Section 4 Single and double bottom structure

4.1.1 This Section applies to transversely and longitudinally framed bottoms.

4.1.2 Where a machinery space is situated in the aft ship, the bottom is generally to be transversely framed. Elsewhere the transverse or longitudinal framing may be adopted.

4.1.3 Care is to be taken that the rigidity of the bottom structure is not impaired by discontinuities such as recesses, lightening holes and large drain holes.

4.1.4 Floors and girders are not to be flanged, but provided with welded face bars.

4.2.1 Where the bottom is transversely framed, plate floors are to be fitted at every frame and the scantlings are to comply with the requirements of Table 6.4.1 Bottom construction in the machinery space. The thickness of the floors in way of the engine seating is also to comply with the requirements of Pt 3, Ch 6, 5.2 Seats for main propulsion engines.

Table 6.4.1 Bottom construction in the machinery space

Item	Parameter	Scantlings
Transverse framing system
Floors (single bottom)	Web depth at centreline	d f = 50l f mm
	Modulus	Z = 7,2 × k × D1 × s × l f 2 cm3
	Web thickness	t = (0,01d f + 2) mm
Floors (double bottom)	Web thickness	t = (0,008d f + 2) mm
Longitudinal framing system
Bottom transverses	Modulus	Z = 10 × k × D 1 × S × l e 2 cm3
	Web thickness	t = (0,01d f + 2) mm
Floors (double bottom)	Web thickness	t = (0,01d f + 2) mm
Transverse and longitudinal framing system
Bottom shell plating in way of engine seating	Minimum thickness	t = (0,03A + 4,5) mm
Symbols
D, T, S, s and Z are as defined in Pt 3, Ch 6, 1.3 Symbols and definitions 1.3.1 df = depth of floor at centreline, in mm le = span of bottom transverse, in metres lf = span of the floor, in metres, and is normally the breadth of the ship measured on top of the floor under consideration. If longitudinal bulkheads or equivalent floor supports are provided, an equivalent breadth may be used, but this should be not less than 0,4B A = area of engine seating top plate, in cm2, as required by Table 6.5.1 Seats for engines D1 = D, but need not be taken greater than T + 0,4 m for Zone 3, T + 0,7 m for Zone 2, T + 1,0 m for Zone 1 k = higher tensile steel factor, see Pt 3, Ch 2, 1.3 Steel 1.3.3

4.2.2 Where the bottom amidships is longitudinally framed, the bottom transverses or plate floors in a double bottom abreast the engine seating are to be spaced not more than 1,8 m apart and the thickness is to comply with the requirements of Table 6.4.1 Bottom construction in the machinery space. In way of the engine seating, floors are to be fitted at every frame and the thickness is to comply with Pt 3, Ch 6, 5.2 Seats for main propulsion engines, see also Figure 6.4.1 Engine room bottom with longitudinal framing.

Figure 6.4.1 Engine room bottom with longitudinal framing

4.2.3 The transverse strength of the bottom is also to be maintained when the bottom construction is recessed under the engines.

4.2.4 The centre girder, if required, may be omitted where the engine girders are situated less than 1,5 m from the centreline of the ship, but a docking girder should generally be fitted. Side girders are to be fitted when normally required in the same position.

4.3.1 The bottom plating in machinery spaces is to be as required in Pt 3, Ch 5 Fore End and Aft End Structure or as in the relevant ship type Chapter in Pt 4 Ship Structures (Ship Types), but the plating in way of the engine seatings is to be not less than required in Table 6.4.1 Bottom construction in the machinery space. When the thickness of the bottom plating is to be increased to meet this requirement, the increased plating is to extend for at least two frame spaces beyond the full length of the engine seating and for 1 m on either side of the seating girders.

4.4.1 Water inlets and other openings such as openings for cooler boxes are to have well rounded corners. The thickness of water inlet and cooler box plating is to be 4 mm greater than the adjacent shell plating, or 12 mm, whichever is the greater. Suitable cathodic protection is to be provided inside the cooler boxes.