The average speed of cruise ships is 20 knots (23 mph, 37 km/h), and the current fastest cruise ships are the MV Glory Sea ship and the Queen Mary 2 ship, both of these vessels can achieve a cruise speed of 30 knots (35 mph, 56 km/h).
The maximum speed ever recorded by a passenger ship is 39 knots (44.87 mph or 72.24 km/h) but this was achieved by the SS United States which is technically an ocean liner and not a cruise ship.
In this article you’ll learn more about the speed of cruise ships and the factors that influence how fast these impressive vessels can break through the waves.
What is a Knot?
A knot is a unit of speed used in maritime and air navigation as well as in meteorology.
1 knot is equal to 1 nautical mile per hour, or 1.15 mph and 1.852 km/h.
How Did the Knot Become the Measuring Speed of the Seas?
Ancient sailors measured the speed of their moving ships by throwing a floating object into the sea and then counting the time it took to pass the ship’s stern using a particular type of sandglass. Called the Dutchman’s log, this device became the standard tool for measuring speed until the 16th century.
At the end of the 16th century the Dutchman’s log was replaced by a newer device called the Chip log.
In this chip log, knots were tied at equidistant intervals in a rope and on the end of the rope a piece of wood was attached to it. To measure the speed of a boat, mariners used to toss the end of this rope behind the ship and allowed the rope to roll out freely.
By counting the knots that passed over the bow within a certain time, sailors measured the ship’s speed. For example, a ship traveling at 10 knots was said to go 10 nautical miles in an hour.
What is the Difference Between Top Speed and Cruising Speed?
Cruise ships often choose a cruising speed or service speed that is comfortable for passengers. This will be somewhere below the fastest possible speed the vessel can reach. The cruising speed also takes fuel consumption into account.
The top speed of ships differs from their comfortable service speed. The route of a particular ship affects its speed, and cruise ships rarely travel at a speed that would make it uncomfortable for passengers. Also, traveling at the fastest possible speed with all engines open would hurt efforts to conserve fuel and travel efficiently.
For closer ports, captains may opt to travel more slowly. For farther destinations, a ship may take on additional speed in open waters where it can travel more efficiently.
Sometimes, ships float or idle to allow guests to enjoy scenic venues. In Hawaii, cruise ships often pause to let passengers take pictures of erupting volcanoes. Similarly, cruise ships in Alaska pause for weather and glaciers for safety reasons.
What Was the Fastest Cruise Ship in History?
Launched in 1969, Cunard’s Queen Elizabeth 2 faithfully toted passengers until it was decommissioned in 2008. The QE2 was intentionally built to be the world’s fastest passenger ship. Her service speed alone was over 28 knots. To reach this heady speed, the ship used only seven engines. This left two in reserve to allow for non-disruptive maintenance. Reputedly, the QE2 had a top speed of 34 knots.
This speed came at a cost. The 963-foot ship took one gallon of fuel to move forward 50 feet. With 10 gallons of fuel, she could travel 500 feet.
- Top Speed: 34 knots or 39 mph
- Displacement: 49,800 tons
- Capacity: 2,900 passengers and crew
- Status: Now a floating hotel in Dubai
Launched in 2004, the Queen Mary 2 is Cunard’s new flagship. At that time, it was the longest and biggest ship in the world — a title now held by Royal Caribbean’s Freedom of the Seas. It was the longest and largest ship on the oceans. The QM2 is the only transatlantic cruise ship currently in operation, and it offers one annual cruise that crosses the Atlantic. The mega-ship is still the largest ship under commission, with a service speed of 26 knots.
- Top Speed: 30 knots (34.5 mph)
- Displacement: 79,300 tons
- Capacity: 3,950 passengers and crew
- Status: Still in operation
How These Giant Cruise Ships Can Move Themselves?
Diesel reciprocating engines power older cruise ships. The engines supply the power to turn propeller shafts that move the boat by displacing water. A transmission system connecting the engines to the propellers determines how fast the propellers move, thus the speed of the boat.
Many modern ships use gas turbines or diesel-electric engines to propel the boat and power shipboard systems. Larger ships may incorporate two power sources for propulsion and electrical power, respectively.
Gas turbine engines create heat and transform it into mechanical energy to produce electricity. In a combustion chamber, these engines compress hot air. The hot exhaust is used by a turbine that spins a shaft that in turn spends the generators. This is similar to how diesel-electric engines operate. The output shafts connect to generators to create electricity.
Both these engines gobble up tons of fuel. The QE2 used 380 tons of fuel every day to achieve 29 knots per hour. The large ship carried enough fuel to last 12 days between ports. Usually, ships use fueling barges to fill their tanks or top up at their ports of call. Using lower-grade diesel, the powerful engines that power these boats are not as efficient as diesel used in cars and trucks.
Currently, all cruise ships use propellers or screws to push the vessel through the water or to go in reverse. Airplanes require very fast propeller speeds to move through the air. However, ships rely on torque power, move more slowly, and rarely top 30 knots due to the effect on the passengers and crew.
Cruise Ship Fuel Usage: Size Vs. Efficiency
Size affects fuel consumption and, therefore, efficiency on cruise ships. Smaller ships consume less fuel for trips of the same distance. The average speed also impacts fuel consumption, a fact any captain is keenly aware of. The average ship uses 250 tons of fuel per day. That’s a whopping 80,000 gallons per day or 800,000 gallons for a 10-day trip!
Just like a car on the highway, higher speeds for ships create aerodynamic drag. This requires more fuel to maintain the same speed. Most cruise ships maintain a speed of 21 to 24 knots to avoid aerodynamic drag that could eat up the ship’s fuel supply. Running out of gas in the middle of the ocean is obviously not an option.
In general, cruise ships up to 1,100 feet long must carry as much as two million gallons of fuel to make the trip between ports of call. In comparison, a private motor yacht that’s 60 feet long carries up to 1,200 gallons while the Exxon Valdez holds 55 million gallons of fuel.
Royal Caribbean’s Harmony has four-story-high engines. It burns through nearly 1,400 gallons of fuel every hour. That’s 66,000 gallons every day, which creates a lot of pollution. In recent years, there has been enormous regulatory pressure to make big ships friendlier to the environment and the ocean that they sail on.
What Impacts the Speed of Ships?
Assuming a cruise ship is optimally designed for weight load, its speed will be the square root of its horsepower divided by weight. However, operators who want to improve their speed cannot just offload some weight and expect to achieve maximum speed. Where the weight lies matters just as much. For example, front-loading the boat creates drag and slows it down.
Besides, traveling at top speed doesn’t present the most comfortable ride for passengers. That’s why captains take their time and travel at comfortable average cruising speeds.
Here are several factors that impact how fast a cruise ship goes:
Cruise ships crossing the Gulf of Alaska often slow down to let passengers share close encounters with the magical sea life in the area. Sometimes, ships have to slow down because of unfavorable sea conditions that cause rough water and high waves. At other times, cruise ships slow down for beautiful views of coastal cities and natural attractions such as volcanoes.
Passengers may also note that boats slow in shallow water such as that found close to harbors. This prevents the boat from unexpectedly running into objects at low tide or in shallow seas. In open water, ships often move much faster toward faraway destinations. There’s more room to maneuver in deep water far away from populated areas.
2. Weather Events
Just as heavy wind and rain impact how fast a car can go on land, the weather at sea greatly impacts the speed of cruise ships. The direction of the wind can improve the average speed of a boat if it comes from astern, or behind the boat, pushing the cruise ship in the direction it’s traveling. On the other hand, a headwind pushing against the bow or front of the boat can significantly slow it down, requiring more energy to travel at the same speed. Wind shear from wind hitting the boat from either side creates drag and makes it harder for the boat to move forward, consuming more fuel than a calm sea or one with a lucky tailwind.
Captains often decide to idle in position or increase speed to wait out or outrun a storm.
Thankfully, emergencies don’t happen all that often on the high seas aboard a cruise ship. If someone falls off the boat, the ship has to slow down and turn around to attempt to rescue. Sometimes, another vessel requires assistance, and the crew prepares the boat for top speed to answer the SOS. In case of an outbreak of illness or disease on board, ships sometimes must anchor offshore or cruise around until they are cleared to enter their port of call.
4. Fuel Conservation
Moving at slower speeds helps to conserve fuel. Ships drilling their way through the water experience more resistance than a car cruising down the highway. This results in monstrous energy consumption and big boats burn through fuel fast when traveling at top speeds.
Imagine a cruise ship that requires nearly 225 tons of fuel every day to achieve an average cruising speed of 24 knots. By decreasing its speed by three knots per hour, this ship could save 75 tons of fuel a day. With potential savings in fuel and cost of 33%, slowing down is better for the environment and the owner who writes the check to the fuel company.