Surface units
Clasification Society 2024 - Version 9.40
Statutory Documents - IMO Publications and Documents - International Codes - 1989 MODU Code – Code for the Construction and Equipment of Mobile Offshore Drilling Units, 1989 – Resolution A.649(16) - Chapter 3 – Subdivision, Stability and Freeboard - 3.7 Freeboard - Surface units

Surface units

  3.7.7 Load lines should be assigned to surface units as calculated under the terms of the 1966 Load Line Convention and should be subject to all the conditions of assignment of that Convention.

  3.7.8 Where it is necessary to assign a greater than minimum freeboard to meet intact or damage stability requirements or on account of any other restriction imposed by the Administration, regulation 6(6) of the 1966 Load Line Convention should apply. When such a freeboard is assigned, seasonal marks above the centre of the ring should not be marked and any seasonal marks below the centre of the ring should be marked. If a unit is assigned a greater than minimum freeboard at the request of the owner, regulation 6(6) need not apply.

  3.7.9 Where moonpools are arranged within the hull in open communication with the sea, the volume of the moonpool should not be included in the calculation of any hydrostatic properties. If the moonpool has a larger cross-sectional area above the waterline at 0.85D than below, an addition should be made to the geometric freeboard corresponding to the lost buoyancy. This addition for the excess portion above the waterline at 0.85D should be made as prescribed below for wells or recesses. If an enclosed superstructure contains part of the moonpool, deduction should be made for the effective length of the superstructure. Where open wells or recesses are arranged in the freeboard deck, a correction equal to the volume of the well or recess to the freeboard deck divided by the waterplane area at 0.85D should be made to the freeboard obtained after all other corrections,except bow height correction, have been made. Free surface effects of the flooded well or recess should be taken into account in stability calculations.

  3.7.10 The procedure described in 3.7.9 should also apply in cases of small notches or relatively narrow cut-outs at the stern of the unit.

  3.7.11 Narrow wing extensions at the stern of the unit should be considered as appendages and excluded for the determination of length (L) and for the calculation of freeboards. The Administration should determine the effect of such wing extensions with regard to the requirements for the strength of unit based upon length (L).


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