Section 4 Shell envelope framing

4.1.1 Unless otherwise specified in this Section, the scantlings and arrangements for shell envelope framing are to be determined in accordance with the procedures described in, or as required by, Pt 6, Ch 3, 3 Shell envelope plating for mono-hull craft using the pressures from Pt 3 General Requirements and Constructional Arrangements appropriate to multi-hulls.

4.1.2 The requirements in this Section apply to longitudinally and transversely framed shell envelopes.

4.2.1 Bottom outboard longitudinal stiffeners are to be supported by transverse web frames, floors, bulkheads, or other primary structure, generally spaced not more than 2 m apart.

4.2.2 Bottom outboard longitudinals are to be continuous through the supporting structures.

4.2.3 Where it is impracticable to comply with the requirements of Pt 6, Ch 4, 4.2 Bottom outboard longitudinal stiffeners 4.2.2, or where it is proposed to terminate the bottom outboard longitudinals in way of the transom, bulkheads or integral tank boundaries, all longitudinals are to be bracketed in way of their end connections to maintain the continuity of structural strength. Particular attention is to be taken to ensure accurate alignment of the brackets.

4.2.4 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (b).

4.3.1 Bottom outboard longitudinal primary stiffeners are to be supported by deep transverse web frames, floors, bulkheads, or other primary structures, generally spaced not more than 4 m apart.

4.3.2 Bottom outboard longitudinal primary stiffeners are to be continuous through transverse bulkheads and supporting structures.

4.3.3 Where it is impracticable to comply with the requirements of Pt 6, Ch 4, 4.3 Bottom outboard longitudinal primary stiffeners 4.3.2, or where it is proposed to terminate the stiffeners in way of the transom, bulkheads or integral tank boundaries, they are to be bracketed in way of their end connections to maintain the continuity of structural strength. Particular care is to be taken to ensure accurate alignment of the brackets. All brackets are to be `soft toed' and are to terminate on suitable supporting structure capable of carrying the transmitted bending moment.

4.3.4 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (a).

4.4.1 Bottom outboard transverse stiffeners are defined as local stiffening members which support the bottom shell and which may be continuous or intercostal.

4.4.2 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (b).

4.5.1 Bottom outboard transverse frames are defined as stiffening members which support the bottom shell. They are to be effectively continuous and bracketed at their end connections to side frames and bottom floors as appropriate.

4.5.2 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (a).

4.6.1 Bottom outboard transverse web frames are defined as primary stiffening members which support bottom shell longitudinals. They are to be continuous and substantially bracketed at their end connections to side web frames and bottom floors.

4.6.2 Where it is impracticable to comply with the requirements of Pt 6, Ch 4, 4.6 Bottom outboard transverse web frames 4.6.1, or where it is proposed to terminate the web frames in way of bulkheads or integral tank boundaries, they are to be bracketed in way of their end connections to maintain the continuity of structural strength. Particular attention is to be taken to ensure accurate alignment of the brackets. All brackets are to be `soft toed' and are to terminate on suitable supporting structure capable of carrying the transmitted bending moment.

4.6.3 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (a).

4.7.1 The scantlings and arrangements for bottom inboard longitudinal stiffeners are to be determined in accordance with the procedures described in Pt 6, Ch 4, 4.2 Bottom outboard longitudinal stiffeners using the bottom inboard stiffening member design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

4.8.1 The scantlings and arrangements for bottom inboard longitudinal primary stiffeners are to be determined in accordance with the procedures described in Pt 6, Ch 4, 4.3 Bottom outboard longitudinal primary stiffeners using the bottom inboard stiffening member design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

4.9.1 The scantlings and arrangements for bottom inboard transverse stiffeners are to be determined in accordance with the procedures described in Pt 6, Ch 4, 4.4 Bottom outboard transverse stiffeners using the bottom inboard stiffening member design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

4.10.1 The scantlings and arrangements for bottom inboard transverse frames are to be determined in accordance with the procedures described in Pt 6, Ch 4, 4.5 Bottom outboard transverse frames using the bottom inboard stiffening member design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

4.11.1 The scantlings and arrangements for bottom inboard transverse frames are to be determined in accordance with the procedures described in Pt 6, Ch 4, 4.6 Bottom outboard transverse web frames using the bottom inboard stiffening design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

4.12.1 The side outboard longitudinal stiffeners are to be supported by transverse web frames, bulkheads, or other primary structure, generally spaced not more than 2 m apart.

4.12.2 Side outboard longitudinals are to be continuous through the supporting structures.

4.12.3 Where it is impracticable to comply with the requirements of Pt 6, Ch 4, 4.12 Side outboard longitudinal stiffeners 4.12.2, or where it is proposed to terminate the side outboard longitudinals in way of the transom, bulkheads or integral tank boundaries, they are to be bracketed in way of their end connections to maintain the continuity of structural strength. Particular attention is to be taken to ensure accurate alignment of the brackets.

4.12.4 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficientsin Chapter 3 for the load model (b).

4.13.1 Side outboard longitudinal primary stiffeners are to be supported by side transverse web frames, bulkheads, or other primary structure, generally spaced not more than 4 m apart.

4.13.2 Side outboard longitudinal primary stiffeners are to be continuous through transverse bulkheads and supporting structures.

4.13.3 Where it is impracticable to comply with the requirements of Pt 6, Ch 4, 4.13 Side outboard longitudinal primary stiffeners 4.13.2, or where it is proposed to terminate the side outboard longitudinals in way of the transom, bulkheads or integral tank boundaries, they are to be bracketed in way of their end connections to maintain the continuity of structural strength. Particular care is to be taken to ensure accurate alignment of the brackets. All brackets are to be `soft toed' and are to terminate on suitable supporting structure capable of carrying the transmitted bending moment.

4.13.4 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficientsin Chapter 3 for the load model (a).

4.14.1 Side outboard transverse stiffeners are defined as local stiffening members supporting the side shell and may be continuous or intercostal.

4.14.2 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (b).

4.15.1 Side outboard transverse frames are defined as stiffening members supporting the side shell and spanning continuously between bottom floors/frames and decks. They are to be effectively constrained against rotation at their end connections.

4.15.2 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (a).

4.16.1 Side outboard transverse web frames are defined as primary stiffening members which support side shell longitudinals. They are to be continuous and substantially bracketed at their head and heel connections to deck beams and bottom web frames respectively.

4.16.2 Where it is impracticable to comply with the requirements of Pt 6, Ch 4, 4.16 Side outboard transverse web frames 4.16.1, or where it is proposed to terminate the side outboard longitudinals in way of bulkheads or integral tank boundaries, they are to be bracketed in way of their end connections to maintain the continuity of structural strength. Particular care is to be taken to ensure accurate alignment of the brackets. All brackets are to be `soft toed' and are to terminate on suitable supporting structure capable of carrying the transmitted bending moment.

4.16.3 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (a).

4.17.1 The scantlings and arrangements for side inboard longitudinal stiffeners are to be determined in accordance with the procedures described in Pt 6, Ch 4, 4.12 Side outboard longitudinal stiffeners using the side inboard design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

4.18.1 The scantlings and arrangements for side inboard longitudinal primary stiffeners are to be determined in accordance with the procedures described in Pt 6, Ch 4, 4.13 Side outboard longitudinal primary stiffeners using the side inboard design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

4.19.1 The scantlings and arrangements for side inboard transverse stiffeners are to be determined in accordance with the procedures described in Pt 6, Ch 4, 4.14 Side outboard transverse stiffeners using the side inboard design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

4.20.1 The scantlings and arrangements for side inboard transverse frames are to be determined in accordance with the procedures described in Pt 6, Ch 4, 4.15 Side outboard transverse frames using the side inboard design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

4.21.1 The scantlings and arrangements for side inboard transverse frames are to be determined in accordance with the procedures described in Pt 6, Ch 4, 4.16 Side outboard transverse web frames using the side inboard design pressure from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate.

4.22.1 The wet-deck longitudinal stiffeners are to be supported by transverse web frames, bulkheads, or other primary structure, generally spaced not more than 2 m apart.

4.22.2 Wet-deck longitudinals are to be continuous through the supporting structures.

4.22.3 Where it is impracticable to comply with the requirements of Pt 6, Ch 4, 4.22 Wet-deck longitudinal stiffeners 4.22.2, or where it is proposed to terminate the wet-deck longitudinals in way of the transom, bulkheads or integral tank boundaries, they are to be bracketed in way of their end connections to maintain the continuity of structural strength. Particular care is to be taken to ensure accurate alignment of the brackets.

4.22.4 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (b).

4.22.5 In no case are the scantlings and arrangements for the wet-deck longitudinal stiffeners to be taken as less than those required for the side inboard longitudinal stiffeners detailed in Pt 6, Ch 4, 4.17 Side inboard longitudinal stiffeners.

4.23.1 Wet-deck longitudinal primary stiffeners are to be supported by transverse web frames, bulkheads, or other primary structure, generally spaced not more than 4 m apart.

4.23.2 Wet-deck longitudinal primary stiffeners are to be continuous through transverse bulkheads and supporting structures.

4.23.3 Where it is impracticable to comply with the requirements of Pt 6, Ch 4, 4.23 Wet-deck longitudinal primary stiffeners 4.23.2, or where it is proposed to terminate the wet-deck longitudinals in way of the transom, bulkheads or integral tank boundaries, they are to be bracketed in way of their end connections to maintain the continuity of structural strength. Particular care is to be taken to ensure accurate alignment of the brackets. All brackets are to be `soft toed' and are to terminate on suitable supporting structure capable of carrying the transmitted bending moment.

4.23.4 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (a).

4.23.5 In no case are the scantlings and arrangements for the wet-deck longitudinal primary stiffeners to be taken as less than those required for the side inboard longitudinal primary stiffeners detailed in Pt 6, Ch 4, 4.18 Side inboard longitudinal primary stiffeners.

4.23.6 Additionally the requirements of Pt 6, Ch 6 Hull Girder Strength relating to global strength are to be complied with.

4.24.1 Wet-deck transverse stiffeners are defined as local stiffening members supporting the wet-deck and may be continuous or intercostal.

4.24.2 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (b).

4.24.3 In no case are the scantlings and arrangements for the wet-deck transverse stiffeners to be taken as less than those required for the side inboard transverse stiffeners detailed in Pt 6, Ch 4, 4.19 Side inboard transverse stiffeners.

4.25.1 Wet-deck transverse frames are defined as stiffening members which support the wet-deck. They are to be effectively continuous and bracketed at their end connections to side frames.

4.25.2 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (a).

4.25.3 In no case are the scantlings and arrangements for the `wet-deck' transverse frames to be taken as less than those required for the side inboard transverse frames detailed in Pt 6, Ch 4, 4.20 Side inboard transverse frames.

4.26.1 Wet-deck transverse web frames are defined as primary stiffening members which support wet-deck longitudinals. They are to be continuous and substantially bracketed at their end connections to side transverse web frames.

4.26.2 Where it is impracticable to comply with the requirements of Pt 6, Ch 4, 4.26 Wet-deck transverse web frames 4.26.1, or where it is proposed to terminate the wet-deck longitudinals in way of the bulkheads or integral tank boundaries, they are to be bracketed in way of their end connections to maintain the continuity of structural strength. Particular care is to be taken to ensure accurate alignment of the brackets. All brackets are to be `soft toed' and are to terminate on suitable supporting structure capable of carrying the transmitted bending moment.

4.26.3 The requirements for section modulus, inertia and web area are to be determined from the general equations given in Pt 6, Ch 3, 1.17 Stiffening general, using the design pressures from Pt 5, Ch 3, 3.1 Hull structures or Pt 5, Ch 4, 3.1 Hull structures for non-displacement or displacement craft as appropriate, and the coefficients Φ_Z, Φ_I, and Φ_A as detailed in Table 3.1.1 Section modulus, inertia and web area coefficients in Chapter 3 for the load model (a).

4.26.4 In no case are the scantlings and arrangements for the wet-deck transverse web frames to be taken as less than those required for the side inboard transverse web frames detailed in Pt 6, Ch 4, 4.21 Side inboard transverse web frames.

4.26.5 Primary transverse web frames that link the strength deck to the wet-deck structure and which carry the transverse global loading are additionally to comply with Pt 6, Ch 6, 3.4 Torsional strength.

4.26.6 Particular attention is to be taken to ensure that the continuity of transverse structural strength is maintained. All primary transverse members are to be continuous through the inboard side structure and integrated into transverse bulkheads or other primary structure within each hull (see Figure 4.4.1 End connection details, wet-deck structure). In the case of trimaran type craft the primary transverse members are to be continuous through the centre hull. Additionally the side inboard shell plating in way of the intersection is to be increased locally by not less than 50 per cent.

Figure 4.4.1 End connection details, wet-deck structure

4.27.1 Where the lower hull structure incorporates ring frames and attached shell plating fitted between bulkheads or diaphragms, the scantlings of the lower hull shell stiffening may be derived from an established method for stiffening analysis or Recognised Standard for pressure vessels using the design loading from Pt 5, Ch 4, 3.1 Hull structures Modes of failure to be considered are buckling, frame collapse, inter frame shell collapse and overall frame shell collapse between bulkheads. A copy of the direct calculations is to be submitted for consideration.

4.28.1 The scantlings of end brackets in way of transverse web frames/crossdeck primary structure which carry transverse global loading, are to be as large as practicable and be additionally reinforced as necessary. The webs of deep brackets are to be stiffened as necessary to resist buckling, see also Pt 6, Ch 6, 3.5 Strength of cross-deck structures.