Section 2 Structural design
Clasification Society 2024 - Version 9.40
Clasifications Register Guidance Information - Guidance Notes for Nearshore Hull Structures, April 2021 - Chapter 2 Hull Structure Design - Section 2 Structural design

Section 2 Structural design

Parent topic: Chapter 2 Hull Structure Design

2.1 Strength

2.1.1 Either the design loads required by the Rules with the ship service factor or the direct calculation results obtained from Ch 2, 1 Design loads can be used for local scantling and strength assessment.

2.1.2 In general, class is suspended during a towed voyage. If it is agreed for a ship to maintain class during a towed voyage with the Classification Group, the voyage condition is to be considered akin to transit voyage for scantling and strength assessment.

2.1.3 Nearshore units operating at fixed locations may require additional accidental cases to the Rule requirements or additional design evaluations for hazards identified by risk assessments at the request of the Owner. Where tsunami is likely to occur at the location of operation, especially if the vessel or other facility in proximity contains dangerous cargo, safety measures including evacuation are to be prepared by a risk assessment.

2.1.4 For the units having liquefied gas cargo containment systems, the site-specific accelerations used for dynamic liquid pressure in accordance with Part G - Guidance in the Rules and Regulations for the Construction and Classification of Ships for the Carriage of Liquefied Gases in Bulk, July 2022 can be derived by the direct calculation. In this case, limiting the direct calculation results in Ch 2, 1.3 Direct calculations 1.3.2 may not apply for this purpose only. Since the cargo tanks may not be emptied during emergency escapes, the combination of maximum vapour pressure and the liquid pressure should be considered for the worst-case scenario of the emergency escape condition. If cargo may be carried during the transit condition, the internal pressure should be taken into account.

2.1.5 For the majority of nearshore units, the transit condition for strength assessment will be dominant over the on-site operation. Any waiver of the bow impact reinforcement of the ships classed for Protected waters service or Extended protected waters service in accordance with Pt 3, Ch 5, 1.5 Strengthening of bottom forward in the Rules and Regulations for the Classification of Ships, July 2022 is only applicable if the transit voyage will be undertaken in reasonable weather.

2.2 Fatigue

2.2.1 Fatigue assessment for site-specific operations is to be carried out using the appropriate combination of the following:
  • fatigue due to environmental loads during transit and on-site operation;
  • fatigue due to loading and unloading (low cycle fatigue).

2.2.2 For on-site fatigue assessment, a minimum of five years of historical sea-state data should be analysed.

2.2.3 If the relative heading angle to incoming waves will be limited due to wave transformation or weather-vaning properties, the actual or the most probable heading angles shall be used.

2.2.4 The fatigue assessment of nearshore units can be carried out in accordance with Ch 1, 7 Fatigue Design Assessment Overview to Ch 1, 10 Level 3 Fatigue Assessment in the ShipRight Procedure for Ship Units.

2.3 Sloshing

2.3.1 In general, the return period of 100 years is to be used for the sloshing assessment of a permanent installation unless the design life of the system is substantially lower than 20 years. The return period may be reduced for units planning to escape under extreme weather.

2.3.2 For nearshore units carrying liquefied gas cargo, unrestricted filling levels are to be considered. Guidance about membrane tanks related to nearshore operations can be found in the following documents:
  • ShipRight Procedure for Sloshing Assessment Guidance Document for Membrane Tank LNG Operations;
  • Guidance on the Operation of Membrane LNG Ships to Reduce the Risk of Damage Due to Sloshing, 6. Terminals in exposed locations and floating LNG terminals.
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