Lloyd's Register (LR) has completed what it describes as Europe's first major dry docks for LNG-fuelled large passenger vessels, working with Carnival UK and Carnival Cruise Line on renewal surveys for the Iona and Mardi Gras.

The projects, which concluded in 2025, involved more than 18 months of advance planning and required inspections to be carried out while passengers remained on board — a departure from conventional dry dock procedures.

According to LR, the work demonstrates the increased complexity of maintaining LNG-fuelled cruise ships compared to conventionally fuelled vessels, with implications for how the industry approaches alternative-fuel vessel maintenance.

Extended planning windows

Andrew Bennett, Machinery Survey Policy Manager in LR's Technical Directorate, said: "Starting 18 months in advance, we worked closely with the client to understand their specific operation, maintenance and dry-docking challenges, and helped them to develop detailed schedules, with optimised surveys agreed in advance and aligned to meet their requirements."

The planning process included shipboard visits, risk assessments, technical workshops and sessions with Carnival's technical teams in Miami, Southampton, Marseille and at the Carnival training centre.

Spare part procurement required lead times of up to 12 months for components such as LNG pumps, according to LR. Original equipment manufacturer specialist availability had to be secured early, with survey sequences aligned around delivery schedules and operational constraints.

Compressed maintenance windows

Remco van Ee, Senior Surveyor in Charge New Construction and MEC Rotterdam at LR, explained: "Cruise ships spend a relatively short time in dry dock, limiting the time we have for the maintenance of the LNG system. Halfway through each dry dock, we needed to start preparing the LNG installation for taking on its first bunkering directly after the docking period."

Both vessels feature three fuel tanks and dual fuel trains designed for redundancy, supported by control logic and cryogenic piping networks. Van Ee noted: "We had to define a very detailed Inspection and Test Plan for these vessels, down to the smallest valve which required overhaul well in advance of the actual surveys."

Vessel-specific constraints

Each ship presented distinct operational requirements that influenced survey strategy.

For Iona, which operates regularly in Norwegian fjords, continuous LNG capability is required to maintain NOx Tier III compliance. This necessitated minimising downtime for the LNG system during maintenance.

For Mardi Gras, the transit from Cape Canaveral to Marseille exceeded the vessel's Safe Return to Port radius, as discussed with the Bahamas Maritime Authority. One LNG fuel tank and propulsion line had to remain operational throughout the crossing, requiring careful isolation planning and staged maintenance.

In-service inspections

LNG tank inspections and elements of fuel system testing took place while vessels were in service and carrying passengers, according to LR.

On Mardi Gras, inspections occurred during transatlantic sailing, in dry dock, and during the subsequent voyage from Barcelona. For Iona, the sequence spanned a voyage from Southampton, the Rotterdam dry dock, and a final commissioning voyage.

Van Ee stated: "All inspections and surveys were completed safely, on time and to the satisfaction of all parties."

Industry implications

Vincenzo Prinzi, Technical Operation Director at Carnival Cruise Line, commented: "The preparation for this project was extensive, and it allowed us to engage in meaningful discussions and work together with determination. Our strong communication played a key role in reaching a consensus on everything we planned."

John Waters, LNG Inspection Project Manager at Carnival UK, said: "The recent inspection of the LNG fuel system on Iona marked a first for Carnival UK and the collaboration with LR was important in its success. The communication and constructive approach helped navigate this new ground with confidence."

Bennett noted: "These first-generation LNG cruise ships have highly complex systems and requirements. Focusing collectively on their renewal surveys is providing lessons that will shape the future of alternative fuel system design, operation, maintenance and survey practice."

Nick Playle, Refit Project Manager at Carnival UK, added: "The ultimate goal is to leverage the insights gained, embed lessons learned, and formalise best practices into future standards for adoption across all vessels with similar systems."

LR says the procedural framework established through these projects — including inspections during passenger service, multi-location survey planning, long-lead spares preparation, and early-stage risk modelling — is likely to become standard practice as operators expand LNG-powered fleets and adopt methanol, biofuels and synthetic fuels.