Rules for classification of ships - July 2021 edition

The 2021 July edition of the DNV rules is now available.

General information

The July 2021 edition of the rules and offshore standards were formally approved 18th of June 2021 by Group CEO Remi Eriksen and are now available.

The main highlights in this edition are:

  1. New class notations, such as operational reliability – OR, ammonia as fuel – Gas fuelled ammonia, nautical safety – NAVI, and ship type notation – Deck carrier.
  2. Updated requirements to main class, ship type notations, additional class notations and survey requirements.
  3. Implementation of external requirements, such as IACS unified requirements and IMO regulations.

The entry into force date for the rules is 1st of January 2022. The rules may, however, be applied to projects contracted before this date upon agreement between parties.

For more information on the changes, please contact your local DNV office.

In addition to the changes in the rules for ships, some changes have also been made to rules for:

  • Naval vessels
    • continuing the introduction of a new rule regime adding on requirements for “Materials and welding” and “Fleet in service”.
  • High speed and light crafts.
  • Inland navigation vessels.
  • Floating docks.
  • Underwater technology.

Rules for classification of offshore units and offshore standards will be presented separately.

Overview of the main changes in the rules for classification of ships

Main class

TopicRule reference DNV-RU-SHIPMain topcis
General regulationsPt.1 Ch.1
  • responsibility for system integration
  • repair of equipment at newbuilding
Materials and welding
Metallic materials
Pt.2 Ch.2
  • additively manufactured products
  • special metallic materials
Materials and welding 
Fabrication and testing
Pt.2 Ch.4
  • welder certificates
  • deep penetration fillet welds
  • ship construction file
Pt.3 Ch.4
  • design pressure for deck house sides
Local scantling
Pt.3 Ch.6
  • minimum thickness
Pt.3 Ch.8
  • slenderness requirements
Pt.3 Ch.9
  • bottom plating container ships
Special requirements
Pt.3 Ch.10
  • stem plate extent
Hull equipment, supporting structure and appendages
Pt.3 Ch.11
  • equipment number - anchoring equipment
  • ship design mooring load
System and components
Rotating machinery – driven units
Pt.4 Ch.5
  • propellers advanced calculations
System and components
Piping systems
Pt.4 Ch.6
  • alignment with external requirements
  • air lubrication systems included
Fleet in service
Survey requirements
Pt.7 Ch.1
  • survey of watertight cable transits
  • survey of towing winch emergency release systems
  • hull survey plan for renewal and intermediate surveys based on the actual operation and historical condition of the ship and similar ships

Ship type notations

Class notationRule reference DNV-RU-SHIPMain topics
Container shipsPt.5 Ch.2
  • cell guides certification
  • membrane tanks for gas fuel
  • mixed stowage of containers - loading conditions
  • hatch coaming plates – edge grinding
Liquefied gas tankersPt.5 Ch.7
  • IACS/IMO updates
  • extending cargo list
  • alternative fuel
Deck carrierPt.5 CH.10 Sec.17
  • introducing new notation
    Deck Carrier

Additional class notations

Class notationRule reference DNV-RU-SHIPMain topics
Fuel cell installationsPt.6 Ch.2 Sec.3
  • technology update
  • fuel cell space concepts
Low flashpoint liquid fuelled enginesPt.6 Ch.2 Sec.6
  • IMO alignment
Alternative fuelsPt.6 Ch.2 Sec.8
  • introducing notation Fuel ready
Gas fuelled ammoniaPt.6 Ch.2 Sec.14
  • introducing new notation covering ammonia as fuel – 
    Gas fuelled ammonia
Operational reliabilityPt.6 Ch.2 Sec.15
  • introducing class notation for passenger vessels enhance reliability - OR
Dynamic positioning systemsPt.6 Ch.3
  • technology update
Nautical safetyPt.6 Ch.3 Sec.6
  • introducing notation NAVI
Regasification plantPt.6 Ch.4 Sec.7
  • restructuring notation REGAS
Prepared for new products - Gas carriersPt.6 Ch.4 Sec.15
  • introducing new notation
    Ready for C
Cold climatePt.6 Ch.6 Sec.1
  • restructured the rules to present all general
Underwater noise emissionsPt.6 Ch.7 Sec.6
  • adapted Silent notation to better suit non-passenger vessels
External airborne noise emissionsPt.6 Ch.7 Sec.8
  • redesigned Quiet notation to also include prescriptive noise level requirements and introduced vessel rating system

Highlights from main changes

General regulations (Pt. 1)

  • Clarified that the responsibility for system integration onboard a newbuilding lies with the ship builder.
  • Clarified that the Society may accept repaired, but new equipment onboard newbuilds when operational life time and/or maintenance schemes are not adversely affected.

Materials and welding (Pt. 2)

  • Metallic materials (Ch. 2)
    • New section added for requirements and testing of additively manufactured products.
    • New section added introducing procedural requirements for special metallic materials.
    • New requirements for cold formed welded hollow sections.

  • Fabrication and testing (Ch. 4)
    • Requirements for revalidation of welder certificates aligned with IACS UR W32 -Qualification scheme for welders of hull structural steels.
    • Added requirements for how to perform deep penetration fillet welding and reduced the fillet weld throat thickness requirement.
    • Aligned the requirement for multi-pass increased thoughness welds with IACS requirements.
    • Introduced the requirement for the ship construction file to include watertight cable transits in line with IACS.

Hull (Pt. 3)

  • Loads (Ch. 4)
    • The pressure at deckhouse sides may be reduced in some areas for ships with high freeboard – such as LNG carriers or container vessels.
  • Local scantlings (Ch.6)
    • Minimum thickness requirements have been adjusted for superstructure side, watertight bulkhead, primary support members in peak tanks, sea chest boundaries and deck house end walls. The changes may give scantling reductions for some ships and for affected members without affecting safety.
  • Buckling (Ch. 8)
    • Non-linear finite element analyses have demonstrated that the slenderness factor was too conservative for stiffeners having marginal axial stresses. The rule changes give scantling reductions for flat bar stiffeners for some ships and typically on watertight floors and web frames.
    • The required flange breadth for L and T profiles is reduced by 20% in line with proposed IACS CSR.
  • Fatigue (Ch. 9)
    • Changed the level B requirements for the bottom plating of container ships to lower level C based on global strength model fatigue results of container ships of different sizes. Should influence positively on the construction time.
  • Special requirements (Ch. 10)
    • The requirement to the vertical extent of stem plates is limited from lower waterline and up to 0.6 m above deepest waterline. The requirement to transverse extent of stem plating is removed.

Systems and components (Pt. 4)

  • Rotating machinery – driven units (Ch. 5)
    • Accepting reduced safety factors for propellers when strength assessment is based on advanced, more reliable calculations (computational fluid dynamic / finite element calculations).

Ship types (Pt. 5)

  • Container ships (Ch. 2)
    • Reduction in requirement for compliance document type for cell guides. Now accepting a material declaration issued by the manufacturer.
    • Introduced rules for membrane tanks in loading case tables.
    • Removed the container mixed stowage loading case from the FEA loading conditions, facilitating reduced steel weight for hatch cover supporting structures.
    • Modified requirements for hatch coaming plates – removed requirement for rounding including the specified radius.
  • Liquefied gas tankers (Ch. 7)
    • Extending the cargo list to also include fuel types other than methane; typically propane and ammonia.
    • Introducing requirements for carrying hydrogen as cargo.
  • Vessels for special operations (Ch. 10)
    • New class notation Deck carrier meeting market need in relation to e.g. floating wind park installations.

Additional class notations (Pt. 6)

  • Propulsion, power generation and auxiliary systems (Ch. 2)
    • New class notation Fuel ready enabling market to prepare the various parts of a complete fuel system for later conversion to alternative fuels.
    • New class notation Gas fulled ammonia facilitating the use of ammonia as fuel. Covering installations from the ship’s gas fuel bunkering connection up to and including the consumers.
    • Introducing a new class notation on operational reliability – OR – for passenger vessels. The notation is building on the safe return to port concept and offers three qualifiers related to 1) reliability of propulsion, steering and electrical power 2) reliability of manoeuvring and 3) operational reliability during damage and maintenance scenarios.
  • Navigation, manoeuvring and position keeping (Ch. 3)
    • Introducing a new class notation NAVI providing requirements in accordance with SOLAS V/15 recommendations, relating to bridge design and arrangement of navigational equipment.
  • Cargo operations (Ch. 4)
    • Restructured the content of the class notation REGAS to meet market expectations on relevant safety requirements and removed present qualifier ES accordingly.
    • Offering a new class notation Ready for C facilitating market need (gas carriers) to communicate being prepared for carrying new/other products.

Information in relation to company name change

As of March 1st, 2021, DNV rebranded from DNV GL. As a result of this, the Society will operate with rules published under the brand names DNV and DNV GL in a transition period.
The rules valid for a specific project and/or vessel/unit, is decided by the date of 'contract for construction'.
Also in a transition period, rules published under the brand name DNV will include references to rules and supporting documents published under the brand name DNV GL.

Information on coming rule editions

DNV publishes one main rule edition annually. The next main rule edition will be published in July 2022.
Additional amendments may be carried out, and all amendments will be specifically marked in the rules table of contents found here.

Oslo, Norway, 2021-06-28
Henning B. Karlsen
Service Responsible – Ship Class


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