Department of Naval Architecture & Ocean Engg, IMU , M.Tech(NA&OE), Batch- I MIDSHIP SECTION INTRODUCTION Midship section design is in accordance with Part 4, Chapter 9 of “Lloyd’s Register”, Rules and Regulations for Classification of Ships, which has been revised to include requirements for Double Hull Oil Tankers. These requirements reflect regulation 13F of Annex I of MARPOL 73/78 with the other features. Fig.1 is a typical midship section of a double skin tanker. Figure 1 - Typical midship section of a double skin tanker 1.1. Definitions (1) L : Rule length, in m, is the distance, in meters, on the summer load water line from the forward side of the stem to the after side of the rudderpost or to the center of the rudder stock, if there is no rudder post. L is neither to be less than 96% nor to be greater than 97% of the extreme length on the summer load water line.
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Department of Naval Architecture & Ocean Engg, IMU , M.Tech(NA&OE), Batch- I
MIDSHIP SECTION INTRODUCTION
Midship section design is in accordance with Part 4, Chapter 9 of “Lloyd’s Register”,
Rules and Regulations for Classification of Ships, which has been revised to include requirements
for Double Hull Oil Tankers. These requirements reflect regulation 13F of Annex I of MARPOL
73/78 with the other features. Fig.1 is a typical midship section of a double skin tanker.
Figure 1 - Typical midship section of a double skin tanker
1.1. Definitions
(1) L : Rule length, in m, is the distance, in meters, on the summer load water line
from the forward side of the stem to the after side of the rudderpost or to
the center of the rudder stock, if there is no rudder post. L is neither to be
less than 96% nor to be greater than 97% of the extreme length on the
summer load water line.
97% of extreme length of LWL = 229.89m
(2) B : Breadth at amidships or greatest breadth, in meters.
B = 42.0 m
(3) D : Depth is measured, in meters, at the middle of the length L, from top of the keel
to top of the deck beam at side on the uppermost continuous deck.
D = 22.0 m
(4) T : T is the summer load draught in m, measured from top of keel.
T = 14 m
Department of Naval Architecture & Ocean Engg, IMU , M.Tech(NA&OE), Batch- I
(5) LPP : Distance in m on the summer LWL from foreside of the stem to after side
of rudder post, or to the center of the rudder stock, if there is no rudder post.
LPP = 233 m
(6) CB : Moulded block coefficient at draught T corresponding to summer
waterline, based on rule length L and moulded breadth B, as follows:
CB =
(7) B : The width of plating supported by the primary member or secondary
member in m or mm respectively.
(8) be : The effective width, in m, of end brackets.
(9) bI : The minimum distance from side shell to the inner hull or outer
longitudinal bulkhead measured inboard at right angles to the centre line
at summer load water line, in m
(10) le : Effective length, in m, of the primary or secondary member, measured
between effective span points.
(11) ds : The distance, in m, between the cargo tank boundary and the moulded
line of the side shell plating.
(12) h : The load height applied to the item under consideration, in m.
(13) db : The distance, in m, between the bottom of the cargo tanks and the
moulded line of the bottom shell plating measured at right angles to the
bottom shell plating.
(14) kL, k : Higher tensile steel factors. For mild steel, kL, k may be taken as 1.
(15) I : Moment of inertia, in cm3, of the primary or secondary member, in
association with an effective width of attached plating.
(16) s : Spacing of secondary members, in mm.
(17) S : Overall span of frame, in mm
(18) t : Thickness of plating, in mm.
(19) Z : Section modulus, in cm3, of the primary or secondary member, in
association with an effective width of attached plating.
(20) L1 : Length of ship in meters, but need not be greater than 190m.
(21) CW : Wave head, in m.
(22) RB : Bilge radius, in mm.
moulded displacement (m3) at draught T
L.B.T
Department of Naval Architecture & Ocean Engg, IMU , M.Tech(NA&OE), Batch- I
(23) FD,FB : Local scantling reduction factor above neutral axis and below neutral axis
respectively. FD = 0.67, for plating and 0.75, for longitudinals
FB = 0.67, for plating and 0.75, for longitudinals
(24) O : Specified minimum yield stress, in N/mm2
(25) C : Maximum compressive hull vertical bending stress, in N/mm2
(26) T1 : T but to be taken not less than 0.05L m
= 11.495 m
(27) hT1 : T + CW m but need not be taken greater than 1.36 T
(28) hT2 : T + 0.5CW m but need not be taken greater than 1.2 T
(29) c1 : 60 / (225 – 165 FD) at deck; 1.0 at D/2; 75 / (225 – 150FB) at base ` line
of ship
(30) c2 : 165 / (345 – 180FB) at deck; 1.0 at D/2; 165/(345 – 180FB) at base line of
ship
(31) R : sin, where is the roll angle in degrees
sin = (0.45+0.1 L/B)(0.54 – L/1270)
R =0 .358
(32) D1 : D, in m, but is to be taken not 10 and need not be taken 16
D1 = 16m
sin = (0.45 + 0.1L/B)(0.54 – L / 1270 )
R = 0.358
(33) dDB : Rule depth of center girder, in mm
(34) SS : Span of the vertical web, in m
(35) tW : Thickness of web, in mm
(36) tB : Thickness of end bracket plating, in mm
1.1.2. Class Notation
Vessel is designed to be classed as ‘100 A1 Double Hull Oil Tanker ESP.’ ESP means
Enhanced Survey Program. This is for seagoing tanker having integral cargo tanks for carriage of oil
having flash point > 60o C.
1.1.3. Cargo Tank Boundary Requirements
Minimum double side width (ds) in m
Department of Naval Architecture & Ocean Engg, IMU , M.Tech(NA&OE), Batch- I
ds = 0.5 + (dwt/20,000) or ds = 2.0 m
whichever is lesser. But ds should not be less than 1 m.
ds = 0.5+(95,000/20,000) = 5.25 m
Double side width is taken as 2.0 m to get the required ballast volume.
ds = 2.0 m
Minimum double bottom depth (dB)
dB = B/15 or dB = 2.0 m
whichever is lesser
dB = 42/15 = 2.8 m
A double bottom height of 2.0 m is provided to get the required ballast volume.
dB = 2.0 m
Structural configuration adopted has a single centerline longitudinal bulkhead. According
to Maritime Law of India (Appendix V111:63, Regulation 24), Length of cargo hold shall not exceed
10m or (0.25bi /B +0.15) x LL (for longitudinal bulkhead provided at centerline), whichever is greater.
[LRS Part 4, Chapter 9, Section 1.3.9]
(0.25bi /B +0.15) LL = 35.85 m
For length of cargo tanks and tank boundaries refer General Arrangement Plan.
Type Of Framing System
The bottom shell, inner bottom and deck are longitudinally framed (for L > 75m). The
side shell, inner hull bulkheads and long bulkheads are also longitudinally framed (L > 150m). When
the side shell in long framed, the inner hull bulkhead is also to be framed longitudinally. Primary
members are defined as girders, floors, transverses and other supporting members.
LONGITUDINAL STRENGTH
Design vertical wave bending moment (P3, C4, S5.2)
The appropriate hogging or sagging design hull vertical wave bending moment at
amidships is given by the following:
M w = f1 f2 Mwo
Where,
Department of Naval Architecture & Ocean Engg, IMU , M.Tech(NA&OE), Batch- I
M wo = 0.1C1 C2 L2 B (C b + 0,7) kN m
Cb is to be taken not less than 0,60
C1 is given in Table 4.5.1 = 10.163
C2 = 1, (also defined in 5.2.2 at other positions along the length L)
f1 = ship service factor. For unrestricted sea-going service f 1 = 1,0