Section 4 Movable decks

4.1.1 Movable decks other than those described in Pt 8, Ch 5, 4.1 Classification 4.1.2 are not a classification item, although consideration is to be given to the associated supporting structure. Where movable decks are fitted, it is recommended that they are to be based on the requirements of this Section.

4.1.2 At the Owner's or Builder's request, however, movable decks will be included as a classification item, and the class notation movable decks will be entered in the Register Book. In such cases, all movable decks on board the craft are to comply with the requirements of this Section.

4.2.1 Movable decks are generally to be constructed as pontoons comprising a web structure with top decking. Other forms of construction will be individually considered.

4.2.2 Positive means of control are to be provided to secure decks in the lowered position.

4.2.3 The decks are to be efficiently supported, and hinges, pillars, chains or other means (or a combination of these) are to be designed on the basis of the imposed loads. Where supporting chains and fittings are required, they are to have a factor of safety of at least two on the proof load.

4.2.4 Plans showing the proposed scantlings and arrangements of the system are to be submitted.

4.2.5 Where it is proposed to stow the pontoons on deck, when not in use, details of the proposals for racks, fittings, etc. are to be submitted for consideration.

4.3.1 The loading requirements for movable decks are to be in accordance with Pt 8, Ch 5, 3.1 General.

4.3.2 Where it is proposed also to use the decks for general cargo, the design loadings are to be submitted for consideration.

4.4.1 The scantlings and arrangements of movable decks are to be not less than required by the Rules for the supporting structure in which they are fitted. In general the end fixity of primary stiffening members is to be taken as simply supported. Local and secondary stiffening members may be either partially or fully fixed at their end connections dependent upon the proposed arrangement.

4.5.1 Where wheeled vehicles are to be used, the supporting arrangements are to be such that the movement at the edge of one pontoon relative to the next does not exceed 50 mm during loading or unloading operations.

4.6.1 As an alternative to the requirements of Pt 8, Ch 5, 4.3 Loading, the structure may be designed on the basis of a direct calculation using a grillage idealisation. The method adopted and the stress levels proposed for the material of construction are to be submitted for consideration, see also Pt 3, Ch 1, 2 Direct calculations.