Section 2 Structure
Clasification Society 2024 - Version 9.40
Clasifications Register Rules and Regulations - Rules and Regulations for the Classification of Offshore Units, July 2022 - Part 3 Functional Unit Types and Special Features - Chapter 18 Crane Units - Section 2 Structure

Section 2 Structure

Parent topic: Chapter 18 Crane Units

2.1 Plans and data submission

2.1.1 In addition to the structural plans and information as required by Pt 3, Ch 1, 2 Information required and Pt 4, Ch 1, 4 Information required, additional plans are to be submitted showing:
  1. Cranes, other lifting appliances, boom rests and their supporting structures.
  2. Details of castings e.g. cast nodes for column-stabilised crane units.
  3. Fixed cargo securing fittings and arrangements.
  4. Jacket restraint structures (for the securing of jackets for transportation) and their supporting structures.
  5. Foundations and supporting structure to any major mission equipment (e.g. hydraulic power units for pile hammers and grippers).
2.1.2 The general arrangement plan of the crane unit is to include the locations of the following:
  1. Cranes, other lifting appliances, frames and boom rests.
  2. Arrangement of cranes showing slewing angles, radiuses and inclinations of the crane booms.
  3. Work, laydown and storage areas including fixed cargo securing fittings and grillages.
  4. Hatches and other openings to enclosed spaces for lifting operations.
  5. Doors, hatches, ventilation and other openings to crew accommodation, control stations, stations for crane unit operations, store rooms and workshops.
  6. Jacket restraint structures.

2.2 Structural assessment

2.2.1 The global structure is to be designed for all lifting and non-lifting modes of operation for the design load combinations defined in Pt 4, Ch 3, 4.3 Load combinations. The most unfavourable loading conditions are to be assessed, which are to be determined by considering:
  1. Single crane lifts and combined crane lifts (where more than one heavy-lift crane is installed).
  2. Lifts with maximum loads resulting from crane operations taking into account all significant load combinations, crane configurations, and crane positions (e.g. luffing angles, slewing angles).
    Note All combinations of maximum horizontal forces, vertical forces and overturning moments and slewing moments are to be considered. Reference is also made to the crane load versus radius diagrams/charts.
  3. Crane lifts in sheltered water, shallow water and deep water and the effect on the motions of the unit, as applicable.
  4. The stages/sequence of crane unit operations, set-down and transportation, which are to be defined.
  5. Limits of stability.
  6. The range of draughts and metacentric heights (GM).
    Note Lifting at shallow draughts may result in higher global loads. A large GM may result in a higher pitch and roll accelerations with higher forces acting on the securing devices.
  7. Load cases with and without heavy payload on deck.
    Note Load cases without heavy payload may have higher hydrostatic loads to maintain the same draught.
  8. The effect of wind heeling.
  9. Coupled dynamics of the unit, the barge from which the object is lifted and the object itself, as applicable.
  10. The type of objects to be lifted and whether the lifts take place in air, in water or through both.
  11. Survival and transit conditions including the transportation of payload on deck.
  12. Tank loading patterns.
  13. Float-on float-off loading conditions, as applicable.
  14. Roll-on roll-off loading conditions, as applicable.
  15. Skid-on skid-off loading conditions, as applicable.
  16. Any other foreseeable operational or emergency scenarios and related loads and loading conditions (e.g. gross overload, emergency load release).

    Where it is demonstrated that accidental loads only cause local damage, global strength need not be investigated for loading condition (c) in Pt 4, Ch 3, 4.3 Load combinations.

2.2.2 Jacket removal and transport load cases are to consider:
  1. All structural and non-structural jacket items.
  2. Rigging arrangements.
  3. The degrees of freedom at the jacket restraints.
  4. Spring stiffness for the jacket restraints, crane tips and boom.

2.2.3 The model test programme is to consider all lifting and non-lifting modes of operation, see Pt 4, Ch 1, 4.6 Model test specifications and reporting.

2.2.4 The design loadings for the strength of areas for working, laydown, storage and the structure supporting any major mission equipment, e.g. hydraulic power units, are to be defined by the designers/Builders. Calculations are to be submitted for the design loadings, including the effect of vessel deflections.

2.2.5 Dynamic lifting cases are to include hook load dynamic amplification (hoisting) factors which are to be applied to the lifted object and its rigging.

2.2.6 The limiting environmental criteria for each lifting case are to be specified by the Owner as operability curves (significant wave height versus peak period) with associated wind conditions and vessel heading relative to the directions of wind and waves. Any associated limiting criteria for each lifting case are also to be specified, e.g. crane boom positions and slew angle, heel and trim of the crane unit and the motions of the unit or barge to or from where the object is lifted.

2.2.7 Where the global structure is designed to lifting cases with lifting loads less than the safe working loads of the crane, restrictions are to be recorded in the Operations Manual and on the load versus radius diagrams/charts.

2.2.8 The return periods of the environmental parameters for non-lifting load cases (for design load combinations (b) and (d) defined in Pt 4, Ch 3, 4.3 Load combinations) are specified in Table 18.2.1 Return periods of the environmental parameters for non-lifting dynamic load cases for the respective loading condition.

Table 18.2.1 Return periods of the environmental parameters for non-lifting dynamic load cases

Loading condition

(mode of operation)

Return period for load cases (b) and (d)
Operating – Non-lifting 1 year, see Note 1
Inspection/maintenance 1 year
Survival 50 years
Transit 25 years
Note 1. Where requested by the Owner/designer, a return period longer than 1 year may be used.

2.2.9 For work, laydown and storage areas subject to heavy wear, e.g. dragging lifting gear, a thickness allowance to account for wear in addition to the corrosion allowance required by Pt 4, Ch 3, 7 Corrosion additions is recommended.

2.3 Materials

2.3.1 Crane pedestals, boom rests and their support structures are to be divided into the following categories defined in Pt 4, Ch 2, 2.1 General 2.1.2:

  • Special structure.
  • Primary structure.
  • Secondary structure.

2.4 Offshore containers

2.4.1 Offshore containers are to comply with Pt 3, Ch 4, 2.4 Offshore containers.

Copyright 2022 Clasifications Register Group Limited, International Maritime Organization, International Labour Organization or Maritime and Coastguard Agency. All rights reserved. Clasifications Register Group Limited, its affiliates and subsidiaries and their respective officers, employees or agents are, individually and collectively, referred to in this clause as 'Clasifications Register'. Clasifications Register assumes no responsibility and shall not be liable to any person for any loss, damage or expense caused by reliance on the information or advice in this document or howsoever provided, unless that person has signed a contract with the relevant Clasifications Register entity for the provision of this information or advice and in that case any responsibility or liability is exclusively on the terms and conditions set out in that contract.