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Conversion of “marine” cranes in “offshore” cranes

  • Comments: It is well know that there is a difference between a "marine crane" and an "offshore crane". The former is allowed to operate in sheltered waters while the latter in open sea. A marine crane is mostly intended for harbour operation and are mainly subject to ILO certification. An offshore crane, instead, is subject to dynamic forces due to waves, ship motion, vertical spring rate, type of operation (ship-to-ship, handling of submerged equipment) not considere for an ILO crane and it is more and more required to be provided with proper load chart by offshore stakeholders. Many ship-operators, involved with offshore market, have their vessels fitted with a crane wich sometime is not certified for offshore. Medea has established consolidated and approved method to derate a "pure" marine crane in an offshore crane. This is a sample.
  • Name of Project: Crane Derating for offshore operation (6.25% derating for survey, 25% for ship-to-ship)
  • Scope of Work: to define the % of the SWL to be deducted from the rated value for harbour operations
  • Reference Standards: [1] Rules for Loading and Unloading Arrangements and For Other Lifting Appliances on Board Ships – Part C “Cranes for Offshore Operations” – Rina 2016, as applicable. [2] Cofe for Lifting Appliance Lifting Appliances in a Marine Environment – Section 3 “Offshore Cranes” – Lloyd’s Register 2013, as applicable.

  • OUTPUT DOCUMENTATION: Calculation spreadsheet for Dynamic Amplification Factor against sea state, issued for Class approval. Derated Load Charts.