3.3.1 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. That
is, the combination of the following loadings is to be investigated, for both intact
and damaged conditions:
- Most unfavourable hull loading among cases detailed in Pt 10, Ch 2 Loads and Load Combinations.
- Maximum mooring restoring force from the multi-point mooring line arrangement,
as substantiated by analyses according to Pt 3, Ch 10, 5 Design analysis.
- Permanent and live loads including accelerations due to vessel motions and sea
pressures acting on the turret. Account is to be taken of wave slamming effects,
where appropriate.
3.3.2 A structural analysis using finite element method is required to verify that the
strength of the turret structure is sufficient. The extent of the structural model
is to be sufficient to minimise the effect of boundary conditions. Reference is
hereby made to the Appendix B of the LR ShipRight Design and Construction
Procedure for Ship Units. Permissible stresses are to be taken according to
Pt 4, Ch 5, 2 Permissible stresses.
3.3.4 The sealing arrangements, where fitted, between internal turrets and
circumturret well bulkheads will be specially considered.
3.3.5 The turret structure and supporting elements in way of bearings and other highly
stressed structural elements of the load path are to be assessed for local strength
as required in Pt 10, Ch 3 Scantling Requirements. In particular, finite element
analysis of attachments to the hull is to be carried out to ensure satisfactory
stress distribution of the mooring loads into the hull structure. Permissible stress
levels are to comply with Pt 4, Ch 5, 2 Permissible stresses. Fatigue damage
due to the cyclic loading is to be assessed in accordance with Pt 4, Ch 5, 5 Fatigue design.
3.3.7 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.
3.3.8 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.
3.3.9 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 Pt 3, Ch 3 Production and Storage Units 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.
3.3.10 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.