2.6 Special considerations for column stabilized units
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Statutory Documents - IMO Publications and Documents - International Codes - 1979 MODU Code – Code for the Construction and Equipment of Mobile Offshore Drilling Units – Resolution A.414(XI) - Chapter 2 – Construction, Strength and Materials - 2.6 Special considerations for column stabilized units

2.6 Special considerations for column stabilized units

  2.6.1

  • .1 Unless deck structures are designed for wave impact, a clearance acceptable to the Administration should be maintained between passing wave crests and the deck structure. The Administration should be provided with model test data, past operating experience with similar configurations or calculations showing that adequate provision is made to maintain this clearance.

  • .2 For units operating while supported by the sea-bed the clearance required in 2.5.1.2 should be maintained.

  2.6.2

  • .1 The scantlings of the upper structure should not be less than those required for the loadings shown in the deck loading plan.

  • .2 When an approved mode of operation or damaged condition in accordance with the stability requirements allows the upper structure to become waterborne, special consideration should be given to the resulting structural loadings.

  2.6.3

  • .1 The scantlings of columns, lower hulls and footings should be based on the evaluation of hydrostatic pressure loadings and combined loadings including wave and current considerations.

  • .2 Where a column, lower hull or footing is a part of the overall structural frame of a unit, consideration should also be given to stresses resulting from deflections due to the applicable combined loadings.

  • .3 Particular consideration should be given to structural arrangements and details in areas subject to high local loadings resulting from, for example, external damage, wave impact, partially filled tanks or bottom bearing operations.

  • .4 When a unit is designed for operations while supported by the sea-bed, the footings should be designed to withstand the shock of bottom contact due to wave action on the hull. Such units shouId also be evaluated for the effects of possible scouring action (loss of bottom support). The effect of skirt plates, where provided, should be given special consideration.

  • .5 The structure in way of components for the position mooring system such as fairleads and winches should be designed to withstand the stresses imposed when a mooring line is loaded to its breaking strength.

  2.6.4

  • .1 Bracing members should be designed to make the structure effective against applicable combined loadings, and when the unit is supported by the sea-bed, against the possibility of uneven bottom bearing loadings. Bracing members should also be investigated, where applicable, for combined stresses including local bending stresses due to buoyancy, wave forces and current forces.

  • .2 Where applicable, consideration should be given to local stresses caused by wave impact.

  • .3 Where bracings are watertight they should be designed to prevent collapse from hydrostatic pressure.

  • .4 Consideration should be given to the need for ring frames to maintain stiffness and shape in tubular bracing members.

Parent topic: Chapter 2 – Construction, Strength and Materials
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