A 9,500-passenger(plus 2,200 crew) cruise ship destined for Asian markets pushes the design and construction limits of Safe Return to Port rules, requiring special simulation models to cope with complexities

When the first of Hong Kong-based Genting’s two giant Global-class cruise ships hits the water from the MV Werften Wismar yard in early 2021, it will make a ‘splash’ for the obvious reasons. At 208,000 gt and 342 m long, the 21-deck flagship for Dream Cruises sets new standards in size and will be the biggest cruise ship ever built in Germany.

But the sheer size of Global Dream will also create records for complexity, including for Safe Return to Port (SRtP) where it embodies the latest thinking. The 10-year-old regulation, based on the concept that ‘the ship is its best lifeboat’, had to be pushed to the limit for the Global class. “Based on the pure dimensions of the Global-class ships, there are about 1,200 casualty thresholds to be considered,” Hamburg-based consultancy Global Maritime’s Erik Werner told Passenger Ship Technology. “The assessments for SRtP were always going to be a challenge when we were contracted to do the work.”

Capable of carrying up to 9,500 passengers(plus 2,200 crew) in the peak holiday season, these vessels certainly ask a lot in terms of SRtP. For comparison, the consultancy calculates that a 130-m long, 11-deck cruise ship carrying 200 passengers requires 172 damage scenarios – effectively, danger points when something goes wrong – while a 230-m long, 15-deck ropax ferry with 1,800 passengers throws up 151 damage scenarios. But the numbers go exponential with a Global-class ship with its 21 decks, presenting no less than 1,205 damage scenarios. And since there are typically 16 SRtP ’essential groups’ – fundamentally vital shipwide systems – to be considered in SRtP calculations such as power and propulsion, they involve a swath of sub-systems – up to 53 by the consultancy’s assessment. On a Global-class vessel, the interrelated complexities are off the scale, with practically everything being linked in one way or another in the event of a catastrophic failure.

As SRtP becomes increasingly embedded in the design of passenger vessels, consultants such as Global Maritime are under siege from shipbuilders – and not just for cruise ships. “In recent years a lot of new shipyards with little experience in passenger ships have entered this attractive market, mainly from China but also smaller shipyards from Europe focusing on the expedition cruise sector. The interest is not just coming from yards wanting to minimise their risks but also from classification societies,” explains Mr Werner, an MSc in marine engineering and power plants with 20 years of experience in shipyards, classification societies and maritime consultancies. He is currently head of Global Maritime’s SRtP work and associated services.

The regulations, which apply to ships over 120 m long, set a high importance on redundancy, for instance of cables, bilge pumps, propulsion and communication, to name a few, so that key operations are maintained. The ship is assumed to be able to limp back to port under its own steam at about six knots. The vessel’s area of operation must also be taken into account – for instance, an expedition cruise ship may require extra redundancies because it could be far from the nearest port.

The work on the Global class required the consultant to raise its game to another level. Instead of the standard paper- based methods such as ’failure mode and effect analysis’ that are typically used for SRtP calculations for the offshore industry in, for example, dynamic positioning, the consultancy uses a ’functional simulation model’ that allows for much more accurate verification online as well as accommodating thousands of essential compliance checks.

“Our computational solution deals with the many casualty scenarios that are required by the regulations and calculates the required manual actions efficiently,” Mr Werner says. “Accurate action information, on a per casualty basis, allows drills to be conducted and ensures a rapid crew response.” The main advantage of the functional simulation model is its ability to process new developments as they emerge, allowing everything to be updated and recalculated throughout the entire process. Mr Werner says “[It starts with] the early design verification and runs right through to the as-built approval. When you do not have to update documentation manually, changes can be easily tested, verified and included into approval documentation on a regular basis. This greatly speeds up the overall approval process.”

There are extra benefits in terms of after-the-fact checks. “The model acts as its own auditable record of the assessment process,” adds Mr Werner. “The authorities can use this to ensure that the high-level principles are correct and that the design, in detail, matches the as-built vessel.”
Global Maritime’s work on the big ships has greatly expanded the consultancy’s intellectual property in SRtP. “We are using our methods for all our current and future SRtP projects,” he says. “We are permanently improving them with a special focus on software handling and calculation time, database integration with our clients and automatic reporting functionalities. The integration of the database and the automatic exchange of data between our assessment model and the 3D model of the design coming from our clients is the key for the overall efficiency of the project. It means that individual solutions can be generated, transferred and amended for future projects, according to need.”The crew, who are tasked with restoring essential systems as quickly as possible, are placed in the forefront of SRtP. Effectively emergency workers in a major event, they are a major beneficiary of easily updated manuals because they will be working with the latest information. Manuals are also vital in the regular practice drills that keep the crew in the loop.
“An onboard software tool based on assessment data allows the crew to run scenarios of casualties in a simulation environment,” says Mr Werner. “This is extremely valuable for supporting decisions, monitoring the status of an emergency and controlling actions in these situations. It is also vital for training purposes and demonstrating compliance with flag-state regulations.” It is to be hoped though that the SRtP manual never has to be used in anger in a Global-class vessel.

Source : Riviera Maritime Media