Circularity Assessment of Vessel Refits

Abstract

The global maritime sector faces increasing pressure to reduce greenhouse gas emissions, comply with emerging regulatory frameworks, and transition toward more resource-efficient fleet renewal strategies. While vessel refits are frequently promoted as circular alternatives to newbuild vessels, decision-makers lack systematic tools to evaluate the strategic, environmental, and economic impacts of different refit pathways. Existing circular economy assessment frameworks are either too generic, developed for land-based industries, or primarily focused on newbuild vessels. This thesis addresses this gap by developing a structured, KPI-based methodology that supports early-stage decision-making for vessel refits, enabling transparent comparison between repair, refurbish, remanufacture, and newbuild alternatives.

A Design Science Research approach is applied to derive a two-step framework. The first step identifies feasible circular strategies based on vessel and component characteristics, regulatory requirements, and intervention depth. The second step evaluates each strategy using 32 Key Performance Indicators (KPIs), synthesised from an initial database of 87 indicators derived from literature, regulatory documents, and industry sources. The final KPI set spans three impact areas, strategic, environmental, and economic, and is organised across seven themes: design and modularity, material circularity, cost and economic viability, lead times and availability, quality and performance, environmental impact reduction, and regulation and standardisation. System boundaries align with maritime assessment practices, applying cradle-to-gate for capital emissions, tank-to-wake for operational emissions, and excluding maintenance, transport, and end-of-life phases where data is insufficient or inconsistent.

The framework is demonstrated using a case study on a 20-year-old Damen ASD 3110 tug. Three refit strategies, refurbish (conventional diesel), remanufacture to hybrid propulsion, and remanufacture to full electric, are compared with representative newbuild vessels of equivalent concepts. Results show that all refit strategies significantly reduce project lead time (10–14 months vs. ~24 months), capital expenditures, and hull-related embodied emissions (saving 535–633 tonnes of CO₂ compared to newbuilds). Environmental performance diverges by propulsion type: refurbishing yields the lowest capital emissions but highest operational emissions, whereas electric remanufacture achieves zero operational emissions but the highest total cost of ownership. Hybrid remanufacture offers a balanced profile, reducing operational emissions by approximately 40% while maintaining economic competitiveness with refurbish strategies over a 20-year horizon. Sensitivity analyses indicate that relative performance depends strongly on energy prices, vessel lifetime assumptions, and regulatory context.

The study concludes that refits can serve as robust, circular alternatives to newbuilds for workboat-type vessels, provided that intervention scope, component availability, and operational profiles are appropriately matched. The proposed framework enables consistent evaluation of trade-offs and supports alignment with the EU Taxonomy and sustainable financing mechanisms. Recommendations include expanding environmental boundaries to well-to-wake analysis, improving data availability through digital product passports, refining economic KPIs, and validating the methodology across additional vessel types and shipyards.