It is remarkably difficult to grasp how large ships can be. I remember, many years ago, being amazed how a full sized city bus, which looked so large on the pier, seemed to shrink dramatically as it was hoisted and lowered into the hold of a ship.  The ship was not particularly large by today’s standards, yet the bus seem so small as it disappeared into the hold.  This memory was triggered by the recent publicity photo of the captain of the Queen Mary 2 standing on the ship’s bulbous bow.  Depending on the scale of the photo, Captain Kevin Oprey is barely visible with the bow of the ship towering over him.

But how does one even properly compare the sizes of different types of ships?  Tankers and dry bulk carriers are measured in terms of deadweight tons.  Cruise ships are measured in Gross Tonnage, which is the internal volume of the ship, or alternatively by the number of passengers and crew aboard. Container ships are sized by the number of TEU (Twenty-foot Equivalent Units), while LNG ships are judged by the number of cubic meters of LNG carried. And, on it goes.

The least accurate but most convenient way to compare different ship types is simply by length.  It does have the advantage that it is easy to visually compare different ships, assuming that they are all drawn to scale.

The Queen Mary 2 was the largest cruise ship when it was delivered, but is now roughly 15 meters shorter than the Allure of the Seas, which can accommodate around 8,000 passengers and crew.  The Vale Brasil is among the largest ore carriers ever built, with a capacity approaching 400,000 deadweight tons.  The largest container ships now sailing are the Mærsk “Triple E” class, which can each carry 18,270 TEU.  The Mærsk Mc-Kinney Møller was the first of the class to enter service.

The largest ship ever built was the Seawise Giant, later Happy Giant, Jahre Viking, and Knock Nevis.  At over a half million deadweigth tons, she was classed as a ULCC, an Ultra Large Crude Carrier.  The ship was scrapped in 2010.

While the Seawise Giant holds the record as the largest ship ever built, the largest vessel ever constructed will be the Prelude FLNG, a floating liquefied natural gas facility, for Royal Dutch Shell, currently under construction at Samsung Heavy Industries in Korea. The floating facility was launched in 2013 and is expected to go into service off Australia in 2017.  The Prelude FLNG is 488 metres (1,601 ft) long, 74 metres (243 ft) wide, and will have a displacement of more than 600,000 tonnes in service.

Will larger ships be built, or have we reached the practical upper limits? The Seawise Giant was so large that the she could not navigate the English Channel, the Suez Canal or the Panama Canal.  Only four other and smaller ULCCs have been built in the last 30 years.  The Mærsk Mc-Kinney Møller is thought to be about the largest container ship capable of transiting the Strait of Malacca and is too large for the Panama Canal. We may yet see larger ships. On the other hand, the old Norwegian expression comes to mind — trees do not grow to the sky.

To find a ship larger than the Seawise Giant or the Prelude FLNG, one needs to look to fiction. Apparently, only the later versions of Star Trek’s Starship Enterprise are notionally bigger than the Seawise Giant/Knock Nevis.