Section 3 Hull envelope framing

3.1.1 This Section covers the arrangements and requirements for the hull envelope plating for flush and trunk deck tankers viz: keel, bottom, bilge, side shell plating, sheerstrake, deck, trunk side and trunk deck plating so far as applicable. Tankers of Type C are to be of the flush deck type, see also Pt 4, Ch 4, 3.6 Special requirements for Type C tankers.

3.1.2 The thickness of the hull envelope plating amidships is to be not less than required in this Section, but in ships over 65 m in length, the thickness of bottom plating and top side plating (and/or longitudinal stiffening members) may require to be increased to obtain the midship section modulus as required in Pt 3, Ch 4 Longitudinal Strength.

3.1.3 The midship thicknesses are to be maintained over 0,5L amidships, except where stated otherwise in this Section and may be tapered to the end thicknesses in the fore and aft ends of the ship, see Pt 3, Ch 5 Fore End and Aft End Structure, according to the requirements for taper given inPt 3, Ch 3, 2.5 Principles for taper.

3.1.4 Openings in the shell plating are to have well rounded corners; compensation is, generally, only required for openings having a width greater than 250 mm. Openings in way of, or near to the bilge radius are to be circular or elliptical.

3.1.5 Where openings are made in the deck plating for access to tanks, the deck plating in way is, generally, to be increased in thickness to compensate for the material cut out. Where a deck longitudinal is cut in way of an opening, compensation is to be arranged to ensure full continuity of sectional area. However, no compensation need be fitted if the loss of sectional area has already been taken into consideration in calculating the actual midship hull section modulus.

3.1.6 Circular openings in the deck of a diameter of 150 mm or less need not be compensated, provided they are situated well clear of other openings and the area cut out transversely over the deck does not exceed three per cent of the total area.

3.1.7 Plate panels, in which openings are cut are, where necessary, to be adequately stiffened against compression.

3.2.1 The breadth and thickness of the keel is to comply with the requirements of Table 6.3.1 Hull envelope plating and inner bottom plating - All tankers and is to be maintained over the full length of the ship.

Table 6.3.1 Hull envelope plating and inner bottom plating - All tankers

Item and Parameter		Required minimum scantlings, see Note 1
(1)	Plate keel	0,1B m, but not less than 0,75 m
	Breadth	As bottom plating, tb
	Thickness	When there is a rise of floor, the thickness is to be increased by 1 mm
(2)	Bottom plating	Longitudinal framing	Transverse framing
	Thickness	The greater of:	The greater of:
	See note 2
(3)	Bilge Plating	Longitudinal and transverse framing
	Thickness	tb = tb + 2 mm
(4)	Bilge chine bars
	(a)	Round bars
		Diameter	3tb mm, but not less than 30 mm
	(b)	Square bars
		Width	3tb mm, but not less than 30 mm
	(c)	Angle bars
		Flange thickness	tb = 2tb mm
(5)	Side shell plating	The greater of:
	Thickness
	See Note 2
(6)	Sheerstrake
	Width	0,08D mm but not less than 0,2 m
	Thickness	t = ts + 5 mm, see Note 3
(7)	Doublers clear of sheerstrake (when fitted)
	Width	Wd= between 0,10 and 0,45 m
	Thickness	The greater of:
		t = 30Wd
		t = ts
(8)	Inner bottom plating	The greater of:
		t = 12s mm
Symbols
L, B, D, T, S, s, k and t are as defined in Pt 4, Ch 6, 1.12 Symbols and definitions 1.12.1 hg = as defined in Table 6.4.1 Hull framing - Transversely framed ships Kc = plate thickness factor = 1,5 for mild steel For stainless steel, see Pt 3, Ch 4, 7.3 Corrosion additions 7.3.7 tb = thickness of bottom plating, in mm ts = required minimum thickness for the sideshell plating calculated at the same location, in mm D1 = depth D for flush deck tankers and depth to trunk deck for trunk deck tankers
Note 1. The minimum compartment thickness of the tank structure is not to be less than as required by Pt 4, Ch 6, 1.10 Compartment minimum thickness. Note 2. For single skin tankers intended for the carriage of cargoes having relative densities (specific gravities) in excess of 1,0 and for single skin tankers with design vapour pressures in excess of 10 kPa, the thickness is also to comply with the requirements for tank boundary plating, in accordance with Section 7, whereby a minimum draught of 0,4T may be assumed to represent the counter-effect of outside water pressure. Note 3. For ships up to a length, L, of 65 m, where a substantial welded steel rubbing bar is fitted, the sheerstrake may be of the same thickness as the side shell in way.

3.3.1 The thickness of the bottom plating and side shell plating is to comply with the requirements of Table 6.3.1 Hull envelope plating and inner bottom plating - All tankers.

3.3.2 Where a reduced width of the double skin is proposed on Type C tankers, the thickness of the sideshell plating is to be increased, see Pt 4, Ch 6, 3.11 Double skin arrangement 3.11.2.

3.4.1 The thickness of the bilge plating amidships is to comply with the requirements of Table 6.3.1 Hull envelope plating and inner bottom plating - All tankers, and is to be maintained from well beyond the forward shoulder to well beyond the aft shoulder of the bilge, but at least over the midship region. For definition of shoulders, see Pt 3, Ch 5, 2.4 Shell plating.

3.4.2 The bilge radius is to be at least 10 times the thickness of the bilge plating and is to extend at least 100 mm on either side of the radius of the bilge plate.

3.4.3 Square bilges, constructed by solid round, square, or externally fitted angle bars, see Figure 6.3.1 Square bilge arrangements, are to comply with Table 6.3.1 Hull envelope plating and inner bottom plating - All tankers. The bottom plating and the side shell plating, adjacent to the round, square or angle bars, need not be increased in thickness above that of the bottom plating or side shell plating in way.

Figure 6.3.1 Square bilge arrangements

3.5.1 The width and the thickness of the sheerstrake is to comply with the requirements of Table 6.3.1 Hull envelope plating and inner bottom plating - All tankers.

3.5.2 In case of a rounded gunwale or when the sheerstrake is of the ‘tumble home’ type, a strake of increased thickness is to be fitted as high as possible, covering the area where the ship has its maximum width. The thickness and extent are to comply with Pt 4, Ch 6, 3.5 Sheerstrake 3.5.1.

3.5.3 In case of a rounded gunwale the radius of the curvature of the strake is not to be less than 10 times the actual plating thickness.

3.5.4 Where a reduced width of the double skin is proposed on Type C tankers, the thickness of the sheerstrake plating is to be increased, see Pt 4, Ch 6, 3.11 Double skin arrangement 3.11.2.

3.6.1 The thickness of the deck plating is to comply with the requirements of Table 6.3.2 Hull envelope plating - Flush deck tankers deck plating.

Table 6.3.2 Hull envelope plating - Flush deck tankers deck plating

Item and parameter	Longitudinal framing	Transverse framing
Deck plating:	The greater of:	The greater of:
Thickness
See Note	t = 10s mm	t = 10s mm
Symbols
L, B, D, S, s, k and t are as defined in Pt 4, Ch 6, 1.12 Symbols and definitions 1.12.1
NOTE
The minimum compartment thickness of the tank structure is not to be less than as required by Pt 4, Ch 6, 1.10 Compartment minimum thickness.

3.6.2 Where a reduced width of the double skin is proposed on Type C tankers, the thickness of the deck plating is to be increased, see Pt 4, Ch 6, 3.11 Double skin arrangement 3.11.2.

3.7.1 The thickness of plating of the trunk deck, trunk side and deck abreast of the trunk is to comply with the requirements of Table 6.3.3 Hull envelope plating - Trunk deck tankers trunk plating and deck plating.

Table 6.3.3 Hull envelope plating - Trunk deck tankers trunk plating and deck plating

	Item and parameter	Longitudinal framing	Transverse framing
(1)	Trunk deck plating	The greater of:	The greater of:
	Thickness
	See Note	t trd = 10st mm	t trd = 10st mm
(2)	Trunk side plating	The greater of:	The greater of:
	Thickness,	t = ttrd mm	t = ttrd mm
	see Note
(3)	Deck plating abreast trunk	The greater of:	The greater of:
	Thickness,		t = t trd mm
	see Note
		t = 10sd mm	t = 10s mm
Symbols
L, s and t as defined in Pt 4, Ch 6, 1.12 Symbols and definitions 1.12.1 s = spacing of transverse deck beams, in metres s d = spacing of longitudinals of deck abreast trunk or breadth of deck if no longitudinals are fitted, in metres, see Figure 6.3.2 Cross-section of longitudinally framed trunk deck tanker s t = spacing of trunk deck longitudinals, in metres s ts = spacing of trunk side longitudinals or height of trunk if no longitudinals are fitted, in metres, see Figure 6.3.2 Cross-section of longitudinally framed trunk deck tanker, s ts is to be taken as not less than s t t trd = thickness of trunk deck plating, in mm B trd = breadth of trunk deck, in metres D trd = depth of ship to trunk deck, measured at the middle of the length L from top of keel to top of the deck beam of the trunk deck at side of trunk, in metres
NOTE
The minimum thickness of the tank structure is not to be less than as required by Pt 4, Ch 6, 1.10 Compartment minimum thickness

Figure 6.3.2 Cross-section of longitudinally framed trunk deck tanker

3.8.1 The thickness of the deck plating is to comply with the requirements of Table 6.3.2 Hull envelope plating - Flush deck tankers deck plating.

3.8.2 Where a reduced width of the double skin is proposed on Type C tankers, the thickness of the deck plating is to be increased, see Pt 4, Ch 6, 3.11 Double skin arrangement 3.11.2.

3.9.1 The thickness of plating of the trunk deck, trunk side and the deck abreast of the trunk is to comply with the requirements of Table 6.3.3 Hull envelope plating - Trunk deck tankers trunk plating and deck plating.

3.10.1 The thickness of the inner bottom plating is to comply with the requirements of Table 6.3.1 Hull envelope plating and inner bottom plating - All tankers.

3.11.1 Where a double skin is fitted and the inner skin forms the boundary of cargo tanks, the plating of the inner skin is to comply with the requirements of Pt 4, Ch 6, 7 Longitudinal and transverse bulkheads of integral cargo tanks for tank bulkhead plating. Otherwise the plating of the inner skin is to comply with the requirements for deep tank or watertight bulkheads, as applicable, see Pt 3, Ch 7 Bulkheads.

3.11.2 For details regarding the accessibility and the standard required width of the double skin on Type C tankers, reference is made to Pt 4, Ch 4, 3.6 Special requirements for Type C tankers. Requirements are also given for strengthening the double skin in cases where the width is reduced to the minimum value as allowed by the ADN. In this case, the required percentages of increase in thicknesses of the deck, sideshell and sheerstrake plating as given in Pt 4, Ch 4, 3.6 Special requirements for Type C tankers are to be applied to the minimum values as calculated by using this Chapter.

3.11.3 For details regarding the accessibility and the standard required width of the double skin on Type N tankers reference is made to Pt 4, Ch 4, 3.7 Special requirements for Type N tankers.