Cruise ships travel far distances carrying anywhere from 100 to 6,000 passengers, depending on a vessel’s size. Some ships cross the Atlantic and the Pacific Oceans, which are both thousands of miles wide. Considering there are no cruise ship “gas stations” along the way, how do these vessels transport their guests to such exotic places and make it look so effortless?
If you’ve ever thought about cruise ship fuel consumption, you likely have a lot of questions. Cruise ships are engineering marvels that complete incredible feats — like taking passengers from St. Maarten to Barcelona while they swim, dine and lazily watch the sea pass by. But while guests enjoy life onboard and its many pleasures, the crew keeps the ship fueled and powered behind the scenes. In this post, we’ll answer a few common questions about cruise ships and how much fuel they use. As you’ll see, a vast range of factors impacts fuel usage.
How Much Fuel Does a Cruise Ship Use?
The most straightforward answer to this question is that small ships consume a much lower amount of fuel than large ships traveling the same distance. According to the College of Engineering and Applied Science at the University of Colorado Boulder, a large ship might consume up to 250 tons of fuel per day. To put that in perspective, that’s equivalent to over 80,000 gallons of fuel a day. Regular-sized ships, by contrast, may use up to 150 tons of fuel per day. As vessels shrink in size, so does their fuel consumption. In general, a more massive object requires more power to get moving. That power comes from fuel.
What Is a Large Cruise Ship?
While cruise ship size definitions vary, generally, large vessels are those that carry more than 2,500 passengers. Medium-sized ships carry around 1,500 passengers, give or take. Small ships typically transport fewer than 800 passengers. Windstar’s ships are on the smallest end of this range, as our vessels carry roughly 250 to 300 guests.
How Much Fuel Does a Cruise Ship Hold?
A large cruise ship ranging in length from 900 to 1,100 feet might hold 1 to 2 million gallons of fuel. Smaller vessels, like a 440-foot-long ferry, might carry around 130,000 gallons of fuel, while a gigantic ship measuring over 1,300 feet in length can tote over 4 million gallons. Windstar’s largest vessels measure less than 600 feet long, so, as you might imagine, require much less fuel than the typical cruise ship.
How Does a Cruise Ship Refuel?
Any operator of an ocean-going vessel, such as a passenger cruise ship, relies on the fuel availability at the ports where they travel. Fortunately, according to the California Air Resources Board (CARB), over 400 ports around the world offer marine fuel. When it’s time for a cruise ship to refuel at a port, a small boat, called a barge, brings more fuel to the vessel. The process, called bunkering, takes the work of a team.
Although the method of refueling can vary somewhat, it generally follows these steps:
- The barge secures to the side of the cruise ship.
- Workers connect a hose from the supplier’s tank to the ship’s tank.
- The crew pumps fuel into the tank to the desired level.
To better illustrate this process further, consider the Louis, a Canadian icebreaker ship. The vessel’s tank can hold about 1 million gallons of fuel. During refueling, a barge will pump about 110 tons of fuel into the ship every hour.
Factors That Affect Fuel Consumption
If you regularly drive a car, you likely notice how different factors affect the amount of fuel you consume. For example, if you decided to go on a road trip with your truck towing a boat, you probably had to stop for gas more often than the last trip you took with your vehicle alone. If you’ve ever had an experience like this, you can agree that carrying more weight requires more fuel.
The same idea applies to ships. However, unlike cars, ships also have to sail forward against various sea conditions, along with other unique factors. Here are some of the main elements that impact fuel consumption in cruise ships.
Speed is a major factor in how much fuel a cruise ship consumes. Generally speaking, the faster a cruise ship goes, the more fuel it burns. For this reason, cruise lines aim to travel at a leisurely pace from port to port, giving their guests a chance to absorb the scenery. CARB estimates fuel use to be about 80% of a cargo ship’s operating cost, for example.
Speed has a significant impact on fuel consumption, due to the power needed to drive ships forward. If you imagine the energy it takes to set a massive vessel in motion, as it faces wind and water resistance, it’s easy to see why acceleration takes more force and burns higher fuel with speed. A smaller ship, like a Windstar vessel, does not require as much energy to set sail. Nevertheless, cruise ships must maintain a minimum speed to operate.
How fast does a cruise ship go? The average speed is about 20 to 25 knots, according to the International Maritime Organization (IMO). A knot is a unit of speed equivalent to one nautical mile per hour or 1.15 land-measured miles. In other words, most cruising vessels sail at around 23 miles per hour.
Going even slower, or about 18 to 20 knots, saves more fuel. Traveling at a speed slower than 20 knots is “slow steaming,” and it’s a highly effective way to reduce fuel consumption. For example, according to the American Bureau of Shipping, a 10% reduction in speed allows the ship to save about 20% in fuel. Windstar captains cruise at around 15 knots.
The max speed a cruise ship can reach is about 30 knots. However, captains mostly avoid going as fast as possible, because it’s less efficient and may make a rougher ride, depending on the sea conditions. But, under some circumstances, such as moving away from a storm, the captain might hit full speed.
The further a ship travels, the more fuel it’ll need for the journey. Depending on its size, a cruise ship might burn a gallon of fuel for every 30 to 60 feet it travels, according to the University of Colorado Boulder. So, imagine you sail from New York to London. Let’s say that’s a distance of about 3,342 nautical miles. One nautical mile is approximately 6,076 feet. Therefore, a cruise ship sailing one way to London from New York would consume around 338,000 of fuel to make that trip.
In contrast, a ship traveling from San Juan to St. Thomas would go around 70 nautical miles and would use about 7,088 gallons of fuel. Though these numbers aren’t exact and don’t account for other factors such as speed, they demonstrate how distance makes a difference regarding fuel consumption.
As mentioned, a large vessel needs a lot of fuel to power through the water and stay afloat. A small ship can get by on much less fuel while covering the same distance. For example, a huge cruise ship might weigh close to 70,000 tons. This type of vessel is going to burn more fuel than a small ship that’s half its size because it’s going to need to displace a lot more water to maintain its buoyancy.
It’s hard to imagine any size cruise ship floating as if it were weightless across the water, but that’s part of the engineering magic. Cruise ships stay afloat as long as they can displace, or push aside, the same amount of water as their weight. By combining displacement with powerful engines, these passenger boats can move along smoothly. Smaller vessels generally use the same mechanics as the big ships, but burn less fuel in doing so.
Cruise ships use either gas turbines, diesel-electric or diesel engines for propulsion and electric power. Diesel engines are the most traditional type. With this type of engine, the diesel fuels the pistons and crankshaft, which attaches to the propeller and ultimately moves the ship forward.
A diesel-electric engine connects to generators that provide electricity to turn the propellers and power the ship’s lights, appliances, air conditioning systems and more. Most modern cruise ships have several engines connected to generators. For example, Wind Surf has four diesel-electric generating sets. These engines operate efficiently, no matter the ship’s speed. Gas turbines function in a similar way to diesel-electric engines.
Most passengers aboard a cruise ship won’t get to see the engines. That’s because ships need their heaviest weights located at the lowest point possible, so their engine rooms are near the bottom of the vessel. Since engines must power ships through the water, they can be immense for massive vessels. For example, a nine-cylinder engine designed for a large cargo ship might be 65 feet long, 60 feet high and weigh about 1,500 tons. An engine of that size would take up about one-fifth of Windstar’s small 148-guest ship.
Larger vessels require heavier engines than small ones, which will ultimately add weight to the ship and need more fuel to carry.
Envision a sports car with a sleek, aerodynamic design. Why do car manufacturers need to keep aerodynamics in mind? According to NASA, objects that have rounded or narrow surfaces tend to have less drag than flat, broad surfaces. Drag describes the force that attempts to slow a moving object down. The more surface there is for the air to hit, the more drag it creates. Such a car has an easier time reducing drag and “slipping” through a wall of air. An aerodynamic vehicle also has less trouble accelerating on a very windy day than a car with a bulkier design. As a result, the engine doesn’t have to struggle to push through the air and will use less fuel to ride.
You might think of ship design the same way. However, water causes more drag than air. Therefore, ship designers consider how both the forces in the air and water impact fuel consumption to design more efficient ships. By optimizing the hull form and surface, as well as the propellers, a boat might use up to 8% less propulsion fuel. The hull is the main body of a vessel. Ships also make an effort to keep the hull clean. Removing slime, depending on how much buildup there is, can yield anywhere from 7 to 30% reduction in propulsion fuel consumption.
Some small cruise ships, like Windstar’s Wind Surf, are sailing ships. Wind Surf combines diesel-electric engines with wind assistance to help save fuel and provide guests with a memorable ride.
Lastly, varying weather conditions make an impact on fuel consumption, particularly wind and wave strength and direction. For example, according to the IMO, a slight increase in wind hitting the front of a vessel could result in a 4% rise in fuel consumption. Sidewind could boost fuel consumption by 2%, and tailwind by 1%. To avoid poor weather and higher fuel costs, the captain may choose a different route. Usually, the fastest route will also use the lowest amount of fuel and encounter the least amount of weather-related damage.
You might think back to the Louis, the Canadian icebreaker ship we spoke about earlier, as another example of how the environment and weather conditions affect fuel use. When traveling through open water, the Louis burns about 7,925 gallons a day, or 330 gallons per hour. When it’s moving through thick ice and needs to use all five of its engines, the amount of fuel consumption increases to nearly 24,000 gallons of fuel per day.
Contact Windstar to Learn More
It’s easy not to think about the workings of a cruise ship when you’re about to dock in Bora Bora, but it might be something you’ll consider when it’s time to find a cruise line you’re excited to journey with. At Windstar Cruises, we’re thrilled to share the complete cruise experience with our guests, and invite them to speak with the captain to learn more about their vessel. We’re also proud to take our guests to the most breathtaking destinations around the world, including hidden harbors, aboard our small, elegant ships. All our ships carry no more than 350 passengers, and we cruise at comfortable, scenic and fuel-saving speeds.
Still have more questions about cruise ship fuel or vessel options? If so, reach out to us, and we’ll be happy to share our knowledge with you.
Image by Tips For Travellers
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