The interior design of a cruise ship is an important element in attracting passengers and creating brand image. The interior outfitting also has a big impact on technical, economic and safety considerations in the design of large cruise ships.

For operators, big ships mean economies of scale through increased passenger capacity. Passengers have also shown a growing interest in larger ships because of the greater number of services they offer. Cruise liners and ferries have excellent safety records. However a few accidents can turn public opinion.

The International Maritime Organization (IMO), flag state authorities and safety organisations cooperate to increase the safety standard, and new principles have been approved for safety assessment that give the naval architect more freedom when working on design.

Cabin considerations

The starting point for cruise ship design is addressing passenger facilities. What size and type of cabins is to be offered, what food service, entertainment and activities? The naval architect must understand passenger expectations and propose new solutions and improvements that the operator might not be aware of. Cabins are the most important design element.

Cruise ticket pricing is based on cabin size and location. Passenger cabins are the most expensive items in cruise ship construction. However, it is important not to forget that the public facilities and services onboard influence passengers’ choice of ship. Impressive interior design for both cabins and public spaces has become a very important factor for customers choosing between cruise brands.

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“The naval architect must understand passenger expectations and propose new solutions and improvements that the operator might not be aware of.”

There are strict rules for passenger ship safety that must be followed in the design process. The IMO has defined the goal designers should be aiming towards as making ‘the ship itself the best lifeboat’. This means that in an emergency both passengers and crew should be able to stay safely onboard as the ship proceeds to port.

The naval architect must also consider the ship’s functions, for the passengers and for the service crew expected onboard. The layout of passenger cabins and public spaces should be coordinated with the ship’s fire zones. Passenger and crew stairways also serve as escape routes.

Major horizontal walkways or corridors must be above the bulkhead deck, because watertight doors are kept closed at sea. In a large cruise vessel where the beam exceeds 40m, it is simply impractical to keep the main fire zone area below 1,600m². IMO provides an equivalence approach to deal with this problem.

Damage stability

The new rule for damage stability is based on the probability of damage occurring to the hull. This is arrived at by analysing the length, penetration and vertical extent of the damage reported from previous ship collisions and groundings, and calculating from this information the probability that the ship will survive.

This must be higher than the required index specified in the IMO rule. The index increases with the number of persons onboard and the length of the ship.

The index also depends on lifeboat capacity. Most cruise ships are built for long international voyages with lifeboat capacity for at least 75% of all passengers onboard. For the remaining 25% life rafts or marine evacuation stations are provided. For a large cruise ship with 6,000 people onboard, the required index is approximately 0.85.

Steel structure and Propulsion

The steel structure of a large cruise ship is very complex. There are decks and bulkheads and lots of openings for doors, stairways, lifts and ducts that can weaken the structure. The deck above large public spaces must be supported by large beams and pillars. In the superstructure the steel plates are very thin – sometimes only 5–6mm – to save weight and improve stability.

The steel structure is optimised for strength and stiffness by the finite element method, where every plate, frame and beam is mathematically modelled and tested under different loads. The IMO stipulates that, in the event of an incident, passengers and crew should be able to stay onboard so that the ship can proceed to the nearest port. For this to be possible, cruise ships require a back-up power supply and propulsion.

With diesel-electric machinery, this can be secured by locating the diesel-generators in two or more engine rooms, separated by watertight and fire-insulated bulkheads. All auxiliary systems must be divided in the same way. A safe solution is to place the diesel generators in two separate main fire zones and have separate engine casings all the way to the funnel.

The propulsion must consist of at least two units, located in protected compartments. In Voyager- and Freedom-class cruise ships a triple pod solution is used, with two steering and one fixed pod unit.

Lifesaving appliances

The lifeboats and life raft stations occupy a great deal of space along the embarkation deck on a large cruise ship. Passenger capacity grows proportionally more than the ship’s length when ship size is increased.

“For a 200,000 gross ton ship with 6,000 passengers and 2,000 crew onboard, there is little space along the lifeboat deck for traditional lifeboats and other lifesaving appliances.”

For a 200,000 gross ton ship with 6,000 passengers and 2,000 crew onboard, there is little space along the lifeboat deck for traditional lifeboats and other lifesaving appliances. The biggest lifeboat used today is intended for 150 persons. If two 150-person lifeboats are combined into one boat for 300 persons, the space demand can be reduced and the lifesaving appliance capacity increases to the required 8,000 persons.

The use of larger lifeboats must be approved by class and flag state following the equal safety principle. In creating the new generation of cruise ships, naval architects and interior designers need to work together. They must build on the experience of previous designs but also look for new technical possibilities that can improve the performance, environmental friendliness and safety of the new ships.

How can passenger capacity be increased? What layout gives the maximum balcony ratio? Can fuel consumption be reduced? What hull form has the best sea-keeping characteristics? How will new solutions affect building costs? These are all important questions for the naval architect.

The most important question, however, is how to understand customers’ demands and expectations. Both the naval architect and the interior designer must look at the ship from the passenger’s point of view to be able to create a winning design for a new and impressive generation of cruise ships.