If you’re about to board a fabulous ship and embark on a once-in-a-lifetime ocean voyage, you might be wondering how fast a cruise ship can go. In fact, there are several ways to answer this question. Cruise ships can move surprisingly fast, but they usually don’t move as fast as they can.

A brief history of cruise ships and how fast they could go

Cruise ship | Getty Images

As CruiseNation explains, the first ship that would be defined as a cruise ship today was an ocean liner hired to deliver mail. Founded by sailors Brodie McGhie, Arthur Anderson and Captain Richard Bourne, the Peninsular & Oriental Steam Navigation Company secured the post of delivering mail from England to Egypt in 1840. It was so successful that the P&O was incorporated in the Royal Charter.

Four years later, in 1844, the P&O began advertising its steamboat service to paying passengers who embarked at Southampton and traveled in style to Gibraltar, Malta and Alexandria. Steamships of this era were able to travel on water at speeds between 11.25 and 14 knots per hour, explains GG Archives.

Today’s modern cruise ships can travel much faster — an average of 18 to 22 knots — but typically won’t reach top speeds without a compelling reason to, CruiseHive says.

The fastest and slowest cruise ships in the world

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Although 21st century cruise ships are bigger and heavier than their ocean-going predecessors, they tend to move more slowly for a number of reasons. One of those reasons is fuel economy, says Royal Caribbean whose fastest cruise ship, Harmony of the Seas, can reach speeds of 25 knots, but rarely does. Why? As with land transport, the faster the speed, the higher the fuel consumption.

Other factors also determine the speed of cruise ships, says Cruise Mummy. When the itinerary reveals a long time to the next port of call, cruise ships go slower. Cruise ships also tend to slow down as they approach ports and may even drop anchor at sea if it looks like the boat will arrive too soon. In areas like Alaska, cruise ship captains typically go slower to avoid navigational hazards such as icebergs.

Weather can also affect the speed of cruise ships. In rough or choppy seas, ships slow down to ensure passenger comfort. As a storm approaches, a cruise ship may accelerate away from its course.

The difference between mph and knots

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On land, speed is measured in miles per hour, or mpg. On water and in the air, speed is measured in knots. The reason is fascinating.

Sailors of old measured their speed by throwing a floating object over the bow of their ship, then counting the time it took before the stern caught up with the object. Known as the “Dutch log”, this method of measuring speed typically used a piece of wood. In the late 1700s, sailors devised and used a wedge-shaped, lead-weighted “chipping log” for the same purpose. With its attached spool of rope tied at even intervals, particleboard was the world’s first tool for navigation, says Bright Hub Engineering.

The sailor’s agglomerate required the deployment of two people – one to grab the rope spool and another to throw the tool. An hourglass was used to measure the time it took for the boat to sail away from the chip loch. This old measuring tool only offered an approximation of speed, but it gave us the term “knots” which is still used to measure ship speed today.

Converting knots to miles per hour is easy if you understand the formula. A knot is the rough equivalent of about 1.15 miles, so multiplying knots by 1.15077945 will tell you how fast a vessel is traveling in mpg, says Boat Safe.

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