Section 3 Turret structures

3.1.1 Turret structures supporting multi-point mooring line arrangements are to be assessed for the maximum combined forces to which they may be subjected to in service. The turret structure is to be suitable for the appropriate maximum single-point mooring line loads and in addition the critical mooring line group loadings.

3.1.2 Environmental criteria and loading are in general to be in accordance with Pt 10 SHIP UNITS.

3.1.3 Account is to be taken of wave slamming effects, where appropriate.

3.1.4 When an internal turret is designed as a stiffened shell, the scantlings of plating and stiffeners are not to be less than required by Table 7.7.1 in Pt 4, Ch 6 Local Strength as a deep tank bulkhead, using a load head measured vertically from the point of consideration to the top of the turret well.

3.1.5 Permissible stresses for direct calculations are to be in accordance with Pt 4, Ch 5, 2 Permissible stresses.

3.1.6 The sealing arrangements, where fitted, between internal turrets and circumturret well bulkheads will be specially considered.

3.1.7 The turret structure, including structural supports in way of bearings and highly stressed structural elements of mooring line attachments, chain stoppers and supporting structures, are to be assessed for local strength as required in Part 10 and for fatigue damage due to cyclic loading in accordance with Pt 4, Ch 5, 5 Fatigue design.

3.1.8 Suitable access arrangements are to be provided to allow inspection and maintenance of turret structural and mooring system components during service. A planned procedure for the inspection of the structure and mooring system components is to be provided, as required by List of abbreviations.

3.1.9 Special consideration is to be given in design to load transfer together with the effect of hull deformations at the interface of the turret support structure with the main hull structure.

3.1.10 The scantlings of the circumturret well bulkheads, turret support arrangements and hull backup structure are to be in accordance with Pt 10 SHIP UNITS.

3.1.11 For mechanical items such as bearings and swivels see Pt 3, Ch 13, 6 Mechanical items.

3.1.12 The structure of hawsepipes and their supports is to be designed to withstand the imposed static and dynamic loads. Plating and framing in way of hawsepipes are to be reinforced as necessary. All relevant loads as defined in Chapter 3 are to be considered and the permissible stresses due to overall and local effects are to be in accordance with Pt 4, Ch 5, 2 Permissible stresses.

3.1.13 Hawsepipe components are to be of ample thickness and of a suitable size and arrangement to house the mooring cables efficiently. Due consideration is to be given, as far as practicable, to minimise the effects bending and chafing on the mooring cables.