Section 5 Single bottom structure and appendages

5.1.1 Unless otherwise specified in this Section, the scantlings and arrangements for single bottom structure and appendages are to be determined in accordance with the procedures described in, or as required by, Pt 7, Ch 3, 5 Single bottom structure and appendages for mono-hull craft using the pressures from Pt 5 Design and Load Criteria appropriate to multi-hulls.

5.1.2 The thickness of single bottom structural members is in no case to be less than the appropriate minimum requirement given in Pt 7, Ch 4, 2 Minimum thickness requirements.

5.1.3 Where alternatives to the requirements of Pt 7, Ch 4, 5.1 General 5.1.1 and Pt 7, Ch 4, 5.1 General 5.1.2 are proposed, they will be specially considered, provided that calculations are submitted to demonstrate that the proposed alternatives have adequate strength, rigidity and stability to resist all anticipated design loadings.

5.2.1 The scantlings and arrangements of plate keels are to be in accordance with Pt 7, Ch 4, 3.2 Keel plates.

5.2.2 Where a bar keel is fitted, the scantlings are to be sufficient to withstand the forces imposed by dry-docking the craft.

5.3.1 Centreline girders are generally to be fitted throughout the length of each hull for dry-docking or where the breadth of floors at the upper edge is greater than 1,5 m. They are generally to be fitted in association with transverse frames or transverse web frames supporting longitudinals.

5.3.2 Centreline girders may be formed with intercostal or continuous plate webs. In all cases the face flat is to be continuous. Where girder webs are intercostal, additional bracketing and local reinforcement are to be provided to maintain the continuity of structural strength.

5.3.3 The geometric section properties of the girder webs are to be in accordance with Pt 7, Ch 3, 1.18 Geometric properties and proportions of stiffener sections.

5.3.4 The face flat thickness is to be not less than the thickness of the web. The ratio of the width to thickness of the face flat is to be not less than eight but is not to exceed 16.

5.3.5 Centreline girders are to comply with the requirements of Pt 7, Ch 4, 4.8 Bottom inboard longitudinal primary stiffeners. The girder is to have adequate resistance to buckling and in some cases web stiffeners may be required.

5.4.1 Where the floor breadth at the upper edge exceeds 4,0 m, side girders are to be fitted at each side of the centreline girder such that the spacing between the side and centreline girders or between the side girders themselves is not greater than 2 m. Side girders where fitted are to extend as far forward and aft as practicable and are, in general, to be scarfed into the bottom structure forward and aft of the support at which they terminate, i.e. terminate in way of bulkheads, deep floors or other primary transverse structure.

5.4.2 The geometric section properties of the girders are to be in accordance with Pt 7, Ch 3, 1.18 Geometric properties and proportions of stiffener sections. The girder webs and face flats are to have adequate resistance to buckling.

5.4.3 The face flat thickness is to be not less than the thickness of the web. The ratio of the width to thickness of the face flat is to be not less than eight but is not to exceed 16.

5.4.4 Side girders are to comply with the requirements of Pt 7, Ch 4, 4.8 Bottom inboard longitudinal primary stiffeners. The girders are to have adequate resistance to buckling and web stiffeners may be required.

5.4.5 Watertight side girders, and side girders forming the boundaries of tank spaces, are to comply with the requirements for watertight bulkheads and deeptanks as detailed in Pt 7, Ch 3, 7.2 Watertight bulkhead plating and Pt 7, Ch 3, 7.4 Deep tank plating respectively.

5.4.6 In the engine room, additional side girders are generally to be fitted in way of main machinery seatings. Where fitted, they are to be integrated into the structure of the craft and extended forward and aft as far as practicable.

5.5.1 In transversely framed craft, floors are generally to be fitted at every frame and underneath each bulkhead.

5.5.2 In longitudinally framed craft, floors are, in general, to be fitted at every transverse web frame and bulkhead, and generally at a spacing not exceeding 2 m. Additional transverse floors or webs are to be fitted at half web frame spacing in way of engine seatings and thrust bearings, pillars, skegs, ballast/bilge keels and the bottom of the craft in the forefoot region.

Where L_R is defined in Pt 7, Ch 4, 1.5 Symbols and definitions 1.5.1

5.5.4 The geometric section properties of the girders are to be in accordance with Pt 7, Ch 3, 1.18 Geometric properties and proportions of stiffener sections. The girder webs and face flats are to have adequate resistance to buckling.

5.5.5 The face flat thickness is to be not less than the thickness of the web. The ratio of the width to thickness of the face flat is to be not less than eight but is not to exceed 16.

5.5.6 Bottom inboard transverse web frames are to comply with the requirements of Pt 7, Ch 4, 4.11 Bottom inboard transverse web frames. The floors are to have adequate resistance to buckling and web stiffeners may be required.

5.5.7 Floors are in general to be continuous from side to side and the tops of floors are, in general, to be level from side to side. For craft having considerable rise of floor the depth of the floor plate may require to be increased to maintain the required section modulus.

5.5.8 The floors are to provide efficient support to the stern tube(s) where applicable.

5.5.9 Watertight floors, or floors forming boundaries of tank spaces, are also to comply with the requirements for watertight bulkheads or deeptanks as detailed in Pt 7, Ch 3, 7.2 Watertight bulkhead plating and Pt 7, Ch 3, 7.4 Deep tank plating respectively.

5.6.1 Floors of increased thickness may be required in way of machinery spaces.

5.6.2 The depth and mechanical strength properties of floors between engine or gearbox girders is to be not less than that required to maintain continuity of structural integrity. The face flat area and web thickness of such reduced height floors are to be increased appropriately in order to maintain the continuity of structural strength, see also Pt 7, Ch 3, 4.12 Grouped frames.

5.7.1 The thickness of plate stems at the waterline is to comply with the requirements for plate keels as given in Pt 7, Ch 4, 3.2 Keel plates.

5.7.2 The forefoot and stem are to be additionally reinforced with floors.

5.7.3 The cross-sectional area of bar stems, A _bs, is not to be taken as less than :

k _a and L _R are as defined in Pt 7, Ch 4, 1.5 Symbols and definitions 1.5.1.