Bulk+Carrier+CSR

Bulk Carriers built according to the Common Structural Rules.

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Purpose

To establish requirements for reducing the risks of structural failure in order to help safeguard life, property and the environment. The rules also aim to provide requirements to ensure the adequate durability of the hull structure for the design life.

Benefits

The CSR for Bulk Carriers will:

  • ensure that vessels meeting the new standard will be recognised by the industry as being at least as safe, robust and fit for purpose as would have been required by any of the existing Rules

  • ensure sufficient durability throughout the operational life in terms of corrosion margins and fatigue strength

  • define the minimum structural state at which steel renewal is required in order to continue safe operation

Features

The Common Structural Rules (CSR) are applicable to Bulk Carriers with lengths > 90 metres, and Bulk Carriers built according to these rules will be assigned the additional class notation CSR.

The most important design basis for the CSR is the 25-year design life. Although this has not previously been stated explicitly, the classification societies have based their existing rules on a 20-year design life. The 25-year design life in CSR makes a difference with respect to loads, fatigue, corrosion and coating.

All calculations are based on a North Atlantic wave environment, which is expected to be the harshest environment the Bulk Carrier will trade in.

All the dynamic loads are based on a 10-8 probability level of exceedance and all stresses are calculated using net thickness wfrom which the corrosion addition has been removed.

A new requirement for the assessment of the ultimate capacity of hull girders has been developed and is introduced in the CSR for both sagging and hogging conditions. This requirement results in a clearer safety margin for this major failure mode.

The typical fatigue strength of a longitudinal at a bracket connection, connection of hopper plate to inner bottom plate, lower stool plate to inner bottom plate, transverse corrugated bulkhead connection to lower stool top plate, and side frame lower bracket toe will in CSR be designed based on a 25-year design fatigue life in a North Atlantic wave environment.

Process

Follows the ordinary approval process for newbuildings and covers only Hull approval.

Ships built to the Common Structural Rules (CSR) will be safer than ships built to existing rules because:

  • The calculations are performed on the net thickness. The existing rules verify the gross scantlings and allow for a 20-25% reduction in gross scantlings during operation, whereas the CSR directly and explicitly verify the thickness required during the operation of the vessel.

  • The net required thickness, which is the thickness at which renewal is required, has been increased. Consequently, the probability of failures related to buckling and yield is reduced.

  • The minimum fatigue standard has been significantly increased and additional requirements for design details have been introduced. Consequently the probability of cracks and pollution has been significantly reduced.

Ships built to the CSR will be more robust than vessels built to existing rules because:

  • corrosion margins are redistributed and increased for strength elements located in areas prone to corrosion

  • following the inclusion of the coating performance standard, the actual coating is expected to last longer than for existing vessels

  • the increased fatigue standard and structural detail design requirements will reduce the number of cracks

  • the increased net and gross scantling will reduce the need for buckling and yield related repairs

The scope of the rules has been extended by requiring:

  • a significant increase in the number of load cases

  • mandatory assessment of the hull girder ultimate strength

  • an increased number of details assessed by fine mesh FEM

The rules provide more accurate and physically correct results through:

  • a new load model giving a more physically correct representation of the loads the vessel will encounter

  • coherent acceptance criteria and load levels - static and extreme wave loads

  • the incorporation of state-of-the-art buckling assessment tools

  • a more advanced finite element procedure