The International Association of Classifications Societies (IACS) has announced the adoption of new Unified Requirements to further improve the safety of Large Container Ships.
The requirements will enhance consistency between pre-existing Class Society provisions in this area. There are three new safety measures that are incorporated into a single new Unified Requirement (UR S11A). IACS says these safety measures provide a robust, timely, and complete response to the findings of the investigation by Japan’s Ministry of Land, Infrastructure, Transport, and Tourism (MLIT) issued in March 2015 and subsequent papers to the IMO. The UR S11A is a companion to an additional Unified Requirement (UR S34) dealing with minimum loading conditions that should be analysed.
New S34 is applicable to container ships only and will apply from 1 July 2016 and requires a global (full ship) analysis for ships with length = 290 m and a cargo hold analysis for ships with length = 150 m.
IACS said it “firmly believes that proper casualty investigation and subsequent information sharing is a key element to achieving continuous improvement in safety standards”.
At the beginning of 2014, IACS established an expert group on structural safety of container ships to undertake a post “MOL Comfort” review of available information and also to examine a number of past casualties. This work has resulted in the creation of UR S11A, which is a longitudinal strength standard for container ships that explicitly addresses the three issues requested of both individual classification societies and IACS by the authors of the MLIT investigation report.
Bi-axial stresses that would be induced by lateral loading, i.e. external pressure on the bottom shell: IACS Members have for many years addressed these bi-axial stresses in their individual rules and procedures. The effect of the lateral loads that induce bi-axial stresses of bottom shell plates should be considered in the requirements of the hull girder ultimate strength and this will now be recognised in the new IACS Longitudinal Strength Standard for Container Ships, known as Unified Requirement S11A, which will enter into force on 1 July 2016.
The whipping effect on container ships: Although this phenomenon continues to be the subject of research, the effects are becoming better understood and some individual IACS Members have developed specific rule requirements in this regard. The development of an IACS Unified Requirements for the whipping component of hull girder loading will take time, however in the interim IACS has introduced a functional requirement into the new Unified Requirement S11A that requires IACS Members to take into account whipping in accordance with their individual procedures. Entry into force is again 1 July 2016.
A revised wave bending magnitude and longitudinal distribution has been included in the development of the new Unified Requirement S11A full details of which will be made available on the IACS website shortly.
UR S34 sets consistent requirements among IACS members by defining the unified minimum load cases used while performing strength assessment of container ships by Finite Element (FE) analysis. This fulfills two principal aims. Firstly, by prescribing high-level “functional requirements” on loads, the bottom line of structural strength becomes unified and, secondly, by developing a minimum set of common loading conditions for Cargo Hold Analysis in the midship region, a baseline for structural strength at cargo hold in the midship region is achieved.