While there is plenty of excitement surrounding the reduced emissions of an LNG cruise ship, there are both pros and cons of this type of fuel.

With cruise ships being under pressure to become more environmentally friendly and reduce their carbon footprint, the cruise industry has been looking for alternative energy sources for many years now.

The ongoing search for a sustainable fuel source has been accelerated over the past few years and is now showing up on LNG cruise ships.

One of the most notable changes involves the shift to using liquefied natural gas (LNG) to power cruise ships. The first LNG ship was Carnival-owned AIDAnova in 2018. Since then, 20 LNG-powered cruise ships have come to market.

Generally, natural gas tends to come from a fossil source. However, it can also be produced from the decomposition of waste products. Natural gas is extracted from the earth’s core and is cooled to -260°F, making it liquified gas. It is mostly methane but is only referred to as LNG once it has been liquified. This is done by either pressurization or refrigeration.

Refrigeration is usually the chosen method for its safety and ease of non-pressurized storage and transport. In a liquified state, it is colorless, odorless, non-toxic, non-corrosive, and cost-effective when compared to petroleum or gas. Plus, it is cleaner and easier to use in engines, requiring less maintenance time.

Turning this gas into a liquid is necessary since it reduces its volume to 1/600th of natural gas in a gaseous state. If it is not turned into a liquified state, a ship’s fuel tanks would be so large that you wouldn’t be able to carry anything on board.

Liquefied natural gas is a clean-burning fuel that cuts sulfur emissions up to 99% and nitrogen oxide emissions by 85%. The overall effect is reducing greenhouse emissions by 30%, thereby eliminating particulate matter from the ship’s exhaust. It has a low environmental impact because sulfur is removed in the pre-liquefaction process.

This means that it releases almost no particulate matter or sulfur oxides when burned. It also releases less nitrogen oxide and carbon dioxide compared to other fossil fuels.

LNG is safe since its specific gravity is lighter than that of air and it easily diffuses. This means there is a lower risk of explosion. Another advantage is that it will be a stable supply for over 50 years.

The key advantages of LNG are:

The downside to an LNG-powered ship is that LNG is a fossil fuel, which is finite. Some people estimate that with the current rate of consumption, the natural gas reserves may only last another 50 years. If we assume that additional legacy marine fuels will also become scarcer, we may find ourselves looking for another solution.

One disadvantage to this marine fuel is that it can’t be used in existing diesel or gas engines. Cruise ships need to be built using a specific engine type so as much LNG can be held as possible and it is able to burn properly.

With the lower fuel density, any LNG-fueled cruise ship requires twice the tank space. This may cost the cruise ship a few cabins, meaning fewer paying passengers.

There aren’t many fueling facilities currently in existence, so getting an LNG-powered cruise ship refueled takes planning. Although there are plans to create additional LNG fueling depots, many ships are hesitant to make the switch at present. They are willing to pay more for maintenance costs and extra fuel in exchange for the ability to easily refuel.

Some cruise ships are equipped to default to diesel fuel if they run out of their primary fuel source or if the engines fail and they aren’t close to a fueling facility.

The main disadvantages to LNG are:

The good news may be in the fact that there are other options that have some potential. These include biofuels, ammonia, hydrogen, and potentially nuclear power. However, as with most fuels, each comes with its own set of advantages and disadvantages.

It has become apparent that electricity will likely play a significant role in future fuel sources. This may not be a huge surprise when you consider innovations in battery storage in recent years. There have also been advancements in this field in the automotive industry, making the introduction to the cruise sector more plausible.

Yet cruise ships seem to be on a different scale in comparison to everything else. Batteries, while they may work, are heavy, which is a large consideration when you consider that a ship must remain afloat. This means that mega-ships will probably not be exclusively powered by electricity anytime soon.

While companies like Eco Sightseeing are using Tesla batteries to convert a passenger boat to electrical propulsion, using this technology on a larger scale would involve incorporating 10,000 Tesla S85 batteries daily. Yet, as batteries become smaller with an expanded capacity, this may be plausible in the future.

One such example is the Yangtze River Three Gorges 1, which has been named the largest electric cruise ship in the world.  It recently completed its maiden voyage from the home port of Yichang in China’s Hubei Province. The ship is 100 meters in length and has zero emissions.

It can carry 1,300 passengers in a single voyage and is electrically powered by batteries with a total of 7,500kWh (100 EVs).

While these advancements are promising, the ships can only run for short durations and aren’t suitable for long voyages.

LNG cruise ships have both benefits and disadvantages despite the rosy picture that is often depicted. While they do have less harmful emissions, the cost of implementing them, in addition to the lack of bunkering facilities, has served as a deterrent for some time.

However, with the desire to become more environmentally friendly, many cruise lines are making the move to LNG-powered vessels.

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