**3.1 General **

3.1.1 The thickness ‘t’ of plating subjected to lateral pressure given by:

where,

‘s’ is the frame spacing [mm]

p = lateral pressure [kN/m^{2}]

σa = permissible stress [N/mm^{2}] given in Table 3.1.1
p [mm]

s f . f 0.0158 t

a r a

= σ

fa = correction factor for aspect ratio of plate field

= ( 1.10 – 0.5 (s/1000 l)^{2 })^{1/2}; not to be taken more than 1.0.

fr = correction factor for curvature perpendicular to the stiffeners = (1 – 0.5 s/r)

r = radius of curvature of plating [mm]

k = material factor given in Chapter 2, Cl. 2.2 and 3.2 for steel and aluminium respectively.

**Table 3.1.1 : Allowable local bending stress **σ**a**** [N/mm**^{2}**] **

**Item ** **Framing **

**system **
**Trans.:T **

**Long.:L **

**For plating ** **For **
**secondary **

**stiffeners **

**For primary **
**girders and **
**web frames **

Bottom shell

Slamming/

Impact

Both 235/k 235/k 215/k

Sea load

T 100/k* 160/k 160/k Trans.

girder

L 120/k * 140/k* 120/k* Longl.

girder

Side shell

& longl.

Bhds.

Bow impact load

Both 235/k 235/k 215/k

Sea load

T 55/k* at deck

120/k* below D/3 from deck

160/k 160/k Trans.

Girder

L 85/k* at deck

120/k* below D/3 from deck

80/k* at deck 150/k* below D/3 from deck

120/k* Long.

Girder

Main/strength deck

T 55/k* 160/k 160/k Trans.

Girder

L 85/k* 80/k* 65/k* Long.

Girder Superstructure / deck

houses : decks/house tops.

Short decks

- 160/k 160/k 160/k

Transverse tank bulkheads and collision bulkhead

- 160/k 160/k 160/k

Transverse watertight / bulkheads

- 220/k 220/k 220/k

Superstructure and bulkheads

Deckhouse side / end bulkheads

- 235/k 220/k 220/k

* Stress values, at 0.4L amidships. To be increased to 160/k at ends and at intermediate locations values to be linearly interpolated

**3.2 Bottom and bilge plating **

3.2.1 The thickness of bottom plating corresponding to lateral pressure or impact loads is given by 3.1.1.

where,

p = lateral pressure in Chapter 3, Section 3.5 or impact pressure due to slamming given in Chapter 3, Section 3.2

3.2.2 The thickness is also be not less than:

t = (5 + 0.04L) s/sr [mm] for steel, and t = (6.5 + 0.05L) s/sr [mm] for aluminium where,

‘s’ is not to be taken less than 400 [mm]

3.2.3 The thickness of bilge plating is not to be less than the adjacent bottom or side plates whichever is greater.

3.2.4 The thickness of plates in way of shaft brackets is to be increased by 50%.

3.2.5 Sea chests are to have scantlings as required for watertight tank bulkheads with design pressure equal to sea pressure in Chapter 4, Section 3.5 plus half the slam impact pressure given in Chapter 4, Section 3.2.

**3.3 Side plating **

3.3.1 The thickness of side plating corresponding to lateral pressures or impact is given by 3.1.1.

where,

p = sea pressure as in Chapter 3, Section 3.5 or forebody side and bow impact pressure as per Chapter 3, Section 3.3.

3.3.2 The thickness should also be not less than:

t = (5 + 0.025L) s/sr for steel t = (6.0 + 0.03L) s/sr for aluminium where,

‘s’ is not to be taken less than 400 [mm]

3.3.3 The thickness of sheer strake should be not less than the adjacent side or stringer plate.

3.3.4 The thickness of sheer strake is to be increased by 30% on each side of a superstructure end bulkhead located within 0.5L amidships if the superstructure deck is a partial strength deck. The side plating of the superstructure should be given a smooth transition to the sheer strake below and its thickness is to be increased by 25% at the transition.

3.3.5 For vessels with L > 50 m where the sheer strake extends above the deck stringer plate, the top edge of the sheer strake is to be kept free from notches and isolated weld fittings and is to be ground smooth with round edges. Drainage openings with smooth transition in the longitudinal direction may be allowed.

**3.4 Deck plating **

3.4.1 The thickness of deck plating to be designed to withstand lateral pressure as given by 3.1.1.

where,

p = weather load given in Chapter 3, Section 3.5.1 or other loads as applicable 3.4.2 The thickness of deck plating is also be not less than the following:

a) For strength deck

t = (5 + 0.02L) s/sr [mm] for steel, and t = (6 + 0.03L) s/sr [mm] for aluminium.

where,

‘s’ is not to be taken less than 400 [mm]

b) For other decks

t = (4.5 + 0.01L) s/s_{r} [mm] for steel
t = (6 + 0.01L) s/sr for aluminium.

where,

‘s’ is not to be taken less than 400 [mm]

3.4.3 Adequate transverse buckling strength is to be provided for deck plating by increased thickness or by providing intercoastal transverse stiffeners.

3.4.4 Where corners of openings in the strength deck are not of streamlined shape, inserts plates are to be fitted at the corners. The insert plates are to be 25 percent thicker than the deck plating outside the line of openings and are to extend as shown in Fig.3.4.4.

**x**_{1} **x**_{2 }

**y****1****y****2** **r**

**x1,x2 > 1.5r**
**y1 > 2r**
**y2 > r**
**'r' as per **
**2.3.4**

**Fig.3.4.4 : Extent of insert plate **

**3.5 Bulkhead plating **

3.5.1 The thickness requirement corresponding to lateral pressure is given by 3.1.1.

where,

p = pressure as per Chapter 3, Section 3.6

3.5.2 The plate thickness is also not be less than the following:

a) Tank bulkheads

t = (5 + 0.02L) s/sr for steel t = (6 + 0.03L) s/sr for aluminium.

where,

‘s’ is not to be taken less than 400 [mm]

b) Ordinary watertight bulkheads t = (4 + 0.02L) s/sr for steel t = (5 + 0.025L) s/sr for aluminium.

where,

‘s’ is not to be taken less than 400 [mm]

3.5.3 The thickness of upper and lower strakes of longitudinal bulkheads are also to satisfy the buckling strength requirements given in 1.1.3.

**3.6 Superstructure and deckhouse bulkheads, bulwarks **

3.6.1 The thickness requirement for plating of superstructure end bulkheads, deckhouse sides and ends corresponding to lateral pressure is given in 3.1.1.

where,

p is the lateral pressure given in Chapter 3, Section 3.5.

3.6.2 The thickness is also be not less than the following:

a) For lowest tiers

t = (5 + 0.01L) s/sr [mm] for Steel
t = (6.5 + 0.01L) s/s_{r} [mm] for Aluminium
where,

‘s’ is not to be taken less than 400 [mm]

b) For other tiers

t = (4 + 0.01L) s/sr [mm] for Steel t = (5.5 + 0.01L) s/sr [mm] for Aluminium

where,

‘s’ is not to be taken less than 400 [mm]

3.6.3 The thickness of the bulwark plating is not to be less than that required for the superstructure side plating in the same location if the height of the bulwark is equal to or greater than 1.8 [m].

Where the height of the bulwark is 1.0 [m], the thickness is not to be less than 6.0 s/sr [mm] with a minimum of 3.0 [mm].

**3.7 Hatch covers **

3.7.1 Hatch cover plating should have same strength as the adjacent deck plating.