This is the second part of the longer blog post series called The Journey. The series consists of four short articles focusing on the future and sustainability of the cruise industry.

Impact of the shipping industry, specifically the cruise industry, on greenhouse gas emissions, including an overview of regulatory developments in the past decade.

PART II (this post)

How do different activities within the cruise ship contribute to the emissions?


What are the current steps taken to address some of these problems?


What are the potential future solutions and how ALFRED will help to decarbonize?


Cruise ships are sometimes described as floating hotels but we at ALFRED would like to get rid of that analogy for good. Why? Well, we haven’t heard of a hotel producing its own potable water, let alone producing the electricity it needs. To get a better analogy to use, let’s have a look at just a few of the main components onboard such a vessel.


These days most cruise ships are still powered by Diesel Electric systems, with a clear trend since 2018 to replace the diesel generator sets with the equivalent LNG (Liquefied Natural Gas) sets. Since LNG engines can also operate on marine diesel oils, they are often called Dual Fuel Diesel Electric (DFDE) systems.

In both cases the design principle is that a fossil fuel powered engine onboard produces mechanical power, which is in turn converted by the generators into electricity. The electricity is then used by the various power consumers onboard over an electric grid.

DID YOU KNOW that AIDAnova of AIDA Cruises was the first LNG powered cruise ship in the world? She was designed and built by MEYER WERFT in Papenburg and started sailing in 2018.

Such Diesel Electric configuration allows great flexibility for the architects when designing the cruise ship’s interior, since all the main components of the system can be located independently. This is primarily because the main engines don’t have to be connected / aligned with propellers over long shaft lines which would take up a lot of space.


A cruise ship’s propulsion system consists most commonly of submerged propellers rotating on a shaft that is powered by an electrical motor. A very popular choice for a cruise ship is independently rotating (Azimuth) thrusters, which allow more flexible arrangement than with a traditional long shaft line from onboard motors to the propellers.

The propulsion system’s primary responsibility is to provide the ship with the necessary thrust and maneuverability to move forward.

It is extremely hard to generalize, as cruise ships tend to operate on very varying profiles, but approximately half of the energy used onboard goes to propulsion. These days the typical itineraries are planned with a rather low cruising speed, meaning that the savings potential from this part is also rather small. Also sailing distances are in common cases relatively short, for example, between ports of call around an island group.

Furthermore, cruise ships have a very fixed route and timetable: passengers are on vacation, and they expect to leave A, and arrive to B, at certain times, as their whole vacation planning is around this schedule.


If we continue to simplify, approximately half of the remaining energy (quarter of the overall total) goes for HVAC (Heating, Ventilation, and Air Conditioning). As HVAC is such a big individual energy consumer a lot of effort has already been put into the related hardware and their energy efficiency. However, optimizing the usage of the HVAC system remains a key factor reducing the overall energy intensity of cruise ship operations.

Since cruise ships typically tend to operate in rather hot & humid climates HVAC is very important for keeping the ship’s interior in good shape. But not only that, we have to remember that the passengers are on a vacation, possibly spent a long day on a shore excursion, and want to enjoy fresh, dry, and cool air in the comfort of their stateroom.

So, let’s not turn off HVAC entirely, eh?


Freshwater generators are pieces of equipment that produce fresh water for drinking, cooking, washing, and even operating other pieces of machinery that require fresh water, for example to cool itself.

There are three primary sources for fresh water onboard a modern cruise vessel: Reverse Osmosis (RO) units, Evaporators and collection of AC condensed water. RO units, with their high efficiency, have become a very popular and primary choice for cruise ships. However usually an Evaporator is also needed, for example to produce distilled technical water.

RO units work on the principle of reversing the osmosis frequently happening in nature and forcing high pressure salty water through semipermeable membranes. Therefore, RO units require salt water and electricity to operate.

The two things necessary for the production of fresh water by evaporators are usually available in abundant quantities: seawater and heat. Fresh water can therefore be obtained by evaporating seawater using any heat source that is available; in the case of a cruise ship it usually is the waste heat from the power plant itself. 

AC condensed water is produced in surprisingly large quantities in the HVAC system. This can be utilized as an additional supply for the onboard laundry.


The biggest cruise ships can nowadays cater for close to 7000 passengers. This means that the Food & Beverage (F&B) operations of a ship are enormous to respond to the demand.

There are many pieces of equipment that are used in a passenger vessel’s galleys (that is what the kitchens are called at sea, or on a plane in air) that work together to provide catering services for passengers. It is imperative to note that if the systems are not fine-tuned to make them as efficient as possible collectively, energy might be wasted.

Keeping these vast amounts of F&B fresh means also a significant amount of refrigeration and cold storage. You can imagine how many cold Coca Colas and beers need to be chilled and served daily!



Some other energy consumers worth to mention are waste and wastewater treatment systems, lighting systems, spa & water park activities, entertainment, and in some cases even electric go-cart tracks, ice skating rinks, or attractions like FlowRider where huge water feed pumps create an artificial wave for the passenger to surf on [flowrider].

I think you might have already come up with a better analogy than a floating hotel…? At least we feel we are looking at small floating cities instead, with a full city infrastructure starting from power plants, tap water, plumbing, electricity, internet connections, movie theaters and burger joints.

Maybe this helps us understand the sheer complexity of getting all this work together smoothly, and moreover, in an energy efficient manner. Like many times, technology, such as artificial intelligence and energy management systems can help us reduce the carbon footprint of our ocean vacations.


[flowrider] FlowRider:

Thank you for reading – Please return for Part III

We would happily welcome all the feedback you might have!