Design Standards

Design Standards

See the article on the Outcome of SDC 4 (4th session of the IMO Sub-Committee on Ship Design and Construction), 13-17 Feb 2017, at the link here.

During INTERCARGO's 35th Technical Committee meeting (London, October 2016), Peter Contraros delivered a comprehensive presentation on the IMO Goal Based Standards with an emphasis in the IMO Audit findings.

A copy of the presentation can be found on the TechComm page (member login required)

INTERCARGO performed a review of the second Rule Change Proposal (RCP 2) and accompanying Technical Background and  informed IACS, by letter,  of the comments and concerns.A copy of the letter can be found here (member login required)

In summary INTERCARGO is very concerned with the downgrading of welding requirements at critical locations with what appears to be no technical justification:

  • Hopper Sloping Plate to Inner Bottom Plate – Downgrade from full or partial penetration to partial penetration only.
  • Transverse Web Frame to Hopper Sloping Plate – Downgrade from partial penetration welding to fillet welding only.
  • Transverse Bulkhead (TB) Lower Stool Top Plate to TB Lower Stool Side Plate – Downgrade from full penetration welding  to partial penetration welding.

INTERCARGO expressed  concern that,  in addition to the decrease of strength/increase of stress that will be a result of the downgrades, the lack of full penetration welding will also affect the ability to fully assess the weld quality. Additionally, the lack of prescriptive requirements, within the Common Structural Rules (CSR), for enhanced inspections of the critical locations at new build will worsen the situation resulting in the welds at these locations not lasting the CSR design life.

INTERCARGO also expressed their disappointment that the Rule Change Proposal did not align the various Class Societies’ NDE requirements (i.e. number of checkpoints) rather than leaving it to the discretion of the individual Class Society, which we believe is not in the spirit of the Common Structural Rules or SOLAS

INTERCARGO performed a review of IACS Draft Rule Change Proposal RCP 1 and provided the IACS Secretariat with a number of comments.  The letter, containing INTERCARGO's comments and concerns can be found here (member login required). A summary of the comments are as follows:

Part 1, Chapter 2, Section 4, 2.1.1 – Means of Access

INTERCARGO requests that  a cross reference to SOLAS Ch. XII Reg. 6-2.2, which stipulates minimum clear passage dimensions for access in double skinned bulk carriers, to be added.

Part 1, Chapter 3, Section 3  - 1.2.1 – Corrosion Addition Determination – Table 1

The RCP allows  for a  downgrade of corrosion allowance on the lower part of; plane bulkheads or bulkheads fitted without a stool. INTERCARGO questions the technical justification of this rule change.

Part 1, Chapter 3, Section 6  - 4.3.4 – Arm length (Tripping Brackets) & 10.4.10 – Upper stool

INTERCARGO asks for removal of  the non-technical term “general”  which the RCP adds to the existing rules.

Part 1, Chapter 7, Section 3 - 2.1.1 – List of Structural Details

INTERCARGO questions why fine mesh analysis is still  not mandatory for the fore and aft region of the vessel.

Part 1, Chapter 9, Section 6 - Table 5 – Design Standard E

The RCP allows for the downgrading of welding requirements at the connection the inner bottom to side girder in way of the hopper knuckle. INTERCARGO requests that the existing requirements are kept and states that an upgrade of the welding in this area is justified for this critical joint.

Part 1, Chapter 12, Section 3  - 4.2.4 – Slot Welds on Hatch Covers

The RCP removes the requirements for the size and spacing of slot welds on hatch covers, leaving the requirements for this detail up to the individual Class Society, INTERCARGO does not believe that that this is in the spirit of the Common Structural Rules or of the IMO Goal Based Standards.

Liquefaction is a phenomenon in which a soil-like material is abruptly transformed from a solid dry state to an almost fluid state. Many common bulk cargoes, such as iron ore fines, nickel ore and various mineral concentrates, are examples of materials that may liquefy.


If liquefaction occurs on board a vessel, the stability will be reduced due to the free surface effect and cargo shift, possibly resulting in capsizing of the vessel. The ship structure may also be damaged due to increased cargo pressures.


DNV GL has written a guideline for the design and operation of vessels with bulk cargoes that may liquefy. The intention of this guideline is to raise the awareness of the risks of cargo liquefaction on ships and to describe what mitigating actions may be taken to reduce such risks. The target group is ship designers, yards, shipowners and other stakeholders in the shipping industry.

 

Refer to the enclosed publications, with appreciations to DNV GL:

  • Bulk Carrier Update Article Cargo Liquefaction
  • Bulk Cargo Liquefaction Guideline for design and operation

The publications can also be downloaded from DNV GL webpage click here.