ClassNK Publishes Implementation Framework for Onboard Carbon Capture

Classification society ClassNK has released a new handbook, Onboard Carbon Capture Systems Implementation Framework, as the latest volume in its Handbook on Ship GHG Emissions Evaluation series. The document is aimed at shipowners, operators and maritime stakeholders weighing onboard carbon capture systems (OCCS) as a route to fleet decarbonization.

The timing is commercial, not academic. As the shipping sector weighs operational measures, energy-efficiency hardware and alternative fuels against decarbonization targets, onboard capture from vessel exhaust gases has positioned itself as a potential bridge solution for commercial fleets. ClassNK's framework arrives before capital commitments, not after them.

What does the handbook actually cover?

The guidance spans the full project lifecycle rather than the shipboard hardware alone. Its scope includes:

• Shipboard capture technology and technical feasibility evaluation
• Offloading logistics from vessel to shore
• End-use or sequestration pathways for captured CO2
• Monitoring, Reporting and Verification (MRV) protocols
• Chain of Custody (CoC) traceability mechanisms

The framework draws on ClassNK's existing Guidelines for Onboard CO2 Capture and Storage Systems, on technical demonstration projects, and on the society's greenhouse gas certification services. In effect, it consolidates technical, regulatory, infrastructure and emissions accounting perspectives into a single project framework.

The takeaway: a shipowner can now evaluate an OCCS project end to end from one document, rather than assembling the picture from scattered sources.

Why does verification matter more than hardware?

ClassNK's central argument is that installing capture equipment proves nothing. Verifying real-world greenhouse gas reductions from OCCS extends beyond retrofitting or installing onboard capture hardware, the society stresses.

Credible decarbonization claims, in its view, rest on two accounting mechanisms. The first is MRV: standardized protocols to quantify actual CO2 volumes captured and stored onboard during voyage operations. The second is Chain of Custody: traceability frameworks that track captured CO2 and its associated carbon attribute data from vessel discharge through final offload, transport, and permanent geological sequestration or industrial utilization.

That second leg carries the commercial weight. Without traceability from discharge point to final storage or use, a captured tonne of CO2 is an unverified claim with no market value.

The takeaway: the capture unit is the easy part; the paperwork that follows the molecule decides whether the tonne counts.

What infrastructure has to exist first?

ClassNK is explicit that commercial adoption does not hinge on ships alone. Successful deployment depends on establishing reliable offloading, transportation and port receiving infrastructure, alongside permanent subsea storage or industrial utilization pathways for the captured gas.

This places OCCS in the same dependency chain as other downstream carbon streams: without port-side receiving capacity and verified sequestration or utilization outlets, onboard capture has nowhere to send its product. The framework treats those pathways as project preconditions rather than later-stage details.

The takeaway: a capture-ready fleet is worthless without a discharge-ready coast.

What happens next?

ClassNK has framed its framework as a pre-investment tool, giving stakeholders a unified basis for evaluation ahead of capital commitments. The development sits alongside parallel moves in the field: DNV has launched a standardized framework for onboard carbon capture, and onboard capture via mineralization has drawn attention from EU ETS and IMO quarters.

The milestone to watch is the first commercial OCCS project that closes the full loop — capture, offload, transport, and verified sequestration — under an audited chain of custody. Until one does, the framework remains guidance, and the tonnage remains theoretical.