Carnival Splendor is an example of Concordia class ships.
From Costa Concordia deck plans:
Costa Concordia (built 2006, scrapped in 2015) was the first of all five Concordia-class liners operated by Costa Cruises - together with the sisterships/fleetmates Costa Serena (2007), Costa Pacifica (2009), Costa Favolosa (2011) and Costa Fascinosa (2012), plus the Carnival Cruise Line's ship Carnival Splendor (2008).
From a US Coast Guard investigation into a fire in the engine room (p14):
The Carnival Splendor has two engine rooms: the forward engine room and aft engine room. Diesel Generators (DGs) 1, 2 and 3 are located in the forward engine room. DGs 4, 5 and 6 are located in the aft engine room. The engine rooms are separated by a watertight bulkhead.
This a tad better quality than other images of Deck C. US Coast Guard clearly identify Watertight Doors. Watertight bulkhead (in Red) is shown.
From Costa Concordia - Damage and Stability:
Hull damage length of 53 metres (from frame 52 to 125) and variable width up to 7.3 metres.
From boatdesign.net Simulating Costa Concordia:
Damage (in Red) was across both engine rooms (five watertight compartments). So initial flooding would of taken out all electricity, except for the Emergency Generator (1.5MW), which would only supply Emergency loads (some lights, steering gear, bilge pump, fire pump, communications, elevators). Hole was too large for bilge pump and fire pump (which would have to be reconfigured for pumping damage water) to do anything.
Edit: Apparently, Emergency Generator started but failed. So vessel had no power.
The Sinking of a Ship
21:46:05 the emergency generator that provides power starts only for 41 seconds.
If there was a separation of forward and aft engine rooms, ship would of had some power, but initial damage was too extensive for 50% generating capability to have any major impact on accident or evacuation of the ship.
When you hit a rock at speed, it is just physics. Movable ship meets immovable rock!
The Carnival Splendor has 6 12.6MW generators producing 75.6MW of power. The largest load is 2 21MW propulsion motors requiring 42MW of power.
This means there would be a large current from the generators to switchboards to propulsion motors. To limit current, switchboard and generators will be at a high voltage 11kV. Transformers will step-down voltages to 440V for motors, pumps and 120V (or 240V) for outlets, lights, with a possible intermediary voltage (690V) for some pumps, thrusters, or compressors.
With electric propulsion, generators can go anywhere on the ship. But the reality is Generators and Main Switchboard will be close to Propulsion motors to minimize length of conductors and keep 11kV conductors protected (channel).
The switchboard is radial architecture (Generators - Switchboards - (Distribution Panels) - Loads). The Carnival Splendor (fire between switchboard and generators) and Costa Concordia (hull breach with generators in adjacent compartments) demonstrate the problem with this arrangement, loss of power if something bad occurs.
When cruise ships sailed, it seemed like at least one cruise ship would lose power for a significant period each year (2019: Viking Sky; Vasco da Gama; 2018: Star Pride; 2013: Carnival Triumph; 2012: Costa Concordia; Costa Allegra; 2011: MSC Opera; 2010: Carnival Splendor). So the problem does occur.
An alternative switchboard arrangement is ring, where switchboard is split into a circular ring with interconnects, so that loss of a compartment, or multiple compartments, does not cripple ship. Thrusters / Generators are connected to individual switchboard components. For true redundancy, two generator rooms in stern AND bow would be required. Loss of any compartment or multiple compartments allows isolation. Capabilities of vessel are decreased, but power system will work in some fashion.
Ring distribution is already used in millitary vessels and vessels (offshore supply and feeder tankers) with DP3 (dynamic positioning). DP3 vessels position themselves close to drill ships or platforms, so must have a FMEA (failure modes and effects analysis) plan so if something fails, the steps to keep the vessel in position are already known. If this fails, do that.
From Better Ship Electric Arrangements:
As reported by Better Ship Electric Arrangements, based on Costa Concordia, IMO (International Maritime Organization) is promoting alternative powering arrangements for passenger ships. Hard to say what alternative powering arrangements actually means for a ship designer or a country's marine regulatory agencies or certification agencies.
As for costs, that is a little harder to say/guess. A ring switchboard would require additional breakers for cross-over or ring connections and a high-voltage copper conductor ring going around the ship. This additional cost would be offset by a decrease in copper costs, as smaller conductors would be used connecting individual loads to the power system because cable runs would be shorter, and alternative construction methods. Regulations require an unspliced run from source to load or distribution pannel. So if the distribution system is distributed, modular construction with shorter modular wiring, glanding (waterproofing wires penetrating bulkheads), fire protection is easier, which is cheaper. Instead of wiring in shipyard, modules can be built off site and only main ring would have to be connected in the shipyard.
So additional costs, but opportunity for time savings and less copper. Equivalent???
Better Ship Electric Arrangements references "Zonal Distribution Cuts Cabling Cost” by John Hensler of STX Marine. From the abstract for the paper:
Modular construction is the accepted norm in the shipbuilding industry. Modularization allows pre-fit of many systems and equipment. Cabling, to a large extent, is one of the exceptions to modularization. This is a major limitation in the way of maximizing construction efficiency. A mid-size offshore support vessel is fitted with some 300 km of cables which
translates into significant cost and installation time scheduling implications. Installing cables is a highly labour intensive process. Cables have to be pulled one by one through sheaves and pulleys, lead through tight spaces and hard to reach openings. The root cause of having to rely on cable pulling technique for installation is the nature of the philosophy for power distribution. Power is distributed from a strategically positioned main switchboard directly to large loads and via feeder circuits to distribution panels and MCCs. Because all of these conductors originate from a single centre, this kind of distribution philosophy is known as “Radial”. In a radial concept, cables run long distances from the central point of distribution to remote consumers. The net result is a large number of cables to be pulled throughout the ship. The zonal distribution philosophy emerged as a method for fault tolerance, improved availability and better survivability for naval applications. Side benefits of the zonal distribution method are lesser quantities of cables, which is a cost saving measure on its own, and suitability for modular installation. The zonal distribution system treats each construction module in a manner, analogous to a district substation in a land based power grid. This analogy explains how all consumers installed in that module can be prewired and then hooked up to the bus though a single, redundant point of connection. Because a module is typically limited in its physical extent, many cables can be “walked” into location, as opposed to pulling. In fact, most main cable ways can be preassembled in the form of harnesses and hence entire groups of cabling can be installed by a single “walk”. A side benefit of localizing cable runs within the boundaries of construction modules is the ease for electrical isolation in case of a fire or flood incident affecting the module.