- Keywords: Technical, Maritime
Relevant for design offices, shipyards, owners/managers of bulk carriers and oil tankers.
The most important changes of the modified CSR are as follows:
- The IMO has considered the assumptions in the CSR on how vessels are operated in heavy weather as not sufficient. The consequence of this is increased hull girder vertical wave bending moment, shear force and external sea pressure by 5% for yielding and ultimate strength check. The loads related to the fatigue requirements have not been increased.
- The IMO has considered the assumptions in the CSR on how much time smaller bulk carriers are operated in heavy ballast condition as not sufficient. The consequence for fatigue capacity evaluation is to increase the time in heavy ballast condition from 15% to 25% for bulk carriers (BC-B and BC-C) with a length less than 200 m.
- The IMO has considered the assumptions in the CSR on the effectiveness of the corrosion protection systems as not sufficient. For fatigue calculations, the time in a corrosive environment shall be increased:
- From 5 years to 10 years for water ballast tanks, oil cargo tanks and lower parts of bulk cargo holds and water ballast cargo holds
- From 2 years to 5 years for bulk cargo holds and water ballast cargo holds, except lower parts
The application of these changes to existing ship designs may influence steel weight and certain design details. The magnitude of these changes depends on the size of vessel, type of stiffener profiles used and the degree of optimization of the existing designs.In general, the following changes can be experienced in the parallel mid-ship area:
- The required hull girder sectional modulus is increased by about 1% to 3% due to the increased vertical wave bending moment. The scantling consequence depends on the sectional modulus margin of existing design.
- Typically, a 3 years’ reduction in fatigue life may be expected due to increased dynamic load and increased time in a corrosive environment. Fatigue critical details may need to be improved or the scantlings may need to be increased to reduce the dynamic stress range by approx. 5%.
- For limited areas in the bottom, plate thickness may need to be increased by 0.5 mm due to the local plate requirements.
- Required sectional modulus for longitudinal stiffeners on the inner bottom is increased by about 2% to 3% to meet the local stiffener requirement.
- Longitudinal stiffeners in way of deck and upper part of longitudinal bulkheads may need to be increased to satisfy stiffener buckling requirements.
It is worth noting that minimal impact is expected for vessels with DNV GL fatigue class notations, e.g. CSA or PLUS. This is because these class notations already contain provisions on increased global strength and detailed fatigue check for deck attachments.
In summary, the rule changes in the January 2017 CSR rule version may require some strengthening of existing ship designs. The actual change in steel weight is expected to be limited due to some margin on the existing scantlings.
The modified CSR rules are applicable for bulk carriers (L ≥ 90m) and oil tankers (L ≥ 150m) contracted for construction on or after 1 July 2017. Owners and builders need to know which rule version applies for their vessels:
- In case a new contract is signed on 1 July 2017 or later, the January 2017 version applies.
- In case of a contract signed before 1 July 2017, the previous rule version applies if not otherwise agreed.
- The previous rule version will also apply to options covered by contracts signed before 1 July 2017 and which are declared within 12 months from contract date.
CSR Rule at IACS website at: iacs.org.uk/publications/common-structural-rules
For customers only: DATE – Direct Access to Technical Experts via My DNV GL
Otherwise: Use our office locator to find the nearest DNV GL maritime office or email us
2020 Sulphur update - outcome of the MEPC 74
The 74th session of the Marine Environment Protection Committee (MEPC 74) was held at IMO in London on 13–17 May 2019. This was the last MEPC meeting before the 0.50% global sulphur limit takes effect on 1 January 2020, and the focus was on the implementation and completion of guidelines to help stakeholders prepare and ensure consistent implementation. We strongly recommend stakeholders to prepare in due course and update plans according to the latest IMO guidance. This statutory news contains a summary of sulphur-related resolutions and circulars adopted at MEPC 74.
EU MRV and IMO DCS - some practical recommendations
This technical news contains some recommendations relevant to both EU MRV and IMO DCS.
Prepare for the Global Sulphur Cap 2020 with the IMO Ship Implementation Plan
The IMO has agreed on 1 January 2020 as the date for switching to 0.50% sulphur fuel globally. Now, as ship owners face the daunting task of preparing for the fuel oil switch, proper planning is essential. The IMO Guidance for developing a Ship Implementation Plan (SIP) is a useful tool, and described further in this technical news.
Survey by remote inspection techniques - use of approved service suppliers
The use of remote inspection techniques (RIT) is increasing. Today, drones, climbers, or robot arms, can be used as an alternative to close-up surveys in both the DNV GL rules and IACS Unified Requirements. RIT may significantly reduce the survey time and costs, while improving the safety of surveyors and the owner’s personnel. From 1 January 2019, DNV GL has approved the use of service suppliers for RIT. This technical news explains how RIT can be used and how suppliers can achieve DNV GL approval.