“Floating cities” require great power to navigate but above all very sophisticated technology for every need. Let’s see how these giants of the sea work, as tall as buildings and as long as several football fields
To understand that it is limiting to define a giant of the sea like Costa Smeralda as a ship (even if technically it is), a few numbers are enough. The length of Costa Crociera’s flagship, together with its sister ship Costa Toscana, is 337 metres, more than three football fields placed side by side; the width of 42 meters. The height is 63 meters, like a twenty-story building. And in fact there are 19 floors of the ship (what in jargon are called bridges), all connected by different blocks of elevators for a total of 20 systems, counting only those open to the public. The gross tonnage is 185 thousand tons and inside there is space for 2,612 cabins for a total of over 6,500 passengers to which must be added the crew of 1,700 people. Costa Smeralda was launched in December 2019, in Turku (Finland) where it was built, and christened on 22 February 2020. We took it as an example to understand how the large cruise ships that are increasingly becoming most numerous and crowded in the world. Authentic “floating cities” which on the one hand offer everything and more to guests (catering, hotel services, entertainment) and on the other are technologically cutting edge like very few other objects that move in the sea. In this specific case, Costa Smeralda sails at a cruising speed of 17 knots (31 km/h) when a Nimitz-class aircraft carrier of the US Navy, practically the same length, can reach 30 knots (56 km/h) but with a notable difference: it weighs just over half of the Costa Crociere ship and is powered by two nuclear reactors.
azipod magic
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To be able to navigate well, often with eight thousand people on board, you need not only a lot of power, but the right one at the right time. Costa Smeralda is equipped with four Caterpillar generators that produce electricity for all the ship’s needs: from propulsion to on-board services. Each of the four generators has 16 V-shaped cylinders and develops a power of approximately 21,000 HP (approximately 15,440 kW): therefore in total 84,000 HP (61,760 kW) are available. The energy necessary for propulsion is transferred by generators to two propellers, each of which has a diameter of 5.95 m, mounted on the so-called Azipod. Technically it is a marine propulsion unit consisting of a fixed pitch propeller mounted inside a steerable casing (the podin fact) which also contains the electric motor that drives the propeller which, in the Azipod propulsion system, has a fixed pitch and variable speed. Their peculiarity is that they can rotate 360 degrees around the vertical axis, with enormous advantages in maneuverability compared to traditional propellers. During manoeuvres, the Azipods mainly move the rear part of the ship while at the bow we have four maneuvering thrusters (called bow thruster) of 3,500 kW each, equal to 4,759 HP. They serve to give lateral thrust to the ship.
THE ADVANTAGES OF GAS
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Costa Smeralda fuel? The generators are powered by LNG, i.e liquefied natural gas: less polluting than diesel and fuel oil, today it is the best technology in the cruise sector and can be used on a large scale, because in addition to reducing CO2 emissions compared to conventional fuels, it almost completely avoids emissions of nitrogen oxide, sulfur and fine dust. The three Costa Smeralda tanks contain a total of approximately 3,200 cubic meters of LNG. The appeal to diesel This only happens in the event of limited gas supplies available on board, in fact it is a backup solution. The only problem with LNG is that to maintain its liquid form it must be stored at high pressure and in any case below -100 degrees centigrade. Appropriate regasifiers bring it back to the ideal state to power electricity generators. When the ship is cruising, depending on the conditions and speeds required by the bridge, the energy demand is normally met with three generators in operation, which allows one generator to always be kept off for any maintenance operations. When the ship is stationary, a single generator is needed to keep all on-board services active, active even below 50% of its nominal power during the day, while in the evening it can go to around 60%. As the ship’s electricity consumption grows, in the engine room they balance and anticipate requests by activating more power on the generators.
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THE MOORING
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One is truly surprised to see how a giant like that comes operated relatively easily. To get to the command bridge of the Costa Smeralda you must be categorically accompanied by someone authorized to enter the “restricted” area, which is protected (obviously) with sophisticated access control systems. The deck space is boundless, given that it occupies the entire width of the ship, from side to side, and the fact that it is a open space and the control instruments are concentrated in the central part, it emphasizes this effect. The captain and his seconds sit on the bridge: there are many medium and large (not huge) displays, dozens of touch keys and buttons, a joystick – incredible how small it is considering a 185 thousand ton ship, which is used to directionality, the “handcuffs” that maneuver the power to be sent to the two stern propellers and the rotors for the four bow thruster of the bow. From here you can also control the two stabilizing fins which come into operation in case of rough seas. There is no shortage of a small traditional helm and a romantic one compass analogue, but practically all maneuvers are performed by operating the aforementioned joystick or servo-controlled controls. Unless you encounter demanding conditions, mooring is essentially the only complicated maneuver for those sitting on the bridge: here human intervention is still important while detachment from the mainland is easier, without prejudice to the fact that one is always impressed by the maneuverability in protected basins of a “boat” almost 340 meters long. The central controls are repeated on the two fins of the bridge, which allow you to pilot even with a careful look at the side of the ship. And below too, given that part of the floor is glazed for this very purpose. With the support of instrumentation and very sophisticated technology, it is possible to moor the ship with a maximum displacement of 10 cm compared to what was expected. But even with all the modern assistance systems – including the slew of alarms and the autopilot which is the absolute protagonist during navigation – the seaman’s “handle” is still indispensable here.
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