ClassNK ships OCCS framework covering full CO2 value chain

ClassNK released a new handbook on October 23, 2026, that sets out a framework for implementing onboard carbon capture systems (OCCS) — and its central message is that capture equipment alone will not deliver verified emissions reductions for shipowners.

The publication, titled Onboard Carbon Capture Systems Implementation Framework, forms part of the Japanese classification society's Handbook on Ship GHG Emissions Evaluation series. It is aimed at shipowners, operators and other maritime stakeholders weighing investments in capture technology, and it structures project assessment across the entire CO2 management value chain rather than the vessel in isolation.

That framing matters commercially. An OCCS installation captures CO2 from ship exhaust gases, processes it and stores it temporarily aboard before transfer ashore. According to ClassNK, successful implementation also depends on shoreside infrastructure for unloading, transporting, storing or utilising that captured CO2, plus reliable mechanisms for measuring and verifying the claimed emissions reductions. A shipowner who buys capture hardware without a receiving terminal and a verification chain has, on the society's own reading, an incomplete project.

What does the handbook actually cover?

The document consolidates requirements in four areas:

• Onboard capture and storage arrangements
• Shoreside infrastructure for downstream CO2 handling
• Regulatory considerations
• Assessment of emissions-reduction performance

Two mechanisms receive particular attention. The first is Monitoring, Reporting and Verification (MRV), which underpins how emissions and emission reductions are measured and validated. The second is Chain of Custody (CoC), the tracking system that follows captured CO2 and its associated data through the supply chain after it leaves the vessel.

Both are the connective tissue between a physical capture operation and a bankable, certifiable emissions claim. Without MRV and CoC, there is no agreed answer to how captured carbon is handled post-transfer or how the resulting reductions are quantified — the two questions that will determine whether OCCS investments count toward regulatory or commercial decarbonisation targets.

How does it build on ClassNK's earlier work?

The handbook is not the society's first word on the subject. ClassNK previously issued Guidelines for Onboard CO2 Capture and Storage Systems, through which it developed safety and technical requirements for capture and storage arrangements while accumulating knowledge from demonstration projects and greenhouse gas certification activities.

The new publication takes a broader approach: rather than specifying equipment, it assembles the considerations involved in planning and evaluating an entire OCCS project. ClassNK said the document is intended to facilitate discussions among stakeholders and support the assessment of specific capture initiatives.

A caveat is warranted here. The handbook is guidance, not a mandated standard, and the source is silent on how many vessels currently operate OCCS installations or how much CO2 has actually been captured and verified under such arrangements. The framework addresses a value chain that, in much of the world, is still being built; the shoreside unloading and storage infrastructure the document treats as a prerequisite remains the least developed link.

Where can operators access it?

The Onboard Carbon Capture Systems Implementation Framework is available through ClassNK's Transition Support Services website and its MyPage technical publications platform.

The guidance arrives as shipping continues to explore multiple decarbonisation routes — energy-efficiency improvements, alternative fuels and exhaust-capture technologies — and ClassNK has stated it will keep supporting the sector with technical information and guidance as those options mature.