As the cruise industry advances towards lower-carbon propulsion, the maturing fleet of LNG-fuelled passenger vessels enters a new lifecycle phase. For the earliest adopters, this means navigating their first major renewal surveys and dry-docking campaigns with systems that are significantly more complex than those found on conventionally fuelled vessels.
The recent renewal surveys and dry-docks of Carnival UK’s (CUK) Iona and Carnival Cruise Line’s (CCL) Mardi Gras marked the first major LNG dry-docks for large passenger vessels in Europe. Pivotal to these achievements were the early, structured, and sustained involvement of LR’s Cruise Ship Centre of Expertise (CCoE). The CCoE orchestrated the technical alignment, planning discipline and global survey coordination required for such complex projects.
For LR, CUK and CCL, the work represented the execution of a highly sophisticated technical programme, the culmination of more than a year of detailed collaboration, planning and risk management. The lessons learned already shape thinking around future alternative-fuel ship designs and the evolving expectations of operators undertaking demanding maintenance schedules.
A new era of dry-docking
Dry-docking a LNG-fuelled cruise ship is a fundamentally different exercise from a conventional refit. With vessels spending only a brief period out of service, LNG system maintenance windows are correspondingly narrow.
As Remco van Ee, Senior Surveyor in Charge New Construction and MEC Rotterdam at LR, explains, “Cruise ships spend a relatively short time in drydock, 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.”
This compression of activity drove the need for unprecedented levels of forward planning. Spare part procurement alone demanded long-range forecasting, with lead times of up to 12 months for items such as LNG pumps. OEM specialist availability had to be locked-in early, and survey sequences aligned around delivery schedules and the operational constraints of the vessels themselves.
Andrew Bennett, Machinery Survey Policy Manager in LR’s Technical Directorate, explains. “Starting 18 months in advance, we worked closely with the client to understand their specific operation, maintenance and drydocking challenges, and helped them to develop detailed schedules, with optimised surveys agreed in advance and aligned to meet their requirements.”
This collaborative planning effort included shipboard visits, risk assessments, technical workshops and repeated sessions with Carnival’s technical teams in Miami, Southampton, Marseille and at the Carnival training centre. The aim was to build a shared and granular understanding of system conditions, survey requirements, and the operational profile of each vessel.
Vincenzo Prinzi, Technical Operation Director, CCL, reflects: “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, CUK, says: “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. Working closely together allowed us to address challenges quickly, maintain high safety standards and strengthen our capabilities in this emerging area.”
The inherent complexity of LNG fuel systems shaped every decision. Both Iona and Mardi Gras feature three fuel tanks and dual fuel trains designed for full redundancy, supported by sophisticated control logic and an extensive cryogenic piping network.
“Managing the inspection, testing and recommissioning of these systems within the confines of a passenger ship’s operational profile required not only expert knowledge but tight integration between the shipboard team, the technical office and the attending class surveyors,” says van Ee.
“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 demands
Each ship carried its own set of operational requirements and constraints that influenced the survey strategy.
For Iona, regular operations in the Norwegian fjords mean continuous LNG capability is essential to maintaining NOx Tier III compliance. Downtime for the LNG system therefore had to be minimised, placing even greater importance on the precision of the maintenance and recommissioning sequence.
For Mardi Gras, the transit from Cape Canaveral to Marseille exceeded the vessel’s Safe Return to Port (SRtP) radius, as discussed with the Bahamas Maritime Authority. This required one LNG fuel tank and propulsion line to remain fully operational throughout the crossing to extend the vessel’s viable range. Survey and inspection tasks had to be arranged around this operational constraint, which meant careful isolation planning and staged maintenance for uninterrupted system availability.
Surveys with passengers on board
One of the biggest operational challenges emerging from these projects is that many inspections cannot wait for dry-dock. LNG tank inspections and elements of fuel system testing had to take place while the vessels were in-service and carrying passengers.
These in-operation inspections required careful orchestration between ship staff, Carnival engineering teams and LR surveyors to avoid disruption while maintaining the highest safety standards. Isolation arrangements, venting plans and access procedures were codified in detail, to make sure every step had been risk-assessed and validated by all parties.
On Mardi Gras, inspections took place 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 that completed the renewal survey cycle.
“All inspections and surveys were completed safely, on time and to the satisfaction of all parties,” van Ee reflects, emphasising the support from LR survey teams in Miami, Marseille, Gdansk and Rotterdam as critical to achieving this outcome.
Influencing the future of LNG and alternative fuels
For Carnival, these renewal surveys represented not only a regulatory milestone but an opportunity to refine LNG maintenance strategies across its LNG-fuelled fleet. Working alongside LR brought greater predictability and structure to LNG overhaul activities allowed the owners to minimise operational disruption and embed stronger planning discipline in future dry-dock cycles.
“These first-generation LNG cruise ships have highly complex systems and requirements,” says Bennett. “Focusing collectively on their renewal surveys is providing lessons that will shape the future of alternative fuel system design, operation, maintenance and survey practice.”
As operators expand their LNG-powered fleets and begin adopting methanol, biofuels and future synthetic fuels, the procedural groundwork established here will serve as the foundation for a broader shift in how the industry approaches alternative-fuel ship maintenance. Inspections during passenger service, multi-location survey planning, long-lead spares preparation, and early-stage risk modelling are all likely to become the norm.
What comes next
The dry-docks of Iona and Mardi Gras represent a more collaborative, data-driven and anticipatory framework for alternative-fuel vessel assurance. The success of these projects shows what can be achieved when collaboration begins early and sustains through every stage of planning and execution.
Nick Playle, Refit Project Manager, CUK, says “This achievement was the result of an extensive joint effort to define an approach that satisfied both Lloyd’s Register and Carnival UK objectives—ensuring safe, reliable operations throughout the next survey cycle. 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.”
These projects also demonstrate the value of the Cruise Centre of Expertise model in bringing LR’s global expertise together early, for alignment and consistent delivery across regions and disciplines. As LNG cruise ships age and fleet numbers grow, these experiences offer a blueprint for the industry.