Section 2 Sea bed-stabilised units

2.1.1 This Section outlines the structural design requirements of sea bed-stabilised units as defined in Pt 1, Ch 2, 1 Conditions for classification. Additional requirements for particular unit types related to the design function of the unit are given in Pt 4, Ch 4, 3 Self-elevating units Pt 3 Functional Unit Types and Special Features. Self-elevating units are to comply with Pt 4, Ch 4, 3 Self-elevating units.

2.1.2 Units of this type are generally designed to operate under normal operating environmental conditions and severe storm conditions whilst resting on the sea bed. The design transit condition and design limitations are to be specified by the Owner/designer.

2.1.3 The structural analysis and determination of scantlings is to be on the basis of distribution of loadings and ballast required to satisfy Pt 4, Ch 4, 2.1 General 2.1.2 and all units are to have adequate reserve of bearing pressure on the support footings, pontoons or mats.

2.1.4 The requirements of Pt 4, Ch 4, 1 Column-stabilised units and Pt 4, Ch 4, 3 Self-elevating units are to be complied with as applicable to the design of the unit.

2.1.5 The permissible stress levels in all operating modes are to comply with Pt 4, Ch 5 Primary Hull Strength.

2.1.6 The minimum local scantlings are to comply with the requirements of Pt 4, Ch 6 Local Strength, for column-stabilised units as applicable, but the bottom structure should not be less than required for tank bulkheads in Pt 4, Ch 6 Local Strength using the load head equivalent to the maximum design bearing pressure. In general, bottom primary members supporting shell stiffeners are to be spaced not more than 1,85 m apart and side girders or equivalent are to be spaced 2,2 m apart. The buckling strength of the primary member webs is to be in accordance with Pt 4, Ch 5 Primary Hull Strength, see also Pt 4, Ch 4, 2.4 Corrosion protection.

2.2.1 For on-bottom modes of operation, the clearance air gap between the underside of the deck structure and the highest predicted design wave crest is to be in accordance with Pt 4, Ch 4, 3.2 Air gap. In transit conditions, the air gap is to be in accordance with Pt 4, Ch 4, 1.2 Air gap. Calculations, model test results or prototype reports are to be submitted for consideration.

2.3.1 Classification will be based upon the Owner’s/designer’s assumptions in operating the unit and the sea bed conditions. These assumptions are to be recorded in the Operations Manual. It is the responsibility of the Operator to ensure that actual conditions do not impose more severe loadings on the unit.

2.3.2 Procedures and limitations for ballasting and re-floating the unit in order to avoid overstressing the structure by static or dynamic loads are to be clearly defined in the Operations Manual, see Pt 3, Ch 1, 3 Operations manual.

2.4.1 The corrosion allowance for wastage and the means of protection are to be to the satisfaction of LR and are to be agreed at the design stage.

2.4.2 The general requirements for corrosion protection are to comply with Pt 8 Corrosion Control.