Section 1 General

1.1.1 This Chapter applies to all types of ship covered by Pt 4 Ship Structures (Ship Types) except where specifically stated otherwise.

1.1.2 The requirements given are those specific to fore ends and relate to structure situated in the region forward of 0,3L from the forward perpendicular.

1.1.3 Requirements for cargo space structure within this region not dealt with in this Chapter are to be as detailed in the relevant Chapter of Pt 4 Ship Structures (Ship Types) for the particular ship type.

1.1.4 The requirements in this Chapter are not applicable to Double Hull Oil Tankers or Bulk Carriers with a CSR notation. See Pt 1, Ch 2, 2.3 Class notations (hull).

1.2.1 The Rules provide for both longitudinal and transverse framing systems.

1.2.2 In the case of container ships and open type ships, additional requirements may apply as detailed in Pt 4, Ch 8 Container Ships.

1.2.3 In the case of fast cargo ships, the additional requirements given in Pt 4, Ch 1, 3 Longitudinal strength are to be complied with where applicable.

1.2.4 The requirements regarding minimum bow height given in Pt 3, Ch 3, 6 Minimum bow heights, reserve buoyancy and extent of forecastle are to be complied with where applicable.

1.3.1 Suitable scarfing arrangements are to be made to ensure continuity of strength and the avoidance of abrupt structural changes.

1.3.2 Where longitudinal framing terminates and is replaced by a transverse system, adequate arrangements are to be made to avoid an abrupt changeover. Where a forecastle is fitted extending aft of 0,15L from the F.P., longitudinal framing at the upper deck and topsides is generally to be continued forward of the end bulkhead of this superstructure. In bulk carriers and oil tankers (see Pt 3, Ch 5, 1.1 Application 1.1.4) the longitudinal framing at the upper deck is to be maintained over the cargo space region and continued over the fore peak region.

1.3.3 In container or similar ships having continuous side tanks or double skin construction in way of the cargo spaces, the longitudinal bulkheads are to be continued as far forward as is practicable and are to be suitably tapered at their ends. Where, due to the ship's form, such bulkheads are stepped, suitable scarfing is to be arranged.

1.3.4 In bulk carriers (see Pt 3, Ch 5, 1.1 Application 1.1.4) the topside tank and double bottom hopper tank structures are to be maintained over the cargo space region, and suitable taper brackets are to be arranged in line with the end of these tank structures in the fore peak region. In addition, in way of the cargo space forward bulkhead, a girder or intercostal bulb plate stiffeners (fitted between and connected to the bulkhead vertical stiffeners), are to be arranged on the forward side in line with the sloped bulkheads of the topside and hopper tanks clear of the taper brackets.

1.4.1 The following symbols and definitions are applicable to this Chapter unless otherwise stated:

=

overall length of stiffening member, in metres, see Pt 3, Ch 3, 3.3 Determination of span point

e

=

effective length of stiffening member, in metres, see Pt 3, Ch 3, 3.3 Determination of span point

=

inertia of stiffening member, in cm4, see Pt 3, Ch 3, 3.2 Geometric properties of section

1.4.2 For the purpose of this Chapter the forward perpendicular, F.P., is defined as the forward limit of the Rule length L.

1.5.1 The bottom forward of a sea-going ship is to be additionally strengthened, except where the ship is so designed that a minimum draught forward, T _FB, of 0,045L can be achieved for any ballast or part loaded condition. This draught is to be indicated on the shell expansion plan, the plan showing the internal strengthening, the Loading Manual and loading instrument, where fitted, see Pt 3, Ch 4, 8 Loading guidance information.

1.5.2 The requirements for the additional strengthening apply to ships where L is greater than 65 m. Where a ship is classed for service in protected waters or extended protected waters, compliance with the requirements of this Section may be modified or waived altogether.

1.5.3 The additional strengthening is to extend forward of 0,3L from the F.P. over the flat of bottom and adjacent plating with attached stiffeners up to a height of 0,002L above the base line or 300 mm whichever is the lesser.

1.5.4 The scantling requirements outside the areas defined in Pt 3, Ch 5, 1.5 Strengthening of bottom forward 1.5.3 are to be suitably tapered to maintain adequate continuity of strength in both longitudinal and transverse directions.

1.5.5 The requirements for the additional strengthening within the region defined in Pt 3, Ch 5, 1.5 Strengthening of bottom forward 1.5.3 are given in Table 5.1.1 Additional strengthening of bottom forward , or may be obtained by direct calculation. Where T _FB is less than 0,01L, the additional strengthening is to be specially considered.

1.5.6 Bottom longitudinals are to pass through and be supported by the webs of primary members. The vertical web stiffeners are to be connected to the bottom longitudinals. The cross-sectional area of the connections is to comply with the requirements given in Table 5.1.1 Additional strengthening of bottom forward .

1.5.7 The scantlings required by this Section must in no case be less than those required by the remaining Sections in Pt 3, Ch 5 Fore End Structure.

1.5.8 For minimum draught forward, T _FB between 0,01L and 0,045L, the equivalent slamming pressure expressed as a head of water, h _s, is to be obtained from Figure 5.1.1 Pressure heads, where h _max is calculated from the following expressions:

	65 < L ≤ 169 m, h max	=	F m
	169 < L ≤ 180 m, h max	=	130F m
	L > 180 m, h max	=	130 Fe–0,0125(L-180)0,705 m

where

F	=
	=	and
e	=	base of natural logarithms, 2,7183

1. The application of the maximum pressure for forward of 0,3L from the F.P. is as indicated in Figure 5.1.1 Pressure heads. For C _b between 0,70 and 0,80 its position may be obtained by linear interpolation.

2. Where the bottom plating forms the boundary of a double bottom tank, deep tank or double skin tank which is full in all ballast conditions, then for such conditions the head, h _s, may be reduced by 1,25 times the head, in metres, of ballast water to top of tank.

3. For bulk carriers (see Pt 3, Ch 5, 1.1 Application 1.1.4) the reduction to the head, h _s, is not to exceed the head, in metres, of ballast water to the top of the hopper tank or 1,25 times the depth, in metres, of the double bottom tank, whichever is the greater.

4. For ballast and part loaded conditions where the draught forward is less than 0,045L and the reduction to the head, h _s, has been applied, the ballast tanks are to be filled and a note added to the loading booklet to this effect, see Pt 3, Ch 4, 8.2 Loading Manual 8.2.4.(d).

Figure 5.1.1 Pressure heads

1.6.1 The requirements of this Section apply to all ships except those defined in Pt 4, Ch 2 Ferries, Roll On-Roll Off Ships and Passenger Ships and Pt 4, Ch 8 Container Ships.

1.6.2 The side structure in the area forward of 0,075L from the F.P. and above the summer load waterline is to be strengthened against bow flare impact pressure. The strengthening is to extend vertically to the uppermost deck level, including the forecastle deck, if fitted, but need not exceed the level of T + 1,65H _b above the base line, where H _b is the minimum bow height, in metres, as derived in Pt 3, Ch 1, 6.1 Principal particulars 6.1.11.

1.6.3 The flare angle, α, is the angle between the vertical axis and the tangent of the outer shell measured normal to the shell in a vertical plane, at the point under consideration. The entry angle, β, is the angle between the longitudinal axis and the waterplane tangent measured on the outer shell, at the point under consideration. The flare angle may normally be derived in accordance with Figure 5.1.2 Flare angle determination.

Table 5.1.1 Additional strengthening of bottom forward

Item		Requirements
(1)	Longitudinally framed bottom shell plating (including keel), see Notes 1 and 2
(2)	Bottom longitudinals - other than flat bars
(3)	Bottom longitudinals - flat bars	Will be specially considered
		Transverse framing	Longitudinal framing
(4)	Primary structure in way of single bottoms	(a) Centre girder:	(a) Ships having one or more longitudinal bulkheads:
		Scantlings as required by item (1) in Table 5.5.1 Single bottom construction forward, except that in determining Z in way of a deep tank forward of 0,2L from the F.P. the value of h5 is to be increased by the following percentages:	(i) Centre girder
		where TFB ≤ 0,03L 2, 30 per cent	Scantlings as required by item (4) in Table 5.5.1 Single bottom construction forward and (iii)
		where TFB ≥ 0,04L 2, 0 per cent	(ii) Bottom transverses
		The increase in h5 for intermediate values of TFB to be obtained by interpolation	Maximum spacing
		(b) Floors:	As for midships region
		Scantlings as required by item (2) in Table 5.5.1 Single bottom construction forward, except that in way of dry cargo spaces the minimum face area is to be increased by the following percentages:	Scantlings as required by Pt 4, Ch 9, 9 Primary members supporting longitudinal framing or Pt 4, Ch 10, 2 Primary members supporting longitudinal framing
		where TFB ≤ 0,03L 2, 50 per cent	(iii) For horizontally stiffened longitudinal bulkheads and girders the depth to thickness ratio of the panel attached to the bottom shell plate is not to exceed
		where TFB ≥ 0,04L 2, 0 per cent	(iv) Where TFB, < 0,025L 2the scantlings and arrangements will receive individual consideration
		The increase of minimum face area for intermediate values of TFB is to be obtained by interpolation	(b) Other ship arrangements will receive individual consideration
		(c) Side girders:
		Arrangement and scantlings as required by Pt 3, Ch 5, 5.2 Single bottoms − Transverse framing 5.2.2 and Pt 3, Ch 5, 5.2 Single bottoms − Transverse framing 5.2.3, with the addition of intermediate half-height girders or equivalent fore and aft stiffening
(5)	Primary structure in way of double bottoms, see Note 3	(a) Plate floors:	(a) Plate floors:
		Maximum spacing, every frame	Maximum spacing:
		Scantlings as required by Pt 4, Ch 1, 8 Double bottom structure	0,002s F m for TFB < 0,04L 2
		(b) Centre and side girders:	0,003s F m for TFB ≥ 0,04L 2
		Maximum spacing, 0,003S F m	but not to exceed that required by item (2) in Table 5.5.2 Double bottom construction forward
		(c) Intermediate half-height girders to be arranged midway between side girders:	Scantlings as required by Pt 4, Ch 1, 8 Double bottom structure
		Scantlings as required for non watertight side girders by Pt 4, Ch 1, 8 Double bottom structure	(b) Centre and side girders:
			Maximum spacing:
			0,003s L m for TFB < 0,04L 2
			0,004s L m for TFB > 0,04L 2
			but not to exceed that required by item (4) in Table 5.5.2
			Scantlings as required by Pt 4, Ch 1, 8 Double bottom structure
(6)	Primary structure in way of double bottoms supported by longitudinal bulkheads	–	The scantlings and arrangements will receive individual consideration on the basis of direct calculations using, if necessary, a suitably defined two-dimensional grillage model, see Pt 3, Ch 1, 3 Equivalents
Symbols
L, T, s, k as defined in Pt 3, Ch 5, 1.4 Symbols and definitions 1.4.1 c = 1,0 for S ≤ 2,5 m = (0,87 + 0,16S) c 1 for S > 2,5 m
c1 = 1,0 for S ≤ 1,0 m = (1,14 - 0,14S) for 1,0 m < S ≤ 4,0 m = for S > 4,0 m
dw = web depth, in mm, which for bulb flats may be taken as 0,9 times the section height
f = = but not greater than 1,0
hs = equivalent slamming pressure, in metres obtained from Pt 3, Ch 5, 1.5 Strengthening of bottom forward 1.5.8
s = e, in metres, as defined in Pt 3, Ch 5, 1.4 Symbols and definitions 1.4.1 where in way of a double bottom = S, in metres, where in way of a single bottom
S = spacing of primary members, in metres
p =
sF = spacing of transverse frames, in mm, for longitudinally framed side and bottom construction s F may be taken as sL
sL = spacing of bottom longitudinals, in mm
tw = web thickness, in mm
Af = cross-sectional area of primary member web stiffener, in cm2
Afc = effective area of primary member web stiffener in way of butted end connection to the longitudinal, in cm2
AL = area of weld of lapped connection, in cm2, calculated as total length of weld, in cm × throat thickness, in cm
Aw = area of weld of lug and web connection to the longitudinal, in cm2, calculated as total length of weld in cm × throat thickness, in cm
A1 = effective total cross-sectional area of the lug and web connection to the longitudinal, in cm2
L2 = L but need not be taken greater than 215 m
TFB = draught, in metres, at the F.P., as defined in Pt 3, Ch 5, 1.5 Strengthening of bottom forward 1.5.1
α = Af for the web stiffeners = Afc for a butted connection to the longitudinals = AL for a lapped connection
= permissible direct stress, in N/mm2, given in Table 5.1.2 Permissible stresses
= permissible shear stress, in N/mm2, given in Table 5.1.2 Permissible stresses
Note 1. If intermediate stiffening is fitted the thickness of the bottom shell plating may be 80 per cent of that required by (1) but is to be not less than the normal taper thickness.
Note 2. For transverse framing the bottom shell plating is to be specially considered.
Note 3. Particular care is to be taken to limit the size and number of openings in way of the ends of floors or girders or to fit suitable reinforcement where such openings are essential.
Note 4. The welding requirements of Pt 3, Ch 10 Welding and Structural Details, and in cargo oil tanks of tankers, the requirements of Pt 4, Ch 9, 10.14 Arrangements at intersections of continuous secondary and primary members or Pt 4, Ch 10, 7.14 Arrangements at intersections of continuous secondary and primary members, are also to be complied with.

1.6.4 The equivalent bow flare slamming head, h _S, is to be taken as:

where

V	=	as defined in Pt 3, Ch 5, 1.4 Symbols and definitions 1.4.1
α	=	flare angle, in degrees, at the point under consideration
β	=	entry angle, in degrees, at the point under consideration
δ	=	and is not to be taken less than zero
e	=	base of natural logarithms 2,7183
d	=	vertical distance, in metres, between the waterline at draught T and the point under consideration.

1.6.5 The thickness of the side shell is to be not less than:

where

sC	=	spacing of secondary stiffeners, in mm, measured along a chord between parallel adjacent members or equivalent supports, as shown in Figure 5.1.3 Chord spacing and mean chord spacing for secondary members
hS	=	bow flare slamming head, in metres, as defined in Pt 3, Ch 5, 1.6 Strengthening against bow flare slamming 1.6.4
CR	=	panel ratio factor
	=	but is not to be taken less than 0,06 or greater than 0,1
	=	overall panel length, in metres, measured along a chord between the primary members.

1.6.6 The scantlings of secondary stiffeners are not to be less than:

1. Section modulus of secondary stiffeners

   

2. Web area of secondary stiffeners

   

Table 5.1.2 Permissible stresses

Item		Direct stress,	Shear stress,
		in N/mm2 see Note	in N/mm2
Primary member web stiffener on area A f	(a) Flat bars see Note		—
	(b) Bulb plates see Note		—
	(c) Inverted angles		—
Primary member web stiffener on area Afc			—
Primary member web stiffener lapped to secondary member on area AL		—
Lug or web connection on area A1	Single	—
	Double	—
Symbols
Af, AL, A1 as defined in Table 5.1.1 Additional strengthening of bottom forward d = stiffener depth, in mm k = as defined in Pt 3, Ch 5, 1.4 Symbols and definitions 1.4.1 t = stiffener web thickness, in mm
Note to be taken not greater than

1.6.7 The scantlings of primary members are not to be less than:

1. Section modulus of primary members

   

2. Web area of primary members

   

1.6.8 For primary members with cut-outs for the passage of secondary stiffeners, and which may have web stiffeners connected to the secondary stiffener, buckling checks are to be carried out to ensure that the primary member web plating and web stiffener will not buckle under the design load. The buckling procedure to be followed is given in Table 5.1.3 Buckling procedure for primary member web plating and web stiffener. Where the web stiffener is fitted with a bracket, the buckling capability of the web stiffener in way of the cut-out is to take account of the bracket. Where no web stiffener is fitted, the buckling capability of the primary member web plating is to be checked for the total load transmitted to the connection.

1.6.9 The structural scantlings required in areas strengthened against bow flare slamming are to be tapered from 0,075L aft of fore perpendicular to meet the normal requirements at 0,15L aft of the fore perpendicular.

1.6.10 Where the stiffener web is not perpendicular to the plating, tripping brackets may need to be fitted in order to obtain adequate lateral stability.

1.6.11 For stiffeners and primary structure, where the angle between the stiffener web and the plating is less than 70°, the effective section modulus and shear area are to take account of the non-perpendicularity.

1.6.12 The side structure scantlings required by this Section must in no case be taken less than those required by the remaining Sections of Pt 3, Ch 5 Fore End Structure.

Figure 5.1.2 Flare angle determination

Figure 5.1.3 Chord spacing and mean chord spacing for secondary members

Figure 5.1.4 Mean chord spacing for primary members

Figure 5.1.5 Dimensions of critical areas of (a) primary member web plating and (b) primary web stiffener

Table 5.1.3 Buckling procedure for primary member web plating and web stiffener

Steps	Members
	Primary member web plating	Primary member web stiffener
Determination of the design compressive stress, σA, N/mm2 (kgf/mm2 )
Determination of the elastic critical buckling stress, σE, in compression, N/mm2 (kgf/mm2 )
Determination of the corrected critical buckling stress, σCR, in compression, N/mm2 (kgf/mm2 )	where where
Requirement	σCR ≥ σA
Symbols
bW, bS , W, and S are dimensions, in mm, as shown in Figure 5.1.5 Dimensions of critical areas of (a) primary member web plating and (b) primary web stiffener
hS = equivalent bow flare slamming head, in metres, as defined in Pt 3, Ch 5, 1.6 Strengthening against bow flare slamming 1.6.4
sCM = mean spacing of secondary stiffeners, in mm, as defined in Pt 3, Ch 5, 1.6 Strengthening against bow flare slamming 1.6.5
tW = thickness of primary member web plating, in mm
tS = thickness of primary member web stiffener, in mm
AW = b W t W mm2
AS = b S t S mm2
E = modulus of elasticity, in N/mm2 = 206000 N/mm2 for steel
IW =
IS =
P = total load transmitted to the connection = 10,06 SCM sCM hS x 10 –3 kN
PW = load transmitted through the primary member web plating, in kN = P – P S, or by direct calculations
PS = load transmitted through the primary member web stiffener, in kN (tonne-f), to be determined from Pt 3, Ch 10, 5.2 Arrangements at intersections of continuous secondary and primary members 5.2.7.(b), or by direct calculations
SCM = mean spacing of primary members, in metres, as defined in Pt 3, Ch 5, 1.6 Strengthening against bow flare slamming 1.6.6 σo specified minimum yield stress, in N/mm2