IACS CSR, DNV, ABS, LR, BV, NK: Classification Society Rules Explained

Classification societies set the structural standards that ships must meet to be built and insured. For anyone reviewing ship drawings, understanding these rule sets — and how they differ — is essential. This reference gives a plain-English overview of the major societies and what their rules require.

IACS Common Structural Rules (CSR)

The International Association of Classification Societies (IACS) publishes the Common Structural Rules, a harmonised set of requirements for bulk carriers and oil tankers. CSR standardises structural scantling requirements across member societies, so a design meeting CSR meets a common baseline regardless of which society ultimately classes the vessel.

The major individual societies

• DNV (Det Norske Veritas) — one of the largest classification societies, with comprehensive structural rules widely used in Europe and beyond.
• ABS (American Bureau of Shipping) — the principal U.S. classification society, with its own detailed structural requirements.
• Lloyd’s Register (LR) — a long-established British society with a full structural rule set.
• Bureau Veritas (BV) — a French society whose rules and tools (such as MARS) are widely used in structural verification.
• Nippon Kaiji Kyokai (NK / ClassNK) — the major Japanese society, prominent across Asian shipbuilding.

What compliance requires

Whichever society applies, structural compliance comes down to demonstrating that each member meets or exceeds the minimum scantling the rules require. That means calculating properties such as plate thickness and section modulus, comparing them against the rule minimum, and documenting the margin with the relevant clause reference.

The challenge is that each society expresses its requirements differently, and a design may need to be checked against more than one rule set. Doing this manually for every member on every drawing is slow and error-prone.

Automating multi-class compliance

ShipWright AI supports all of these rule sets — IACS CSR, DNV, ABS, Lloyd’s Register, Bureau Veritas, and NK — in a single platform. It runs real scantling calculations using the actual rule formulas, produces PASS/FAIL margins for every member, and generates structured PDF reports with clause references. Instead of switching between separate single-society tools, a naval architect can verify a drawing against the applicable rules in one place. Try it free to see multi-class compliance in action.