Diesel engines do not propel modern cruise ships, but cruise ships still carry huge diesel engines. That poses an obvious question – What gives?
“There is no more direct connection between a propeller and an engine,” says Nick Rose, Royal Caribbean’s environmental regulatory and sustainability manager. “All of your modern-day propellers are driven by electric motors. Therefore, all your engines produce electricity.”
To break it down further, before the early 1990s cruise ships were driven by diesel reduction – the diesel engine drove a reduction gear directly connected to the propeller shaft, so the engine was turning the propeller.
Now the diesels drive powerful generators that send the electricity they create to a “switchboard” that consolidates and distributes power to onboard consumers. In short, the ship is essentially a mobile power plant with its own electrical grid.
About 60 percent of the electricity goes to propulsion, whether Azipods or other means. HVAC is the second largest consumer, and then the rest of the hotel operations, including everything from lights to cooking equipment and theater shows. All mechanical equipment uses juice, including pumps and water generation.
And while it’s all electrical, it takes diesel fuel to produce it, the cost of which is second only to human capital in Royal Caribbean’s operating expenses. So the less electricity used, the less fuel burned and less emissions resulting from it.
“Everything we do or everything we’re trying to do is to consume less fuel, which in this case is consume less energy,” Rose explains. “Class over class, every five years ships average around 15 to 20 percent more efficient than the class built before it. As an example, Harmony was 20 percent more efficient than Allure was, and they’re five years apart.”
Some of the ways RCL keeps squeezing the most from the electricity created on board include:
- Replacing a single massive chiller for all HVAC needs with separate localized units, which themselves have become more efficient over time.
- Extensive use of highly efficient LED lighting.
- Replacing one-speed pumps with VFDs, or Variable Frequency Drives, which operate according to the load required. “That’s a big one,” Rose says. “We’ve been putting VFD drives on many of our ships, even retrofitting it back because it’s a way of reducing energy that’s not a huge capital investment.”
Replacing energy-hungry “flash evaporation” to transform seawater into potable water, with reverse osmosis in which seawater is pushed through a semipermeable membrane that filters out contaminants large and microscopic. That push requires far less energy than boiling water for evaporation.
While solar power might seem an obvious addition to RCL’s neverending campaign for energy efficiency, Rose says it’s not yet practical because there is not enough usable space to hold a large array of panels.
Incorporating solar cells into window glass – of which cruise ships have plenty – is not yet practical.
“The glass is close, growing quickly, but it’s just not there yet,” Rose says. “That’ll be the next big breakthrough.”