Section
4 Hull envelope plating
4.1 General
4.1.2 For
requirements in respect of structural details, bilge keels, attachments,
etc. see
Pt 3, Ch 10 Welding and Structural Details.
In addition the ShipRight FDA Procedure, Structural Detail Design
Guide (SDDG), indicates recommended structural design configurations
for double hull tanker structural details to assess and improve the
relative fatigue life performance of the details in critical areas.
4.2 Symbols
4.2.1 The
symbols used in this Section are defined as follows:
|
F
M
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= |
the greater of F
D or F
B
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s
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= |
spacing,
in mm, of longitudinals or transverse frames. Except where indicated
in the text, s is not to be taken less than:
|
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C
w
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= |
a wave head, in metres |
|
|
= |
7,71 × 10−2
L e−0,0044L
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where
|
e |
= |
base of natural
logarithms 2,7183 |
|
R
B
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= |
bilge radius, in mm, as defined in Table 1.5.2 Bottom shell and bilge
plating in Pt 4, Ch 1 General Cargo Ships
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|
S
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= |
overall
span of frame, in mm, measured between deck and bottom support points
or to, or between, stringers, where fitted |
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T
1
|
= |
T but to be taken not less than 0,05L m
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|
α |
= |
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|
σc |
= |
maximum compressive hull vertical bending stress, in
N/mm2 given by σD and σB as defined in Pt 3, Ch 4, 5.6 Permissible hull vertical bending stresses 5.6.1 as appropriate |
| = |
For ships of normal design, not exceeding
90 metres in length, the value of maximum compressive hull vertical
bending stress may be determined as follows: |
| = |
at strength deck |
|
|
= |
|
|
|
= |
at keel |
|
|
= |
|
|
|
= |
where Z
min, Z
D, Z
B and σ are in accordance with Pt 3, Ch 4, 5 Hull bending strength
|
|
σo
|
= |
specified minimum yield stress, in N/mm2
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|
h
T1
|
= |
T + C
w m but need not be
taken greater than 1,36T
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|
h
T2 |
= |
T + 0,5C
w m but need not
be taken greater than 1,2T
|
| = |
For longitudinally framed bottom and bilge
plating T is to be taken as T
1
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Other symbols are defined in Pt 4, Ch 9, 1.5 General definitions and symbols.
Table 9.4.1 Hull envelope plating - minimum
thickness, in mm
| Longitudinally framed
|
Item
|
Item
No. see Fig. 9.4.1
|
Transversely framed,
see
Pt 4, Ch 9, 1.3 Class notation and applicable Rules for CSR Double Hull Oil Tankers for limits of application
|
see Note 1
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Deck
|
1
|
see
Pt 4, Ch 9, 1.3 Class notation and applicable Rules for CSR Double Hull Oil Tankers
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or
whichever is the greater see Note
1
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Sheerstrake and gunwale
|
2
|
see Note 6
or
whichever is the greater see Note
1
|
see Notes 6 and 7
or
whichever is the greater see Note 1
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Side shell
above mid-depth
|
3
|
see Notes 6 & 7
or
whichever is the greater see Note
1
|
| 4
|
see Notes 6 and 7
or
whichever is the greater see Note
1
|
|
|
Side shell below mid-depth
|
5
|
see Notes 6 and 7
But not less than:
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(a)  at mid-depth
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Intermediate thickness by interpolation
|
6
|
see Notes 2, 6 and 7
or
whichever is the greater see Note 1
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(b) 
at upper turn of bilge See Notes 1 and 2
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Intermediate thickness by interpolation
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or
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Bilge
(see Note 4)
|
7
|
see Notes 6 and 7
or
whichever is the greater see Note
1
|
| whichever is the greater
see Note 1
|
Bottom
shell
|
8
|
see
Pt 4, Ch 9, 1.3 Class notation and applicable Rules for CSR Double Hull Oil Tankers
|
As for
item 8, +2mm, but need not exceed
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Keel
|
9
|
|
|
Note
2. The thickness of side shell plating
need not exceed that which would be required for the bottom shell
using the spacing of the side shell longitudinals.
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|
|
|
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Note
5. Keel thickness is in no case to be
less than that of the adjacent bottom shell plating.
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Note
6. Where separate maximum sagging and
hogging still water bending moments are assigned, F
D may be based on the sagging moment and F
B on the hogging moment.
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|
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4.3 Deck plating
4.3.1 The
midship thickness of deck plating is to be maintained for 0,4L amidships
and tapered outside this region in association with the deck longitudinals
in accordance with Pt 4, Ch 9, 5.5 Deck longitudinals outside 0,4L amidships. The
midship thickness may, however, be required over an increased extent
if it is shown to be necessary by the bending moment curves. Where
partial filling of the tanks is contemplated the deck plating is also
to comply with the requirements of Pt 4, Ch 9, 6.1 General 6.1.2.
4.3.2 For
ships not exceeding 200 m in length, the deck thickness outside 0,4L amidships is to be not less than  at any point within the cargo tank region. For lengths
of 250 m and over, the thickness is to be not less than  . Intermediate values are to be obtained by interpolation.
For the purpose of this paragraph, the minimum value of s given
in Pt 4, Ch 9, 4.2 Symbols 4.2.1 is not to be applied.
4.3.3 The
plating thickness outside 0,4L amidships is to be not
less than:
4.4 Sheerstrake
4.4.1 The
midship sheerstrake thickness is to be maintained for 0,4L amidships
and tapered outside this region as provided for in Pt 3, Ch 5 Fore End Structure and Pt 3, Ch 6 Aft End Structure. In the taper region, however, the sheerstrake thickness
need not exceed the adjacent deck or shell thickness, whichever is
the greater.
4.4.3 Where
a rounded sheerstrake is incorporated, the radius is not, in general,
to be less than 15 times the thickness. The radius is to be made by
careful cold rolling or bending.
4.5 Shell plating
4.5.1 The
midship thicknesses of side and bottom shell plating are to be maintained
for 0,4L amidships and tapered outside this region as
provided for in Pt 3, Ch 5 Fore End Structure and Pt 3, Ch 6 Aft End Structure. The midship thicknesses may be required
over an increased extent if it is shown to be necessary by the bending
moment or shear force curves.
4.6 Bilge plating
4.6.3 Where
bilge longitudinals are omitted, the plating thickness outside 0,4L amidships will be considered in relation to the support derived
from the hull form and internal stiffening arrangements. Due regard
will be taken of the possibility of increased loading in the forward
region.
4.7 Keel
4.7.2 The
width of the keel over the cargo tank region is to be not less than:
70B mm but need not exceed 1800 mm and is to be
not less than 750 mm.
4.8 Taper of higher tensile steel
4.9 Thicknesses at ends of erections
4.9.1 The
deck plating thickness at the poop front is to extend into the poop
for a distance at least equal to one-third of the breadth, B.
4.9.2 If the
poop front extends to within 0,25L of amidships, the
sheerstrake and the stringer plate at the break are to be increased
by 20 per cent. No increase is required if the poop front is 0,3L from
amidships or greater. The increase at intermediate lengths is to be
obtained by interpolation and is to be applied to the tapered thickness
of the sheerstrake and stringer plate.
4.9.3 Where
the poop extends to within 0,3L of amidships and the
enclosed machinery opening extends to within  of the poop front and has a width exceeding one half
of the breadth of the ship at the poop front, the thickness of deck
plating may require to be increased. The forward corners of the casing
opening are to be well rounded.
4.10 Deck openings
4.10.1 Openings
in the deck are to be kept to the minimum number consistent with operational
requirements.
4.10.2 Plate
panels in which openings are cut are to be adequately stiffened, where
necessary, against compression and shear buckling.
4.10.3 The
corners of all openings are to be well rounded, and the edges smooth.
4.10.4 Where
the stress concentration factor in way of the opening exceeds 2,4,
edge reinforcement is generally to be fitted. This is normally to
be in the form of a spigot of adequate dimensions, but alternative
arrangements will be considered.
4.10.5 Alternatively,
the shape of the opening is to be such that a stress concentration
factor of 2,4 is not exceeded.
4.10.6 In
this respect, reinforcement will not, in general, be required in way
of:
-
elliptical openings
having their major axis fore and aft and ratios of length to breadth
not less than 2 to 1, or
-
openings of other
shapes, provided it has been shown by suitable tests that the stress
concentration factor does not exceed 2,4.
4.10.7 Circular
openings of diameter up to 325 mm will also be accepted, provided
that they are situated at such a distance from any other opening that
there is an intervening width of plating of not less than five times
the diameter of the smaller of the two openings.
4.10.9 Where
a deck longitudinal is cut in way of an opening, within 0,4L amidships,
compensation is to be arranged to ensure full continuity of area.
4.10.10 The
area of any edge reinforcement which may be required is not to be
taken into account in determining the required sectional area of compensation
unless such reinforcement is designed to absorb the loadings from
cut longitudinals in way of opening.
4.10.11 Increased
scantlings and/or compensation may also be required for large openings
outside 0,5L amidships, or where openings are close to
breaks of superstructure or other areas of high stress in any location
on the ship.
4.10.12 Where
small diameter threaded openings for staging wires are arranged on
the upper deck, they are to be located clear of the other openings
and similar areas of stress concentration. Care is to be taken to
ensure a gradual transition at the thread ends and the edges of the
holes are to be smooth. The closing arrangements are to be as required
by Pt 4, Ch 9, 13 Access arrangements and closing appliances.
4.11 Shell openings
4.11.1 Sea
inlets in pump-rooms situated within 0,4L amidships,
are, if practicable, to be fitted clear of the bilge radius. All openings
are to be arranged so as to minimise discontinuity of transverse frames,
longitudinals or bilge keels. Compensation is to be provided for all
openings within 0,4L amidships and may also be required
for openings in the vicinity of the poop front. The compensation should,
if possible, take the form of an insert plate rather than a doubler.
4.11.2 If
openings are not circular or oval, the corners are to be rounded with
as large a radius as practicable.
4.12 Superstructures
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