Section 11 Double skin structure

11.1.1 This Section covers the arrangements and requirements for transversely and longitudinally framed side shell structures of double skin ships.

11.1.2 The scantlings of the double skin structure, except side shell plating, are to comply with Table 1.11.1 Double skin structure (General requirements). For side shell plating, see Pt 4, Ch 1, 5 Hull envelope plating.

11.1.3 The side shell may be transversely or longitudinally framed. The longitudinal bulkheads are in general to have the same framing system as the shell.

11.2.1 The lower ends of side frames and stiffeners of longitudinal bulkheads may overlap the floors or otherwise be connected to the floors or tank top by means of brackets. At their upper ends, side frames and bulkhead stiffeners are to be interconnected by means of brackets, see Figure 1.11.1 Frame arrangement (transverse framing).

11.2.2 In addition to the frames, plate webs are to be fitted spaced not more than 8 m apart, see also Figure 1.11.2 Arrangement of plate webs. Manhole openings are to be provided in the plate webs to allow for inspection. Horizontal stiffeners are to be fitted to the plate webs, spaced not more than twice the frame spacing apart. Plate webs with large access holes are to be additionally stiffened and their scantlings are to be verified by direct calculations. The scantlings of truss-type web frames, replacing plate webs and composed of rolled or built sections, are to be determined by direct calculation.

11.2.3 Alternatively, plate webs in accordance with Pt 4, Ch 1, 11.2 Transverse framing 11.2.2 may be fitted at every frame.

Table 1.11.1 Double skin structure (General requirements)

Item		Parameter	Requirement
(1)	Shell frames	Modulus	cm3
(2)	Vertical stiffeners on longitudinal bulkhead	Modulus
(3)	Brackets under deck	Depth	db as shown in Figure 1.11.1 Frame arrangement (transverse framing)
		Thickness	mm
		Flange width	mm
Longitudinal framing systems
(4)	Shell longitudinals	Modulus	cm3, see Note 1
(5)	Horizontal stiffeners on longitudinal bulkhead	Modulus	cm3, see Note 1
(6)	Web frames at shell, see Figure 1.11.3 Arrangement for web frames	Modulus	cm3
(7)	Web frames on longitudinal bulkhead, Figure 1.11.3 Arrangement for web frames	Modulus
(8)	Bracket under deck	Depth	dbas shown in Figure 1.11.1 Frame arrangement (transverse framing)
		Thickness	mm
		Flange width	m
Transverse and longitudinal framing systems
(9)	Plating of longitudinal bulkhead, see Notes 2 and 3	Thickness
(10)	Plate webs, see Figure 1.11.2 Arrangement of plate webs	Thickness	The greater of mm
(11)	Horizontal stiffeners on webs	Width	mm
		Thickness	thickness plate webs
Symbols
L, B, D, T, S, s, t, k, Z and Iare as defined in Pt 4, Ch 1, 1.5 Symbols and definitions 1.5.1
b = breadth of side shell structure, in metres, as indicated in Figure 1.11.2 Arrangement of plate webs hs = hde + ht but not less than 2,0 m hde = distance of longitudinal to the deck at side, in metres ht = 0 for void spaces = 0,50 for deep tanks but not less than the distance to the top of the overflow q = height of single or double bottom, in metres, as shown in Figure 1.11.1 Frame arrangement (transverse framing) s1 = spacing between horizontal stiffeners, in metres sd = stiffener spacing or width of double skin, whichever is the smaller		ts = thickness of side shell, in mm H1 = vertical framing depth, in metres, as shown in Figure 1.11.1 Frame arrangement (transverse framing) and Figure 1.11.2 Arrangement of plate webs L1 = L, but is to be taken as not less than 50 m nor more than 100 m Sb = spacing of plate webs, in metres h4 = ho + 0,5 b1 = the greater of the distance, in metres, from the middle of the effective length to the top of the cargo or = 1,5 m = whichever is the greatest hO = the vertical distance, in metres, from the mid-point of span of the stiffener to the highest point of the tank including hatchway b1 = the horizontal distance, in metres, from the centre line to the hatchway in way of the cargo hatch T1 = D – q, but need be taken not greater than T + 0,4 – q for Zone 3, T + 0,7 – q m for Zone 2, T + 1,0 – q m for Zone 1, in metres Zf = modulus of frame, in cm3 Zl = modulus of side shell longitudinal, in cm3 Zw = modulus of web frame, in cm3
Note 1. The web thickness of longitudinals is not to be less than 7 mm. Note 2. For bulk carriers it is recommended to add 3 mm to the thickness of the lower edge of the bulkhead over a height of about 250 mm above the inner bottom. Note 3. The thickness of the upper strake of the longitudinal bulkhead may require to be increased to satisfy the hull girder bending stress criteria in Pt 3, Ch 4 Longitudinal Strength

Figure 1.11.1 Frame arrangement (transverse framing)

11.3.1 Longitudinals on shell and longitudinal bulkheads are to be supported by web frames, spaced not more than 2,5 m apart, and efficiently connected thereto.

Figure 1.11.2 Arrangement of plate webs

Figure 1.11.3 Arrangement for web frames

11.3.2 Web frames are to be fitted in line with plate floors and are generally to be constructed as indicated in Figure 1.11.3 Arrangement for web frames. The lower ends of the web frames may overlap the floors or are otherwise to be connected to the floors or tank top by means of brackets. At their upper ends, web frames are to be interconnected by means of brackets, see also Figure 1.11.3 Arrangement for web frames.

11.3.3 In addition to the web frames as required by Pt 4, Ch 1, 11.3 Longitudinal framing 11.3.2, plate webs are to be fitted not more than 8 m apart, see also Fig. Figure 1.11.2 Arrangement of plate webs(b). Manhole openings are to be provided in the plate webs to allow for inspection. Horizontal stiffeners are to be fitted to the plate webs spaced not more than twice the frame spacing apart. Plate webs with large access holes are to be additionally stiffened and their scantlings are to be verified by direct calculations.

11.3.4 As an alternative to the web frames required by Pt 4, Ch 1, 11.3 Longitudinal framing 11.3.2, plate webs in accordance with Pt 4, Ch 1, 11.3 Longitudinal framing 11.3.3 may be fitted.

11.4.1 The scantlings of the longitudinal bulkhead are to comply withTable 1.11.1 Double skin structure (General requirements).

11.4.2 Where the longitudinal bulkhead is not connected to the bottom shell but supported by the bottom floors, vertical stiffeners are to be fitted to the floors and connected to the inner bottom plating in line with the longitudinal bulkhead.

11.4.3 The ends of the longitudinal bulkheads are to be well scarfed into the ship's fore and aft structure.

11.5.1 It is recommended that Owners consider subdividing the space between side shell and longitudinal bulkhead such that the ship remains afloat when one of the compartments becomes flooded.

11.5.2 For ships navigating on the Rhine or on European waterways with an overall length greater than 110 m, compliance with damage stability requirements are mandatory in accordance with the European Standard laying down Technical Requirements for Inland Navigation vessels (ES-TRIN).

11.5.3 For ships carrying dangerous goods, see also Pt 4, Ch 1, 12 Additional requirements for ships carrying dangerous goods.