Midship

Department of Ship technology, CUSAT, B.Tech (NA&SB, Batch - XXVII

CHAPTER 8 MIDSHIP SECTION DESIGN

182


MIDSHIP SECTION 8.1 INTRODUCTION Midship section design is in accordance with Ice class Rules given by Finnish Maritime Administration, Sept 2003 and the rules for classification of ships given by Lloyd’s Registrar of Shipping July 2001. Fig. 8.1 is a typical midship section of a double skin ice class tanker.

Figure 8.1 - Typical midship section of a double skin Ice class Tanker 8.1.1. 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 = 264.39 m

(2)

B

: Breadth at amidships or greatest breadth, in meters. B = 48.7 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

= 23.76 m

(4)

T

: T is the Maximum Ice Class draught of the ship, in m = 16.75 m

(5)

LPP

: Distance in m on the summer LWL from foreside of the stem to after side of rudder post, or to the centre of the Podded unit, if there is no rudder post.

(6)

LPP = 263.00 m LPAR = Length of parallel midship body, in m (approx. 92.05 m)

(7)

CB

: Moulded block coefficient at draught T corresponding to summer waterline, based on rule length L and moulded breadth B, as follows: 183


CB (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19)

Moulded displacement (m3) at draught T = 0.84

hG = h = Awf = α = φ1 = φ2 = DP = HM = HB = ReH = LWL = BWL =

Ice thickness, in m, defined in the table given by FSICR 1 Area of the waterline of the bow in m2. Angle of the waterline at B/4 = 70 Rake of the Ice breaking stern at the centreline = 24.2 Rake of the Ice breaking stern at B/4 = 24.5 Diameter of propeller = 7260 mm Thickness of the brash ice in mid channel, in m = 1.0 m Thickness of the brash ice layer displaced by the stern Minimum yield stress, in N/mm2, of the material defined Load Waterline, at fully loaded condition. Ballast Waterline at Ballast condition.

(20) b

: The width of plating supported by the primary member or secondary member in m or mm respectively.

(21) be

: The effective width, in m, of end brackets.

(22) 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.

(23) le

: Effective length, in m, of the primary or secondary member, measured between effective span points.

(24) ds

: The distance, in m, between the cargo tank boundary and the moulded line of the side shell plating.

(25) 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.

(26) k : Higher tensile steel factors. For HT steels (Lloyd’s AH32, DH32 & EH32), k = 0.78 (27) s

: Spacing in m of ordinary stiffeners or primary support as applicable.

(28) S

: Overall span of frame, in mm

(29) t

: Thickness of plating, in mm.

(30) Z

: Section modulus, in cm3, of the primary or secondary member, in association with an effective width of attached plating.

(31) RB

: Bilge radius, in mm.

(32) 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

(33) dDB : Rule depth of center girder, in mm 184


(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

8.1.2 Class Notation Vessel is designed to be classed as ‘+100 A1(ice) Double Hull Oil Tanker ESP.’ ESP means Enhanced Survey Program. This is for Ice navigating tanker having integral cargo tanks for carriage of oil having flash point > 60o C. Where the length of the ship is greater than 190m, the scantlings of the primary supporting structure are to be assessed by direct calculation and the Ship Right notations Structural Design Assessment (SDA), Fatigue Design Assessment (FDA) and Construction Monitory (CM) are mandatory. 8.1.3 Cargo Tank Boundary Requirements Minimum double side width (ds) 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 + (150000/20,000) = 8.0 m

Double side width is taken as 2.8 m to get the required ballast volume. ∴ ds

=

3.0 m

Minimum double bottom depth (dB) dB

=

B/15 or dB = 2.0 m

Whichever is lesser dB

= 48.76/15 = 3.25 m

A double bottom height of 3.0 m is provided to get the required ballast volume. ∴ dB

=

3.0 m

Structural configuration adopted has a single centreline longitudinal bulkhead. For length of cargo tanks and tank boundaries refer General Arrangement Plan. 8.1.4 Type Of Framing System [LRS Part 4, Chapter 9, Section 1.3.10, 1.3.11] 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.

185


8.2 LONGITUDINAL STRENGTH 8.2.1 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

f1

=

ship’s service factor, specially considered depending upon the service restriction and in any event should not be less than 0.5 For unrestricted sea going service f1 = 1.0

∴f1 taken as 1 and KL = 0.78 (Grade DH32/EH32) =

10.75 – [(300-L)/100] 1.5 for 90
=

10.537

CB

=

Block Coefficient = 0.84

∴ Zmin

=

43.09 m3

C1

8.2.2 Hull Envelope Plating

1. Deck plating 2. Sheer strake and shell plating above Ice strengthened region. 3. Ice strengthened shell 4. Side shell below ice strengthening 5. Bilge 6. Bottom shell 7. Keel

Fig. 8.2 Itemization of parts

186


For longitudinally framed system the web structure:

Fig 8.3 Framing system 8.2.3 Minimum require Power (R / 1000)3 / 2 [kW] ; P = K e CH DP Table 8.1 Values of Ka

Propeller type or machinery 1 propeller 2 propellers 3 propellers

CP or electric or hydraulic propulsion machinery 2.03 1.44 1.18

FP propeller 2.26 1.60 1.31

Ke = 1.60 RCH is the resistance in Newton of the ship in a channel with brash ice and a consolidated layer: 3

⎛ LT ⎞ A 2 R CH = C1 + C 2 + C 3C μ (H F + H M ) (B + C ψ H F ) + C 4 L PAR H 2F + C5 ⎜ 2 ⎟ wf ⎝B ⎠ L Cμ = 0.15cosϕ2 + sinψsinα = 0..546 Cμ is to be taken equal or larger than 0.45

C ψ = 0.047 ⋅ψ − 2.115, and C ψ = 0 if ψ ≤ 45° ⎛ tanϕ 2 ⎞ o ⎟ = 30.17 ⎝ sinα ⎠

ψ = arctan ⎜

187


C ψ = 25.89 HF = 0.26 + (HMB)0.5 = 7.2 m HM = = = HM =

1.0 for ice classes IA and IA Super 0.8 for ice class IB 0.6 for ice class IC 1.0

C1 and C2 take into account a consolidated upper layer of the brash ice and are to be taken as zero for ice classes IA, IB and IC. For a ship with a bulbous bow, ϕ1 shall be taken as 90°. Given: C3 = 845 kg/(m2s2) C4 = 42 kg/(m2s2) C5 = 825 kg/s2 3

⎛ LT ⎞ 5 ≤ ⎜ 2 ⎟ ≤ 20 ⎝B ⎠ P = 21.2 MW (approx)

8.2.4 Ice load Height of load area An ice-strengthened ship is assumed to operate in open sea conditions corresponding to a level ice thickness not exceeding ho. The design height (h) of the area actually under ice pressure at any particular point of time is, however, assumed to be only a fraction of the ice thickness. The values for ho and h are given in the following table. Table 8.2 Values of ho and h Ice Class IA Super IA IB IC

ho [m] 1.0 0.8 0.6 0.4

h [m] 0.35 0.30 0.25 0.22

8.2.5 Ice pressure

The design ice pressure is determined by the formula: p = cd · c1 · ca · po [MPa], where

188


= a factor which takes account of the influence of the size and engine output of cd the ship. It is calculated by the formula: cd =

a⋅k + b 1000

k=

Δ⋅P 1000

a and b are given in the following table: Table 8.3 Values of a and b

a b

Region Forward Midship & Aft k ≤ 12 k > 12 k ≤ 12 k > 12 30 6 8 2 230 518 214 286

Δ P

= the displacement of the ship at maximum ice class draught [t] = 183376.12 t = the actual continuous engine output of the ship [kW] 38250 KW K = 83.75 a =2 b = 286 = a factor which takes account of the probability that the design ice pressure c1 occurs in a certain region of the hull for the ice class in question. The value of c1 is given in the following table: Table 8.4 values of c1

189


Table 8.4 values of c1 Ice Class Forward 1.0 1.0 1.0 1.0

IA Super IA IB IC

Region Midship 1.0 0.85 0.70 0.50

Aft 0.75 0.65 0.45 0.25

c1 = 1 = a factor which takes account of the probability that the full length of the area ca under consideration will be under pressure at the same time. It is calculated by the formula: 47 - 5 l a ; maximum 1.0 ; minimum 0.6 ca = 44

la shall be taken as follows: Table 8.5 Values of la Structure Shell Frames

Type of framing Transverse Longitudinal Transverse Longitudinal

Ice stringer Web frame

la [m] Frame spacing 2 ⋅ frame spacing Frame spacing Span of frame Span of stringer 2 ⋅ web frame spacing

la [m] 0.35 0.7 0.35 4.25 4.25 8.5

po = the nominal ice pressure; the value 5.6 Mpa shall be used.

8.3 Calculations for Ice strengthened part 8.3.1 Vertical extension of Ice Belt The vertical extension of the ice belt shall be as follows: Ice Belt is from 7.00 m to 17.35 ma long d ship’s depth from keel.

Table 8.6 Extension of Ice strengthening at midship Ice Class

Above LWL [m]

Below BWL [m]

IA Super IA IB IC

0.6 0.5 0.4 0.4

0.75 0.6 0.5 0.5 190

Ca [m] 1.028 0.989 1.028 0.585 0.585 0.102

P 2.612 2.511 2.612 1.486 1.486 0.260


8.3.2 Plate thickness in the ice belt For transverse framing the thickness of the shell plating shall be determined by the t = 667 s

f1 ⋅ p PL

σy

+ t c [mm]

formula: For longitudinal framing the thickness of the shell plating shall be determined by the formula:

t = 667 s

p PL f 2 ⋅σ

+ t c [mm ] y

S

= the frame spacing [m]

pPL

= 0.75 p [MPa]

p

= 1.88

f1

= 1.3 −

4.2 ; maximum 1.0 (h/s + 1.8) 2

= 0.764 0.4 ; when h/s ≤ 1 (h/s)

f2

= 0.6 +

f2

= 1.4 - 0.4 (h/s); when 1≤ h/s < 1.8 = 1.0

h

= 0.35

σy

= yield stress of the material [N/mm2]

σy

= 235 N/mm2 for normal-strength hull structural steel

σy

= 315 N/mm2 or higher for high-strength hull structural steel

If steels with different yield stress are used, the actual values may be substituted for the above ones if accepted by the classification society. tc = increment for abrasion and corrosion [mm]; normally tc shall be 2 mm t = 20.05 mm Taken t = 24 mm

191


Table 8.7 Vertical extension of ice strengthening Ice Class

Region

Above LWL [m]

From stem to 0.3L abaft it

1.2

Below BWL [m] To double bottom or below top of floors

IA Super Abaft 0.3L from stem

1.2

1.6

1.2 1.2

1.6 1.2

1.0

1.6

Abaft 0.3L from stem

1.0

1.3

Midship Aft

1.0 1.0

1.3 1.0

midship aft From stem to 0.3L abaft it IA, IB, IC

The vertical extension of the ice strengthening of the framing shall be at least as Vertical extension of ice strengthening in framing is from 5.41 m to 18.55 m. 8.3.3 Transverse frames

Section modulus The section modulus of a main or intermediate transverse frame shall be calculated by

[ ]

p⋅s⋅h ⋅l 6 10 cm 3 mt ⋅σ y the formula: p = ice pressure Z=

s

= frame spacing [m]

h

= height of load area

l

= span of the frame [m] 7 mo = 7 - 5h/l = yield stress [N/mm2]

mt σy

192


mo

= values are given in the following table:

Table 8.8 Values of mo

Z = 580.4 cm3 8.3.4 Longitudinal frames

The section modulus of a longitudinal frame shall be calculated by the formula: Z=

f3 ⋅f4 ⋅p⋅ h ⋅l 2 6 10 cm 3 m ⋅σ y

[ ]

The shear area of a longitudinal frame shall be: A=

3 ⋅f3 ⋅ p ⋅ h ⋅l 4 10 cm 2 2σ y

[

]

This formula is valid only if the longitudinal frame is attached to supporting structure by brackets 193


f3

= factor which takes account of the load distribution to adjacent frames f3 = (1 - 0.2 h/s) = 0.8.

f4

= factor which takes account of the concentration of load to the point of support, f4 = 0.6

p

= ice pressure

h

= height of load area

s

= frame spacing [m]

l

= span of frame [m]

m

= boundary condition factor; m = 13.3 for a continuous beam; where the boundary conditions deviate significantly from those of a continuous beam, e.g. in an end field, a smaller boundary factor may be required.

σy

= yield stress

Z

= 1076.5 cm3

A

= 48.62 cm2

Scantling selected 330x15 HB A = 65.9 cm2

8.3.5 Stringers within the ice belt

The section modulus of a stringer situated within the ice belt (see 4.3.1) shall be calculated by the formula: f ⋅ p ⋅ h ⋅l 2 6 Z= 5 10 cm 3 m ⋅σ y The shear area shall be:

[ ]

A=

[ ]

3 ⋅ f5 ⋅ p ⋅ h ⋅ l 4 10 cm 2 2σ y

The product p ⋅ h shall not be taken as less than 0.30. f5

= factor which takes account of the distribution of load to the transverse frames; to be taken as 0.9

σy

= yield stress

Z

= 2153 cm3

A

= 53.34 cm2

194


8.3.6 Load on Web frames in Ice Belt

The load transferred to a web frame from an ice stringer or from longitudinal framing shall be calculated by the formula: F = p ⋅ h ⋅ S [MN] The product p ⋅ h shall not be taken as less than 0.30 S

= distance between web frames [m]

F

= 0.76 MN

8.4 Dimensions of non Ice strengthened parts: 8.4.1 Deck plating: [Design Ice class and steel grade, RS]

t = 20 mm For Lloyd’s grade DH32, and for Russian Ice class LU4 or FMA Ice class 1A. 8.4.2

Sheer strake: [Design Ice class and steel grade, RS]

t = 20 mm For Lloyd’s grade EH32, and for Russian Ice class LU4 or FMA Ice class 1A. 8.4.3 Side shell below Ice strengthening:

The greatest of the following is to be taken: t = 0.001s (0.059L1 + 7) √ FB/kL = 11.81 mm But not less than t = 0.0042 s√ hT1k s = spacing of shell longitudinals = 700 mm hT1 = T + Cw m but need not be taken greater than 1.36T hT1 = 23.12 Cw = a wave head, in meters, 7.71 x 10–2Le–0,0044L Cw = 6.37 Selected t

∴t =

= 12.48 mm 20 mm (Lloyd’s Grade DH32)

195


8.4.4 Bottom shell and bilge

√h k T2

t

=

0.0052s

hT2

=

T + 0.5CW m but need not be taken greater than 1.2T

=

19.93

FB

=

0.67 (refer ‘DEFINITIONS’)

k

=


∴t

=

10.27 mm

Selected t

=

18 mm (Lloyd’s Grade DH32)

1.8-FB

8.4.5 Keel Plating

Keel plating should not be less than thickness of bottom shell + 2 mm ∴t

=

20 mm,

But need not exceed t Selected t

=

25 √ k = 22.08 mm

=

22 mm

Width of keel plate is to be not less than 70B mm, but need not exceed 1800 mm and is to be not less than 750 mm. (LRS part 4, chapter1, and table 1.5.1) 70B

=

3409 mm

Selected w

=

1800 mm

8.4.6 Inner bottom Plating

t

=

t0 / √ 2-FB

t0

=

0.005s√ kh1

s

=

spacing of inner bottom longitudinal = 700mm

k

=

0.78

h

=

distance in m, from the plate in consideration to the highest point of the tank, excluding hatchway.

R

=

0.354

b1

=

B/2 = 24.35 m

h1

=

0.72 (h+Rb1)

=

21.15

196


t0

=

14.22 mm

t

=

12.33 mm Selected = 14 mm (Lloyd’s Grade DH32)

8.5 Hull Framing [LRS Part 4, Chapter 9, Section 5] 8.5.1 Bottom Longitudinals

The section modulus of bottom longitudinals within the cargo tank region is not to be less than greater of the following: a) Z = 0.056kh1sle2F1FS cm3 K

=


h1

=

(h0 + D1/8), but in no case be taken less than L1/56 m or (0.00L1 + 0.7) m, whichever is greater & need not be taken greater than (0.75 D + D1/8), for bottom longitudinals.

=

19.82m

=

distance in m, from the midpoint of span of stiffener to highest point of tank, excluding hatchway.

=

22 m

D1

=

16 m (refer ‘DEFINITIONS’)

s

=

spacing of bottom longitudinals = 700 mm

le

=

effective span of longitudinals which are assumed to be supported by web frames spaced at 5s, where s is the basic frame spacing in midship region (850 mm ) not to be taken less than 1.5 m in double bottom and 2.5 m else where.

le

=

4.25 m

F1

=

Dc1/(25D-20h)

=

0.133

c1

=

75/(225 – 150FB), at base line of ship.

FB

=


∴c1

=

0.667

h

=

distance of longitudinal below deck at side, in meters

=

23.76 m

D

=

23.76 m (refer ‘DEFINITIONS’)

∴F1

=

0.133

FS

=

1, at upper deck at side and at the base line.

h0

197


b)

∴Z

=

1459.5 cm3

Z

=

0.0051kh3sle2F2 cm3

k

=


h3

=

75D+Rb1

b1

=

24.35 m

R

=

(0.45+0.1 L/B)(0.54 – L/1270) = 0. 354

D1

=

16 m

h3

=

26.44 m

F2

=

Dc2/ (3.18D-2.18h) = 0.785

c2

=

165/ (345-180FB)

s

=

700 mm

le

=

4.25 m

∴Z

=

1044.8 cm3

Greater of the two is to be taken, i.e. Z = 1459.5 cm3 Selected 400 x 18 HB 8.5.2 Deck Longitudinals (LRS, Part 4, Chapter 9.5.3.1)

The modulus of bottom longitudinals within the cargo tank region is not to be less than greater of the following: a)

Z

=

0.056kh1sl2eF1FS cm3

k

=


h1 h0

= =

(h0 + D1/8), but in no case be taken less than L1/56 m. 0 ( for deck longitudinals)

D1

=

16

(h0 + D1/8)

=

2

L1

=

190

L1/56

=

3.39

0.01L1 +0.7

=

2.6

∴h1

=

L1/56

s

=

700 mm

le

=

4.25m

F1

=

Dc1 / (4D + 20h)

h

=

0 (for deck longitudinals)

c1

=

60 / (225 – 165FD) at deck

FD

=


∴ c1

=

0.595

=

3.39

198


∴F1

=

0.148

Fs

=

1, at upper deck at side and at baseline of ship

∴Z

=

277.06 cm3

b) Z = 0.0051kh3sle2F2 cm3 R = bi = h3 = s = le = F2 = c2 = FD = ∴c2 = ∴F2 = ∴Z =

0.354 B/2 = 24.35 m h0 + Rb1 = 8.62 m 700 mm 4.25m Dc2 / (D + 2.18h) 165 / (345 – 180FD) 0.75 (refer ‘DEFINITIONS’) 1.0 1.0 433.5 cm3

Greatest of the two is to be taken, i.e. Z = 433.5 cm3 250 x 12 HB section is selected (LRS Part 4, Chapter 9. 5.3.1)

8.5.3 Side Shell Longitudinals

From standardization point of view the side shell is divided into longitudinal fields as shown in fig 8.3. Design of the longitudinals for each field is done using the information for the lowest longitudinal in each field. 8.5.4 Inner hull and CL bulkhead longitudinals

The modulus of side shell longitudinals within the cargo tank region is not to be less than greater of the following: a)

Z

=

0.056kh1sle2F1Fs cm3

b)

Z

=

0.0051kh3sle2F2 cm3

=

(h0 + D1/8), but in no case be taken less than L1/56 m or 0.01L1 +0.7 m whichever is the greater.

Where, h1 s

=

700 mm

le

=

4.25m

k

=

0.78

FD

=

0.75

D1

=

16

L1

=

190m

199


L1/56

=

3.39

h

=

distance of longitudinal below deck at side, in meters

h3

=

h0 + Rb1

For side longitudinals above D/2, F1

=

Dc1 / (4D + 20h)

F2

=

Dc2 / (D + 2.18h)

For side longitudinals below D/2, F1

=

Dc1/(25D-20h)

F2

=

Dc2/(3.18D-2.18h)

c1

=

60 / (225 – 165FD) at deck

=

1.0 at D/2

=

75/(225 – 150FB), at base line of ship

=

165/(345 – 180FB) at deck

=

1.0 at D/2

=

165/(345 – 180FD) at baseline of ship

c2

Fig 8.4 Side shell regions

200


Table 8.8 – Determination of scantlings of side shell longitudinals ITEM ho D1 h1= h0+D1/8 h3 F1 F2 Fs a) Z b) Z Taken Z (cm3) Section Scantling Z of taken 3

REG 1

REG 2

5.21 16 7.21 13.83 0.113 0.702 1 450.405 488.61 488.61 HB 260 x 11 488.61

20.76 16 22.76 29.38 0.0777 0.5468 1 976.925 808.12 976.92 HB 340 x 13 976.92

8.6 Inner Hull, Inner Bottom and Longitudinal Bulkheads (LRS Part 4, Chapter 9, Section 6) The inner hull, inner bottom and longitudinal bulkheads are longitudinally framed. The symbols used in this section are defined as follows: b1

=

the greatest distance in meters, from the centre of the plate panel or midpoint of the stiffener span, to the corners at top of the tank on either side.

c1

=

60 / (225 – 165FD) at deck

=

1.0 at D/2

=

75/(225 – 150FB), at base line of ship

=

165/(345 – 180FB) at deck

=

1.0 at D/2

=

165/(345 – 180FD) at baseline of ship

=

load height, in meters measured vertically as follows:

c2

h

201


(a) for bulkhead plating the distance from a point one third of the height of the plate panel above its lower edge to the highest point of the tank, excluding hatchway (b) for bulkhead stiffeners or corrugations, the distance from the midpoint of span of the stiffener or corrugation to the highest point of the tank, excluding hatchway h1 = (h + D1/8), but not less than 0.72 (h + Rb1) = (h + D1/8), in meters, but in no case be taken less than L1/56 m or h2 (0.01L1 + 0.7) m, whichever is greater = distance of longitudinal below deck at side, in meters, but is not to h3 be less than 0 h4 = h + Rb1 h5 = h2 but is not to be less than 0.55h4 t0 = 0.005s √kh1 t1 = t0(0.84 + 0.16(tm/t0)2) tm = minimum value of t0 within 0.4D each side of mid depth of bulkhead 8.6.1 Inner Hull Longitudinal Bulkhead Plating

For the determination of scantlings of longitudinal bulkhead plating and inner hull plating’s areas follows. (Refer fig 8.4)

ITEM h D1

Region 1 5.41 16

Region 2 19.09

ice belt 15.35

16

16

h1

10.101

21.09

17.35

h2

7.41

21.09

17.35

h4

14.029

27.7099

23.96

h5

7.7164

21.09

17.35

t0

9.824

14.195

12.875

10.952 12

13.7928 14

12.875 13

t1 taken

8.6.2 CL Longitudinal Bulk Head Longitudinals and Inner Hull Longitudinals

Inner hull and longitudinal bulkheads are to be longitudinally framed . The modulus of longitudinals is not to be less than greater of the following: (a) Z = 0.056kh2sl2eF1 cm3 (b) Z = 0.0051kh4sl2eF2 cm3 202


The inner hull and bulkhead plating is divided into various strakes for the determination of center line bulkhead longitudinals and inner hull longitudinals. s

=

700 mm

le

=

4.25m

Table.8.9 Determination of scantlings of CL longitudinal bulkhead longitudinal and inner hull longitudinal. ITEM b1 h1 h2 h3 h4 c1 c2 F1 F2 Z1 Z2 Taken Z (cm3) Section Scantling

Region 1

5.41 24.35 16 10.10 7.41 6.5 14.03 0.7 0.87 456.380 405.448 456.380 HB 250 X 13

Region 2 19.09

Between 1 & 2 15.35

24.35 16 21.09 21.09 17 27.71 0.7 0.87 912.923 435.494

24.35 16 17.35 17.35 13.5 23.97 1 1 751.030 692.703

912.923 HP

751.030 HP

325 X 17

325 X 12

8.6.3 Inner Bottom Plating and Longitudinals

The inner bottom is to be longitudinally framed and the inner bottom plating thickness is to be t

=

t0 / √ 2-FB

t0

=

0.005s√ kh1

s

=

spacing of inner bottom longitudinal = 700mm

k h

= =

R b1 h1

= = = = =

0.78 distance in m, from the plate in consideration to the highest point of the tank, excluding hatchway = 20.76 m 0.354 (refer previous sections) B/2 = 24.35 m 0.72 (h+Rb1) 21.15 14.21 mm

t0

203


t Selected

= =

12.32 mm 14 mm

The modulus of longitudinals is not to be less than greater of the following: (a) Z = 0.056kh2sl2eF1 cm3 h = 19.38 m = 16 m D1 h2 = h + D1 / 8 = 22.76 m = 0.078 F1 ∴Z = 985.2 cm3 (b) Z = 0.0051kh4sl2eF2 cm3 = h + Rb1 = 27.709m h4 F2 = 0.316 ∴Z

=

440.67 cm3

Selected Z = 985.2 cm3. Selected HB 330 x 13

8.7 Primary Members Supporting the Hull Longitudinal Framing 8.7.1 Centre girder

(LRS Part 4, Section 9.3.3)

(a) Minimum depth of centre girder dDB

=

28B + 205√ T mm

dDB

=

2202.6 mm

dDB

=

3000 mm

Given 3.0 m. (b)

Minimum thickness of centre girder (LRS, Part 4.9.3.4) t

=

(0.008 dDB + 1) √ k

=

22.07 mm

Given thickness =

22 mm

8.7.2 Floors and Side Girders

t

=

(0.007dDB + 1) √ k

=

19.43 mm

But not to exceed 12√ k

=

Given thickness

=

10.6 mm

=

16 mm

∴t

8.7.3 Deck Transverses

10.6 mm

(LRS Part 4.10.2.8)

Section modulus of deck transverses is not to be less than 204


Z s L ST

= = = = =

53.75 (0.0269sL + 0.8) (ST + 1.83) k cm3 4.25 m 229.8 m span of transverse 8.116 m

∴Z

=

12871.3 cm3

Taken T section 1500 X 14 +600 X 20 is selected. 8.7.4 Vertical web on centreline longitudinal bulkhead Section modulus of vertical web is to be not less than Z = K3shsSs2k (sm3) K3 = 1.88, s = 4.25 = distance between the lower span point of the vertical web hs and the moulded deckline at centreline, in meters = 20 m = span of vertical web, in meters, and is to be measured Ss between end span points. = 12.75 m

∴Z

=

18476.0 cm3

Taken T section 1250x 12+ 500x 18

8.8 Primary Members End Connections [LRS Part 3, Chapter 10, Section 3] The following relations govern the scantlings of bracket: (a + b) ≥ 2l

l

8.8.1

a

≥ 0.8 l

b

≥ 0.8 l =

90

√ (14 +Z√ Z)

2

-1

mm

Bracket connecting deck transverse and inner hull

√ (14 +Z√ Z)

l

=

90

2

Z

=

12871.3 cm3

-1

205

mm


=

90 {2 (√12871.3 / [14 + √ 12871.3]) – 1}

=

1718.8 mm

a ≥ 0.8l

=

1375 mm

b ≥ 0.8l

=

1375 mm

l

Given a

=

2300 mm and b = 2000 mm

t

=

thickness of web itself

= 25 mm

Flange breadth to be not less than bf

=

40 (1 + Z / 1000) mm, but not less than 50mm

=

40 (1 + 12871.3 / 1000)

=

554 mm

Taken 750 mm 8.8.2

Bracket connecting deck transverse and center line bulkhead web

√ (14 +Z√ Z)

l

=

90{ 2

- 1}

mm

Z

=

14602 cm3

l

=

90 {2 (√14602/ [14 + √ 14602]) – 1}

=

1783.1 mm

a ≥ 0.8l

=

1426.5 mm

b ≥ 0.8l

=

1426.5 mm

Given a

=

2400 mm and b = 2000 mm

t

=


= 25 mm


=


=

40 (1 + 14602/ 1000)

=

624.08 mm

Taken 750 mm 8.8.3 Bracket connecting centre line vertical web and inner bottom plating

√ (14 +Z√ Z)

l

=

90{ 2

Z

=

14602cm3

l

=

90 {2 (√14602/ [14 + √ 14602]) – 1}

=

1783.1 mm

=

1426.5 mm

a ≥ 0.8l

206

- 1}

mm


b ≥ 0.8l

=

1426.5 mm

Given a

=

2400 mm and b = 2000 mm

t

=


= 25 mm


=


=

40 (1 + 14602/ 1000)

=

624.08 mm

Taken 750 m Table 8.3 Section Modulus Calculation

ITEMS Deck Plate Sheerstrake Plate Above IceBelt Plate Ice Belt Plate

L (m)

t(m)

NO

AREA (m2)

2

LEVER

A*L

L*A (4m)

(4m)Iown 1.57E-05

23.5

0.02

2

0.94

23.76

22.334

530.6653

3

0.02

2

0.12

22.26

2.6712

59.46091

0.045

2.5

0.02

2

0.1

19.51

1.951

38.06401

0.026042

12.5

0.024

2

0.6

12

7.2

86.4

3.90625

3

0.02

2

0.12

4.26

0.5112

2.177712

0.045

Bottom Shell Plate

19

0.02

2

0.76

0.01

0.0076

0.000076

1.27E-05

Bottom Bilge Plate

6

0.02

2

0.24

1.25

0.3

0.375

0.36

1.8

0.022

1

0.0396

0.011

0.0004

4.79E-06

1.6E-06

4

0.014

2

0.112

4.5

0.504

2.268

0.074667

18.35

0.014

2

0.5138

3

1.5414

4.6242

4.2E-06

Centre Girder

3

0.022

1

0.066

1.5

0.099

0.1485

0.0495

Side Girder

3

0.015

6

0.27

1.5

0.405

0.6075

0.03375

CL bhd reg 1 CL bhd reg Bb/w 1 &2

5

0.012

3

0.18

21.26

3.8268

81.35777

0.125

13

0.013

1

0.169

12.26

2.0719

25.40198

2.380083

2.76

0.014

1

0.03864

4.38

0.1692

0.741285

0.024529

5

0.012

2

0.12

21.26

2.5512

54.23851

0.125

13

0.013

2

0.338

12.26

4.1439

50.80397

2.380083

Below Ice Belt Plate

Keel Plate Margin Plate Inn Bot Plate

CL bhd reg 2 IB hull plate reg 1 IB hull plate reg b/w 1&2

2.76

0.014

2

0.07728

4.38

0.3385

1.48257

0.024529

Wing Tank Girder 1

3

0.012

2

0.072

6

0.432

2.592

4.32E-07

Wing Tank Girder 2

3

0.012

2

0.072

9

0.648

5.832

4.32E-07

Wing Tank Girder 3

3

0.012

2

0.072

12

0.864

10.368

4.32E-07

Wing Tank Girder 4

3

0.012

2

0.072

15

1.08

16.2

4.32E-07

Wing Tank Girder 5

3

0.012

2

0.072

18

1.296

23.328

4.32E-07

Wing Tank Girder 6

3

4.32E-07

IB hull plate reg 2

Deck Longitudinals

0.012

2

0.072

21

1.512

31.752

250 x 12

68

0.26316

23.6

6.2106

146.5696

207


Inner Hull Longls

1

250 x 13

2

0.0084

23.06

0.1937

4.466814

2

250 x 13

2

0.0084

22.36

0.1878

4.199745

3

250 x 13

2

0.0084

21.66

0.1819

3.940907

4

250 x 13

2

0.0084

20.96

0.1761

3.690301

5

250 x 13

2

0.0084

20.26

0.1702

3.447928

6

250 x 13

2

0.0084

19.56

0.1643

3.213786

7

250 x 13

2

0.0084

18.86

0.1584

2.987877

8

325 x 12

2

0.0108

18.51

0.1999

3.700297

9

325 x 12

2

0.0108

18.16

0.1961

3.561684

10

325 x 12

2

0.0108

17.81

0.1923

3.425718

11

325 x 12

2

0.0108

17.46

0.1886

3.292397

12

325 x 12

2

0.0108

17.11

0.1848

3.161723

13

325 x 12

2

0.0108

16.76

0.181

3.033694

14

325 x 12

2

0.0108

16.41

0.1772

2.908311

15

325 x 12

2

0.0108

16.06

0.1734

2.785575

16

325 x 12

2

0.0108

15.71

0.1697

2.665484

17

325 x 12

2

0.0108

15.36

0.1659

2.54804

18

325 x 12

2

0.0108

15.01

0.1621

2.433241

19

325 x 12

2

0.0108

14.66

0.1583

2.321088

20

325 x 12

2

0.0108

14.31

0.1545

2.211582

21

325 x 12

2

0.0108

13.96

0.1508

2.104721

22

325 x 12

2

0.0108

13.61

0.147

2.000507

23

325 x 12

2

0.0108

13.26

0.1432

1.898938

24

325 x 12

2

0.0108

12.91

0.1394

1.800015

25

325 x 12

2

0.0108

12.56

0.1356

1.703739

26

325 x 12

2

0.0108

12.21

0.1319

1.610108

27

325 x 12

2

0.0108

11.86

0.1281

1.519124

28

325 x 12

2

0.0108

11.51

0.1243

1.430785

29

325 x 12

2

0.0108

11.16

0.1205

1.345092

30

325 x 12

2

0.0108

10.81

0.1167

1.262046

31

325 x 12

2

0.0108

10.46

0.113

1.181645

32

325 x 12

2

0.0108

10.11

0.1092

1.103891

33

325 x 12

2

0.0108

9.76

0.1054

1.028782

34

325 x 12

2

0.0108

9.41

0.1016

0.956319

35

325 x 12

2

0.0108

9.06

0.0978

0.886503

208


36

325 x 12

2

0.0108

8.71

0.0941

0.819332

37

325 x 12

2

0.0108

8.36

0.0903

0.754808

38

325 x 12

2

0.0108

8.01

0.0865

0.692929

39

325 x 12

2

0.0108

7.66

0.0827

0.633696

40

325 x 12

2

0.0108

7.31

0.0789

0.57711

41

325 x 12

2

0.0108

6.96

0.0752

0.523169

42

325 x 12

2

0.0108

6.61

0.0714

0.471875

43

325 x 12

2

0.0108

6.26

0.0676

0.423226

44

325 x 17

2

0.0134

5.76

0.0772

0.44458

45

325 x 17

2

0.0134

5.26

0.0705

0.370746

46

325 x 17

2

0.0134

4.76

0.0638

0.303612

47

325 x 17

2

0.0134

4.26

0.0571

0.243178

48

325 x 17

2

0.0134

3.76

0.0504

0.189444

Bottom Longitudinals

400 x 18

64

0.64

0.2

0.128

0.0256

Inner Bottom Longls

330 x 13

50

0.32

2.85

0.912

2.5992

1

250 x 13

2

0.0084

23.06

0.1937

4.466814

2

250 x 13

2

0.0084

22.36

0.1878

4.199745

3

250 x 13

2

0.0084

21.66

0.1819

3.940907

4

250 x 13

2

0.0084

20.96

0.1761

3.690301

5

250 x 13

2

0.0084

20.26

0.1702

3.447928

6

250 x 13

2

0.0084

19.56

0.1643

3.213786

7

250 x 13

2

0.0084

18.86

0.1584

2.987877

8

330 x 15

2

0.0132

18.51

0.2443

4.522585

9

330 x 15

2

0.0132

18.16

0.2397

4.35317

10

330 x 15

2

0.0132

17.81

0.2351

4.186989

11

330 x 15

2

0.0132

17.46

0.2305

4.024041

12

330 x 15

2

0.0132

17.11

0.2259

3.864328

13

330 x 15

2

0.0132

16.76

0.2212

3.707848

14

330 x 15

2

0.0132

16.41

0.2166

3.554603

15

330 x 15

2

0.0132

16.06

0.212

3.404592

16

330 x 15

2

0.0132

15.71

0.2074

3.257814

17

330 x 15

2

0.0132

15.36

0.2028

3.114271

18

330 x 15

2

0.0132

15.01

0.1981

2.973961

19

330 x 15

2

0.0132

14.66

0.1935

2.836886

Side longitudinals

209


20

330 x 15

2

0.0132

14.31

0.1889

2.703045

21

330 x 15

2

0.0132

13.96

0.1843

2.572437

22

330 x 15

2

0.0132

13.61

0.1797

2.445064

23

330 x 15

2

0.0132

13.26

0.175

2.320924

24

330 x 15

2

0.0132

12.91

0.1704

2.200019

25

330 x 15

2

0.0132

12.56

0.1658

2.082348

26

330 x 15

2

0.0132

12.21

0.1612

1.96791

27

330 x 15

2

0.0132

11.86

0.1566

1.856707

28

330 x 15

2

0.0132

11.51

0.1519

1.748737

29

330 x 15

2

0.0132

11.16

0.1473

1.644002

30

330 x 15

2

0.0132

10.81

0.1427

1.542501

31

330 x 15

2

0.0132

10.46

0.1381

1.444233

32

330 x 15

2

0.0132

10.11

0.1335

1.3492

33

330 x 15

2

0.0132

9.76

0.1288

1.2574

34

330 x 15

2

0.0132

9.41

0.1242

1.168835

35

330 x 15

2

0.0132

9.06

0.1196

1.083504

36

330 x 15

2

0.0132

8.71

0.115

1.001406

37

330 x 15

2

0.0132

8.36

0.1104

0.922543

38

330 x 15

2

0.0132

8.01

0.1057

0.846913

39

330 x 15

2

0.0132

7.66

0.1011

0.774518

40

330 x 15

2

0.0132

7.31

0.0965

0.705357

41

330 x 15

2

0.0132

6.96

0.0919

0.639429

42

330 x 15

2

0.0132

6.61

0.0873

0.576736

43

330 x 15

2

0.0132

6.26

0.0826

0.517276

44

340 x 13

2

0.012

5.56

0.0667

0.370963

45

340 x 13

2

0.012

4.86

0.0583

0.283435

46

340 x 13

2

0.012

4.16

0.0499

0.207667

47

340 x 13

2

0.012

3.46

0.0415

0.143659

48

340 x 13

2

0.012

2.76

0.0331

0.091411

49

340 x 13

2

0.012

2.06

0.0247

0.050923

50

340 x 13

2

0.012

1.36

0.0163

0.022195

51

340 x 13

2

0.012

0.66

0.0079

0.005227

1

250 x 13

1

0.0042

23.06

0.0969

2.233407

2

250 x 13

1

0.0042

22.36

0.0939

2.099872

CL Longl Bulkhead

210


3

250 x 13

1

21.66

0.091

1.970454

4

250 x 13

1

0.0042

20.96

0.088

1.845151

5

250 x 13

1

0.0042

20.26

0.0851

1.723964

6

250 x 13

1

0.0042

19.56

0.0822

1.606893

7

250 x 13

1

0.0042

18.86

0.0792

1.493938

8

325 x 12

1

0.0054

18.16

0.0981

1.780842

9

325 x 12

1

0.0054

17.46

0.0943

1.646199

10

325 x 12

1

0.0054

16.76

0.0905

1.516847

11

325 x 12

1

0.0054

16.06

0.0867

1.392787

12

325 x 12

1

0.0054

15.36

0.0829

1.27402

13

325 x 12

1

0.0054

14.66

0.0792

1.160544

14

325 x 12

1

0.0054

13.96

0.0754

1.052361

15

325 x 12

1

0.0054

13.26

0.0716

0.949469

16

325 x 12

1

0.0054

12.56

0.0678

0.851869

17

325 x 12

1

0.0054

11.86

0.064

0.759562

18

325 x 12

1

0.0054

11.16

0.0603

0.672546

19

325 x 12

1

0.0054

10.46

0.0565

0.590823

20

325 x 12

1

0.0054

9.76

0.0527

0.514391

21

325 x 12

1

0.0054

9.06

0.0489

0.443251

22

325 x 12

1

0.0054

8.36

0.0451

0.377404

23

325 x 12

1

0.0054

7.66

0.0414

0.316848

24

325 x 12

1

0.0054

6.96

0.0376

0.261585

25

325 x 12

1

0.0054

6.26

0.0338

0.211613

26

325 x 17

1

0.0067

5.56

0.0373

0.207121

27

325 x 17

1

0.0067

4.86

0.0326

0.158251

28

325 x 17

1

0.0067

4.16

0.0279

0.115948

29

325 x 17

1

0.0067

3.46

0.0232

0.08021

7.75748

10.2374

79.416

1405.963

30

Total

0.0042

9.599469

Height of NA =10.237 I ref I na Z deck Z keel Z Req

=1415.56 =602.54 =44.44 =58.85

43.31

m3

Here ZDECK and ZKEEL are getting more than the minimum section modulus required. So the design is satisfactory

211


212

Midship

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