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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.

(4)

D

= 22.0 m

T

:

T

= 14 m

T is the summer load draught in m, measured from top of keel.

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.

(6)

LPP

= 233 m

CB

:

Moulded

block

coefficient

at

draught

T

corresponding

to

summer

waterline, based on rule length L and moulded breadth B, as follows: moulded displacement (m3) at draught T CB

= L.B.T

(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

longitudinal

distance

bulkhead

from

measured

side

shell

to

inboard

at

right

the

inner

angles

hull

to

the

or

outer

centre

line

at summer load water line, in m (10)

le

:

Effective

length,

in

m,

of

the

primary

or

secondary

member,

cargo

tank

boundary

and

measured

between effective span points. (11)

ds

:

The

distance,

in

m,

between

the

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,

moulded

line

in of

m, the

between bottom

the shell

bottom plating

of

the

measured

cargo at

tanks

right

angles

and

the

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

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

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.

Department of Naval Architecture & Ocean Engg, IMU , M.Tech(NA&OE), Batch- I

(23)

FD,FB :

Local

scantling

respectively.

reduction

factor

above

neutral

axis

FD

= 0.67, for plating and 0.75, for longitudinals

FB

= 0.67, for plating and 0.75, for longitudinals

(24)

σO

:

Specified minimum yield stress, in N/mm2

(25)

σC

:

Maximum compressive hull vertical bending stress, in N/mm2

(26)

T1

:

T but to be taken not less than 0.05L m

and

below

neutral

axis

= 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

:

sinθ, where θ is the roll angle in degrees sinθ R

(32)

D1

:

= (0.45+0.1 L/B)(0.54 – L/1270) =0 .358

D, in m, but is to be taken not < 10 and need not be taken >16 D1 = 16m sinθ = (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: Mw Where,

=

f1 f2 Mwo

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

f2

=

–1,1 for sagging (negative) moment

f2

=

for hogging (positive) moment

=

1.025

=

0.1×10.163×1×(229.89) 2×42×(.825+0.7)

=

3440180.424 KNm

=

1×-1.1×3440180.424 =-3784198.47

=

1×1.025×3440180.424 =3526184.935

1.9C b

M wo

Mw

(C b + 0.7)

(sagging) (hogging)

Permissible Still water Bending Moment Ms

=

fsn×Cw×L2×B×(CB+0.7) KNm

fsn

=

0.072

Cw

=

10.75-{(300-L)/100}3/2

Ms

=

0.072×10.163×(229.89)2×42×(0.825+0.7)

=

247692.991 KNm

for sagging bending moment

Hull Moment of Inertia

(P3, C4, S5. 8) (| M s + M w |)

Imin

=

3L

=

139.373 m4

kL×σ

10 –5 m4

Minimum Hull Section Modulus [LRS Part 3, Chapter 4, Section 5]

The hull midship section modulus about the transverse neutral axis, at the deck or keel is to be not less than Z min

=

f1KL C1L2B (CB + 0.7) x 10-6 m3

Department of Naval Architecture & Ocean Engg, IMU , M.Tech(NA&OE), Batch- I

f1

=

ship’s the

service service

factor.

restriction

T and

be in

any

specially event

For unrestricted sea going service f1 = 1.0 ∴f1 taken as 1 For M.S; KL

=

1 [Part 3 Chap.2 Sec 1.2]

C1

=

10.75 – [(300-L)/100] 1.5 for 90