An Introduction to Vessel Classes

Classification societies play a fundamental role in today’s marine industries with the vast majority of commercial ships built to standard. A society will act on behalf of ship owners and builders to ensure high build quality and the safety of a ship’s main structural parts. Classification also provides a point of reference with regard to those who were involved in the supply chain including builders, charterers and insurers.

The process begins at the design phase, focussing heavily on the implementation and manufacture of key components and technical specifications. The standards which must be adhered to are dictated by the regulations of the chosen society and are published as rules, evolving continuously to incorporate emerging market technology and client demand via the advice of highly competent engineers and architects.

All classification societies waive liability for future faults as a surveyor can only record a vessel’s quality at the time of inspection; it is then the responsibility of the ship owner to maintain the vessel and inform the society in the event of damage or structural alteration. Although the surveys are thorough, they do not cover all aspects of a ship’s build and operating service. This can include crew qualifications, navigational aids and manoeuvrability.

There are currently 13 members of the International Association of Classification Societies (IACS), each with a unique set of rules, classification layouts and notations. Five of the biggest classification societies are listed below, along with their identifying signature:

The codes following the society’s standard signature are not interchangeable between organisations, meaning each letter or number will represent a different characteristic for each society. In addition, notations will often need to be checked to ensure they refer to the correct vessel, chapter and section, ranging from High Speed Light Crafts to Passenger Ship. Each code can be broken down to highlight a ship’s capabilities, equipment or restrictions.

For example:

DNV GL 1A1= Society, construction symbol and main character of class (assigned to all vessels)

SF= Compliance with damage stability requirements

DYNOS-AUTR = Dynamic Positioning with a redundant DPS and an independent joystick system back-up

RP = Redundant Propulsion

E0= Instrumentation and automation installed to allow for unattended machinery space

HELDK-SH = Helicopter landing area or erected platform covering basic strength requirements and additional requirements to ships safety

W1 = Integrated navigational system

SBM= Management of safety and environment protection in ship operation

Complex characteristics are categorized in varying ways, featuring below are vessels with Dynamic Positioning (DP) Systems and those operating under Restricted Service.

DP-capable vessels are categorized differently by each organisation but adhere to the main equipment classes as set out by the International Maritime Organisation (IMO). See below for society examples:

Service area restrictions are also listed within classifications, again differing between societies. ABS prefers to write restrictions within text seated in the code, for example:

However many will team a notation with a restriction in Nautical Miles (NM):

Due to a growing demand for Installation Vessels (IV), many of the largest classification societies are directing their focus at forming notations for specialised maintenance, repair and installation units. The widening of a ship’s capabilities has meant many societies are now compiling reformed sets of rules to fall in line with developing technical issues and hazards.

With DNV being one of the first societies to recognise the importance of IV Classification, class notations will become an increasingly important part of a commercial vessel’s specification, and ultimately, desirability.

Crew Transfer Vessels

Smaller vessels are categorised differently, adhering to different requirements and statutory regulations. With a heavier focus on passenger numbers and distance of operation from shore, the Maritime and Coastguard Agency (MCA) outlines guidance for UK vessels (up to 24 metres in length) which are used for charter or commercial use.

Crew Transfer Vessels are playing a progressively crucial role in the operation and maintenance of offshore wind farms, transferring thousands of technicians to various locations around the world.