelson bar and two long, having not less than three rivets on each side of a butt (see fig. 97).
plates
sisting feet
BEAMS. — A
of
tier
beams
always
is
frames together and support the deck the
strength
in
scribed
(see
of
structure
pages
The number
71,
ship
so
as
to
the functions of
;
are
generally
as
tie
beams
have
the top of the as elements of
been already de-
72).
of beams
of tiers
transverse strength, but
a
fitted
it
also
required in any vessel
depends on the trade
for
is
a
which she
question is
of
intended.
98.
Fig.
ELEVATION SHOWING STRINGER FACl ANCLE.,
Passenger boats usually require one or more decks below the upper one for
Many cargo vessels, owing to the nature of their need one or more 'tween deck spaces; in most cargo boats, howas has been said elsewhere, the desire is for deep holds, clear of beams
purposes of accommodation. cargo, ever,
or
also
other
designer
obstructions.
Lloyd's
latest
Rules allow considerable scope to the
As was seen
matter.
in a previous paragraph, they allow him, up to a certain point, to design his vessel entirely clear of beams below the upper deck, if he so wishes. The value of tf, in such a case, will, of
course,
heavy it
is
in
be (see
this
relatively fig.
obviously
governed by
its
93).
a
and the scantlings of the
great,
This just
span.
is
the
penalty
one;
for
each
side
framing relatively
exacted for unobstructed holds, and frame is a girder, whose strength is
—
—
Io6
SHIP CONSTRUCTION AND" CALCULATIONS.
Spacing of beams, such as in
Beams. is
— According
Lloyd's
to
complete
a
Rules,
scantlings of the latter, may consist of Beams at every frame. (2) Beams at alternate frames. (3) Beams widely spaced up to 24 feet apart. In arrangements (2) and (3) the beams are heavier than
regulating
tier
of
required to form the upper point of support of the frames
the
:
(i)
in
broad
a
(3)
must be
stringer
bar, and large horizontal and the beams (see fig. 98).
heavy
face
stringer fitted
Rules
Lloyd's
frame in the following places
every
at
in
(1)
and
;
on the ends of the beams with a gussets must be fitted between the
fitted
beams
require
to
be
:
(1)
At
(2)
At upper decks of single-deck vessels above 15 feet in depth. At unsheathed upper decks, when a complete steel deck is required
(3)
watertight
all
flats.
by the Rules. (4) (5)
At unsheathed bridge, At upper, shelter, or
shelter
awning
and awning decks. decks
450
over
vessels
in
Under
whether the decks be sheathed or not.
length,
feet
in
erections,
such as poops, bridges, and forecastles in vessels
less than 66 feet upper deck beams may be on alternate frames, except
breadth,
in
one-tenth the vessel's length within each end of a bridge, where
for
they are to be fitted at every frame. (6)
At
the
Elsewhere, only
the
if
in
deck
hatchways,
of
sides
openings,
unsheathed
all
including or
steel
may be spaced
beams
frame spacing does not exceed
those
of
iron
decks.
two
frame
and
engine
spaces
boiler
apart,
but
inches.
27
easy to grasp the reason for close spacing the beams on unsheathed With thin decks and widely spaced beams, the plating would probably sag between the latter, which would make the decks most unsightly; with beams at every frame the sagging tendency will be very slight. The close beam spacing in way of hatches is necessary in view of the heavy weights which may be brought upon the deck there during loading operations. When a wood deck is laid, beams may be at alternate frames (except as above stated in vessels over 450 feet). In this case, the steel deck is supported between the beams by the wood deck, the deck fastenings for the wood deck being fitted between the beams. The beams forming the weather It
is
decks.
decks are usually cambered, so as to throw lower
tiers
sometimes
are
camber given
weather
cambered decks
and
off
water quickly
sometimes
\ inch per foot Lloyd's Rules allow the beams of weather decks to be
or
with
less
longitudinal is
to
than
the
number)
if
covered by erections.
that
usual at
amount,
least
On
is
in
half the
the
length
case of
the principle of the
camber should give additional strength
of
those
The
length
fitted
of
large
the
top
arch,
;
straight.
it
of
of the
usual
beam.
without camber vessels (30,000 continuous deck
might be thought
to beams, but, as has
been pointed
BEAM out,* the
be the
of a
sides
not really abutments, so that this can scarcely
ship are
case.
BEAM SECTIONS.— Beams strength
the
A and
G
and J
only
are
machinery,
to
to
fitted
to
Sections
99.
common D and carry the ship's boats. Sections F frames. to alternate
strength
extra
binding
away owing
cut
built
be
to
where
fitted
material
the
much
very
are
fig.
beams
ordinary
for
in
adopted when the beams are
E, are
section
beams
special
beams
included
being
according
sections
different
of
fitted
these
not often used
is
for
used when
are
are
of
vessels,
large
in
however,
section,
H
and
B,
most
required;
every frame.
at
io 7
SECTIONS.
is
the the
necessity
a
is
way
In
vessel
together
providing
of
it
required.
the
of
sides
;
ample
the
of
usually
is
space
for
it is, therefore, of importand boilers ance to make any beams that may be got across the vessel in that locality as strong as possible; beams similar to those just mentioned are is a form of beam found suitable (? usually fitted, with satisfactory results. for the ends of hatchways, the angle bar being, of course, fitted away from
shipping and unshipping the engines
hatch
the
carried,
order
obtain
to
connections
between
reduced
depth
in
strength at
and
strength,
special
beam ends and
the
towards
beam
and very top
of
inner
of the
shall
consist
now
of
triangular
a
the ship's side, and
Sometimes
for
sections
and
lightness,
edge of the knee-plate
beam
ship
The
reasons for
given
is
having
have already been explained. describe a few methods of forming and
one when the workmanship
efficient
beam and
frame.
of a
knee
substantial
ship
Several examples taken from Lloyd's Rules, of a
knees.
seen to
It is
be
beams are not might be done in the case
frames,
as
of
allow
to
the
extremities,
their
part
this
BEAM KNEES, — We fitting
adopted
99.
of an ordinary loaded girder supported at the ends. great
section
will
by the experience of the designer.
Fig.
In
and the
needed,
are
are
deck weights
heavy permanent
where
general,
beams
strong
specially
dictated
that
In
opening.
;
plate,
well to
is
good,
fitted
riveted
into
is
shown
the angle
to the
at
common, fig.
100.
between the
beam end and
the
minimise obstruction to stowage, the
hollowed.
This knee can be
fitted
to
any
above.
Another way of forming a beam knee is to cut away the lower bulb for a end of the beam, and weld in a piece of plate or bulb This plate, the knee being afterwards trimmed to the size and shape required. short distance from the
is
called
a slabbed knee *
(see
fig.
101).
Unless great care
See Practical Shipbuilding, by A. Campbell Holms.
is
exercised,
the
ioS
AND CALCULATIONS.
SHIP CONSTRUCTION
welds
of
these
popular as
the
knees bracket
will
give
trouble
knee, nor as
this
reason
style
this
one we are about
to
is
not so
describe.
In
100.
Fig.
BEAMS AT
for
;
the
EVERY FRAME
BEAMS AT ALTERNATE FRAMES
C.
MUST NOT BE LESS THAN
Six
TIMES
OlAMETLR OF RIVETS
this
last
of th^
case,
Fig.
101
Fig.
102.
each end of the beam
depth, as
indicated
in
fig.
is
102,
split
horizontally at about the middle
and the lower part
is
turned down;
BEAM KNEES. a piece is
cut
is
welded into the space so formed, and, finally, the beam size. This knee also depends on the quality of the stronger than the previous one, and has a fine appearance
of plate
is
shape and
to
welds, but it
I09
is
it
known As the
a turned knee.
as
are mainly met by the shearing strength of the rivets, must be sufficient in number and diameter. Lloyd's Rules require that in knees under 17 inches deep there shall be not less than 4 rivets of finch diameter in each arm, while knees 40 inches deep require nine f-inch diameter rivets in each arm the number varies between these limits for stresses
these
;
knees of intermediate depths.
number
Obviously, only about half the will
be needed
for
of rivets required in bracket knees
welded knees of the same depth.
The depth and thickness of a beam knee varies with the depth of the beam, and the position of the latter in the ship. Generally, beams which form the top of a hold space are required of maximum depth, the distorting being greatest
stresses
Hence,
these places.
at
where there
in steamers
is
but
beam knees are of greater depth than if there were intermediate decks. The upper deck beam knees in vessels which have a range of wide-spaced beams below the upper deck, are to be of the scantlings of a single tier of beams, the
the knees of an upper
beam knees beams *of mentioned
of
without the
rigid
of her bulkheads,
depth
of
All
depth
beams
Rules
require
necessary
in
as
the
at
fitted
are
steamers
in
same lengths
very
one
where
tier
of
scantling
the
are
except
deck
tiers
Lloyd's
that
requirements
heads
all
similar
those
than
at
it
to
beams
steamers
extreme
In sailing ships,
be the same as
having
sailing
only one.
the
is
one
in
sailing
having
for
only.
tier
ships
one
tier
upper deck
may be be heavier
It
to
These
only.
vessels
have
no watertight
forward
end
they
;
are,
bulk-
therefore,
transverse stiffening which every steamer possesses in virtue and need the bracing given by beams of special strength and
knees.
beam knees should measure
of the
across the throats at least
^
of the
full
knee.
beams at every frame are to have plate moulded depth. Thus, in vessels 23 feet and under 24 feet depth, the knees are to be 33 inches x 33 inches and in vessels 26 feet and under 27 feet, 42 inches x 42 inches; the knees Deepening the knees for vessels of intermediate depths varying between these. strengthens the frames by shortening the unsupported length ; it also stiffens the vessel at the deck corners and arrests any tendency to change of form that might develop when the vessel is labouring among waves at sea. BALLAST TANKS. Nearly all modern cargo steamers are constructed to In large single-deck vessels the
bracket knees
varying in
size
with
the
—
load in
the
when
water-ballast
peak tanks, purpose.
steamer,
when
in
necessary, the water being carried in double bottoms,
deep tanks, or
Frequent^, it
is
all
these
in
some other space specially devised for are employed together in a single
methods
desired to be able to proceed to sea without using supple-
mentary stone or sand
ballast.
no
SHIP CONSTRUCTION are
tanks
Ballast
they have
long
not
voyages
usually
fitted
In their case, therefore, Another important reason for omitting first
cost.
Still,
in
sailing
ships,
as,
unlike
steamers,
and load and discharge comparatively rapid means of ballasting are of little use.
perform
to
seldom.
saving in
AND CALCULATIONS.
ballast
tanks" in
sailing
where there have been special reasons
ships
is
the
for so doing,
double bottoms, and even deep tanks, have been installed in sailing ships.
When devised
water began to be introduced as a means of ballasting, shipbuilders
many more
or less successful plans, to
economically carrying adopted. plating
From and
the
the
it,
first
tops
of
it
refer, for
now
generally
was seen that the broken space between the
the
suited for this purpose, since available for profitable
which we need not here
before they arrived at the efficient system
floors
in
the bottom of the
use could thus be
employment.
In the
made
shell-
ship was admirably
of space not otherwise
earliest vessels the tanks
were usually
only in one or two holds, and to obtain an adequate ballast capacity the tanks
Fig.
103.
Ill
BALLAST TANKS. reversed frames with plugs of wrought iron, the latter being tightly place
a-nd
carefully
caulked.
Neither of
very satisfactory, as the abrupt termination
weakness in the structure
at the bilges
ship, watertightness at the
margin was
;
of the
wedged
found
methods was
these
tanks gave rise to
to
into
be
decided
moreover, even with careful workman-
difficult to secure.
Both of these objections were eventually overcome by severing the main and reversed frames at the tank margin, and fitting a continuous bar directly on to the shell-plating, the loss of transverse strength being made good by
introducer,
its
the
to
This arrangement, known as the M'Intyre
tank top. of
on
substantial brackets from the frame bar
fitting
is,
in
principle,
the
margin plate of the
System
one now adopted
at
from the name
margin in
the
vessels having a ballast tank extending over the greater part of the length.
all
In
the earliest vessels built, on this system, the angle connecting the margin-plate to
the shell-plating was fitted inside the tank
to
the
tank-top
by an
angle
bar
now,
;
and the margin-plate connected margin-plate
the
is
flanged
at
the
104.
Fig.
FRAMED
REV.
FRAME CUT
CONTINUOUS W.T.ANGIE
top and the shell bar brought outside the tank, improvements which have led to
much
better workmanship.
Fig.
104 shows the improved M'Intyre System.
In constructing a ballast tank extending over a portion only of the length,
a point of importance breaks.
To
the
is
maintenance of the longitudinal strength at the
stop the tank structure abruptly at any point would accentuate the
In such cases the usual plan
weakness of sections lying immediately beyond. is
continue the keelsons of the part of the
to
bottom,
a
so
as
minimum
to
scarph the
scarph
of
three
latter
frame
for
some
spaces),
structure
clear
of the double
distance
(Lloyd's
Rules require
and
connect
them
to
to
the
longitudinal girders where practicable. It
tinuous,
very soon
and
came
to
be recognised that by making a
for the full length of a vessel, other
ballast
tank con-
advantages besides the import-
ant one of carrying water-ballast could be secured.
It
was seen, for instance,
by the tank top-plating would greatly increase a against foundering, in the event of grounding on a rocky bottom
that the double skin afforded vessel's safety
also that the material required for the construction of the tank, being at a con-
SHIP CONSTRUCTION
112
AND CALCULATIONS.
axis, would be very efficient in resisting These considerations led to the adoption of a continuous ballast tank in many vessels, and when later, the Board of Trade consented to measure the depth for tonnage in such cases to the inner bottom
siderable
from
distance
neutral
the
longitudinal structural stresses.
double bottom became the rule in cargo steamers. length tank brought immediate changes in the internal
plating, a fore-and-aft
The
of a
fitting
framing of
full
of the
part
this
hull.
was
It
now found
possible
reduce the
to
depth of the tank as compared with that of one extending over a part only of the length
;
made
but this
impracticable to follow the usual plan in building
it
of fitting longitudinal girders on top of ordinary floors,
came
of construction was introduced, and
to
and a Cellular System
be generally adopted.
There are two principal methods of constructing a double bottom on this The first consists of illustrated in figs. 105* and 106* respectively.
system,
and
longitudinal
girders
the
being connected to the inner and outer bottoms
girders
By Lloyd's Rules
spaced,
suitably
at
least
floorplates
one longitudinal girder
fitted
alternate
at
frames,
by angle
bars.
required in vessels under
is
whose breadth of tank amidships is under 28 feet, and two between 34 feet and 50 feet in breadth, whose breadth of tank amidships is between 28 and 36 feet. Sometimes the parts are flanged in breadth,
34
feet
in
vessels
although the cost is thus somewhat reduced, there being and less riveting, there is a loss in rigidity, for which reason flanged work here is not very common. In way of the engine space, owing to the great vibration there due to the working of the machinery, the floorplates are fitted at every frame and stiffened at their upper edges by double reversed bars floorplates must also occur at the boiler bearers. As a rule flanged work is not resorted to in this region.! Before and abaft the engine space, at those frames to which no floorplates are attached, brackets, which in medium-sized! vessels should be wide enougn at the head to take three rivets in the vertical flange of the intermediate reversed angles for 4 of angles,
lieu
fewer
parts
but
to
fit
;
the
vessel's
plate,
set
length
amidships,
are
fitted
to
the
centre
and
girder
binding these parts together and strengthening them to
resist
margin
the stresses
up by the action of the water ballast when the vessel is in motion among The reversed bars in way of these intermediate frames are riveted to
waves.
the tank top-plating, to Avhich they act as stiffeners
;
frequently, however, they
and the inner bottom slightly increased The side girders and floors are pierced with manholes
are dispensed with
to
all
effected.
parts
of
The
the
centre
tank,
girder
considerable
a is
does a kind of internal keel
;
saving
in
has,
therefore,
thickness in
lieu.
to give ready access
weight
more important than the it
in
being
others,
also
thus
forming as
heavier scantlings,
is
not
it
re-
duced by manholes except perhaps at the extreme ends, and is stiffened top and bottom by heavy double bars (see fig. 105). In the earliest vessels built on this plan, the longitudinals were continuous and the floors intercostal, the * Figures taken
from Lloyd's Rules.
t See Remarks on Stiffening of Double Bottom at Fore End, p. 116. X When the longitudinal number is 20,000 and above.
BALLAST TANKS. owing to
former,
elements in to
the
the
neutral
Nowadays,
strength.
being
axis,
usual
is
it
considerable
for
the
floors
be continuous and the girders intercostal, an arrangement leading to greater of construction
simplicity
longitudinal
be
from
distances
their
longitudinal
113
ample.
still
increase
the
in
An
—a
which,
strength,
most important point— and howe'ver,
in
modern
important advantage of the of
stiffness
obviously having greater
the
bottom,
the
and
rigidity
Fig.
105.
strength
some reduction show
to
calculations
vessels,
arrangement
latter
comparatively
than
long
in
to
a great
is
floorplates
short
girders.
fore-and-aft
SECTION AT INTERMEDIATE FRAME
PLAN £23"
-H-,.-^^. EL
*
BRACKET
£=H*J. SIDE GIRDERS
/*— 1 1
I
1
ft
LZ
CENTRE GWOtR
^^TfF""^
or
ti
When
longitudinals
elements as
in
order that their
impaired, the manholes through
and those
possible,
continuous,
are
may not be
in
different
girders
shifted
efficiency
as
strength
them should be as few
well
clear
of
each
other
transversely.
When vessels
the
inner bottom fig.
vessels exceed 400 feet, and in single-deck moulded depth, the above plan of framing the not considered adequate, and the second method, shown in
rule
lengths
which exceed 26
106,
is
of
feet
should be adopted.
In
this
case,
the floorplates are at every frame
SHIP CONSTRUCTION
ii 4
and continuous from centre girder
to
AND CALCULATIONS. margin plate on
one or two through the
girders have lightening holes,
each
The
except the centre one, are intercostal.
longitudinals,
while
side,
floorplates
floors into
each cellular
Fewer side girders required by this plan, only a single one being necessary on each side of centre if the ballast tank be under 36 feet in width and the breadth ship under 50 feet, and only two if the tank be under 48 feet and and one through every
space,
ship under 62 feet in breadth, larger vessels
the
girder
number being
the
girders with
of the
plate.
previous
case.
The
intercostals
Fig,
are
of the
approxi-
closer floors gives
and tank top-plating as attached to the floors and to the shell
106.
FLOOR AT EVERY -FRAME'
PLAN
inner and outer skins by riveted angle bars or flanges as being riveted to the frames
are the
proportionately increased in
the
same extent of unsupported area of
mately the in
the spacing
;
intercostal
the
and side
and
to angle bars
;
and the
floors,
as well
under the inner bottom plating,
have angle connections to the centre girder and the margin-plate; the centre girder attachments, consisting of double angles for half length amidships when the transverse
number reaches
or exceeds
66.
In the
latest
vessels
of this
size,
single
angle attachments between the floors and centre girder have sometimes been It is seen that as regards the inadopted, the flanges being double riveted. ternal framing of
somewhat increase
less
of
the inner bottom, the longitudinal strength in this last plan
is
than in the previous one, but in view of the tendency towards
breadth
in
modern
vessels,
demanding
considerable
transverse
and of the greatly enhanced stiffness of the bottom on account of the numerous deep floorplates, it would appear that the continuous floor on every frame method of construction is the better one, particularly as the strength,
"5
BALLAST TANKS.
absence of the bracket work required at the intermediate spaces in the previous plan renders the work of simpler construction. This arrangement is at anyrate a
favourite
smaller
the
when
plating
who have
frequently
in
much
Lloyd's
Rules
adopted size.
it
those
greater
shell-plating
tank,
the
the
builders,
requiring it owing to their strength of this plan over the previous one by allowing (except the flat keel and garboard strakes) in way of the
than
vessels
recognise
many
with
-52
to
exceeds
'66 '66
of an inch in thickness, to be slightly reduced;
of an inch in
Fig.
TANK. SIDE BRACKET
thickness,
107.
no reduction
is
when
allowed.
AND CALCULATIONS.
SHIP CONSTRUCTION
Il6
and depth,
increase in breadth
some
pose, over
the
end
fore
angles
growth
with
the
tank
margin,
of
which
in
in
additional
vessels
by
provided
is
moderate
of
vessels
Besides
size.
becomes
strength
gusset-plates
fitting
sketches of these arrangements angles
or
Irame, according the
to
are
fitted
the vessel's
number and
transverse
are
shown every
at size,
the
in
figs.
fifth,
the limits
value
of
d,
the
105,
being fixed the
vessel's
foregoing,
tops
at
the
of
the
Detailed
results.
and
106,
These
107.
second or single
fourth, third,
i.e.,
pur-
In recent instances,
good
angles have been substituted for the gusset-plates with
the
necessary
to
wing brackets and to the sides of the tank top-plating.
gusset-plates
this
and Lloyd's Rules
respect,
this
for
Experience has shown
from the collision bulkhead to one-fourth the
stem
the
attention
special
require
to
from
double bars or equivalent
become necessary
quickly
portion at least of the vessel's length.
demand double length
particularly the latter,
double-riveted flanges
single bars with
in
length
each
case by
unsupported
of
frame.
The
little comment. Lloyd's be arranged in longitudinal strakes and the butts shifted well clear of each other and of those of the longitndinal girders, when these are continuous, and this is usually done. In some districts, notably the N.E. coast, transverse strips have been fitted under the watertight bulkheads to allow the building of the latter to be proceeded with at an early stage of the
fitting
of the inner bottom plating calls for
Rules recommend that
it
packing pieces, inner bottom plating
To
commended.
work, but the system cannot be otherwise
sometimes joggled
is
save the fitting of
seams, but
the
at
been raised to the depression thus caused in the surface, as forming lodgments for water, particularly where ceiling is laid, rapid corrosion objection has
resulting this
space
reduced
is
give
to
corrosion
Like other longitudinal material, the
consequence.
in
plating
the ends;
at
additional
more
but
strength,
which takes place
increased
is
it
in
thickness
of
way of the machinery
particularly
allow
to
for
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