Largest LNG carriers sized for Qatar

Q-Max tankers are 1,132 feet by 177 feet, while most of the fleet is smaller and sized to fit most LNG export, import terminals

Stan Jones

Researcher/writer for the Office of the Federal Coordinator

How big are LNG tankers?

The world’s largest LNG carriers are the Q-Max tankers, so-called because they are the maximum size that can be accommodated at liquefaction terminals in Qatar, the world’s biggest exporter of LNG.

Q-Maxes are 1,132 feet long and 177 feet wide. They draw 39 feet of water. Qatar went for economies of scale with these ships - move the most gas in the biggest tanker possible - though only a limited number of customers can receive the big ships at their docks.

How big is a Q-Max? Pretty big, but not on the same scale as some of the world’s true seagoing behemoths.

The biggest ship ever - more of a barge than a ship, actually - is Shell’s gigantic Prelude floating LNG vessel. It was moved out of a South Korea dry dock in early December 2013 and is expected to enter service in an offshore Australia gas field in 2016. It’s 1,601 feet long - longer than five football fields - and has no propulsion of its own. Instead, it’ll be towed into position and anchored over the gas field. There, it will take gas piped from under the seabed, liquefy it and store it to be loaded on LNG tankers for shipment.

Probably the smallest oceangoing LNG tanker ever to sail was also the first: The Methane Pioneer, a mere 339 feet long. It left the U.S. Gulf Coast for England with the first load of LNG ever to cross an ocean in January 1959.

After Prelude, the big-ship field drops away pretty fast. Next are a fleet of Maersk Line container vessels at just over 1,300 feet, followed by a number of oil tankers over 1,200 feet, then the Q-Max tankers and some bulk carriers and cruise ships over 1,100 feet.

But what matters about a ship is not how long it is. The question is, how much cargo can it handle?

A Q-Max tanker can carry about 266,000 cubic meters of LNG, equal to roughly 5.5 billion cubic feet of natural gas in the vapor form burned in furnaces, water heaters and kitchen ranges. That’s enough to supply almost 75,000 U.S. households for a year. (The old Methane Pioneer carried 1/50th as much, about 5,000 cubic meters. The Polar Alaska and Arctic Tokyo, which launched the Alaska LNG trade, carried 71,500 cubic meters each.)

But most LNG carriers are not sized for the Qatar trade. They tend to be of a more utilitarian size - around 950 feet - so they can fit most LNG export and import terminals anywhere in the world. Their LNG capacity falls into the range from 125,000 to 175,000 cubic meters. Energy consultants IHS CERA reported that, as of late 2013, of the more than 100 new LNG tankers on order through 2017, only one had a capacity over 190,000 cubic meters.

The common mid-range tankers can move from 2.6 billion to 3.6 billion cubic feet of natural gas (when supercooled into LNG) per load, and the vessels envisioned for the proposed Alaska LNG project would fall within that range. The North Slope producer-led project would pipe natural gas from Prudhoe Bay and other North Slope fields to a liquefaction plant in Nikiski on the Kenai Peninsula. That project in full operation could fill several tankers per week.

LNG tankers and oil tankers are in essentially the same business - moving liquid energy across oceans. But, as a general rule, LNG costs more to get to market.

This is partly a function of two cost factors tied to producing and moving LNG.

One factor is the expense of the huge and complex plant that turns vapor into LNG. Another factor is that LNG tankers are more complicated to build and operate than oil tankers. The tanks holding the LNG must be heavily insulated to keep it cold enough to stay liquid, and the ship has to have onboard systems for managing what is called boil-off - the LNG that evaporates because no insulation system is perfect.

But another key factor at work in the higher cost of transporting LNG has nothing to do with equipment or operations. Rather, it’s basic physics: A given volume of LNG contains only about 64 percent as much energy as the same volume of crude oil.

For example, the crude oil on a fully loaded million-barrel tanker contains 5.6 trillion Btu of energy.

And LNG? A tanker of the same volume would carry 3.6 trillion Btu.

To put it another way, to move equal amounts of energy, you’d need either an LNG tanker about half again as big as your oil tanker, or 50 percent more tanker loads.

Floating thermos bottles

To keep the gas cold, LNG tankers come predominantly in two designs: Moss and membrane.

If there’s such a thing as an instantly recognizable LNG tanker, it’s one with the Moss design, developed by Norway’s Moss Maritime. What makes it recognizable is a row of what look like giant golf balls running down the middle of the deck. Those golf balls - typically about 140 feet across, or as wide as eight Chevy Suburbans parked bumper to bumper - are actually a series of spherical tanks for the LNG.

Moss tankers may be the most recognizable, but they are not the most common.

Instead, membrane tankers dominate the market. These look about like any other ocean freighter that doesn’t carry containerized cargo on deck. The bridge, several stories high, is at the back, and the deck is characterized by a complicated system of pipes and valves for getting LNG on and off the ship.

As of 2011, only about 30 percent of the world fleet relied on the Moss design and only about 6 percent of new orders were for Moss tankers, according to a report from the University of Texas Center for Energy Economics. The rest of the market belongs to membrane tankers.

Pros and cons

Moss tankers can be faster to build, because the spherical tanks are constructed separately from the ship, then lowered into position and installed when the vessel is ready. Also, Moss tankers don’t suffer from the problem of cargo sloshing described below.

On the other hand, those big tanks are heavy - typically around 900 tons each - meaning they can be built and installed in only a relative handful of shipyards.

Also on the downside, the shape of Moss tanks makes them a poor fit with a ship’s hull - they’ve been described as “balls in a box.” A membrane tanker, by contrast, has built-in tanks. They can be fitted to the shape of the hull and do not project far above the deck - a much more efficient use of space. As a result, it takes a bigger ship to haul the same amount of LNG in Moss tanks than in membrane tanks.

Since tolls and other ship fees are based on something called net tonnage - derived solely from ship’s dimensions without reference to its cargo capacity or the actual load aboard - Moss tankers pay more per cubic meter of LNG in tolls and fees. For example, a 2005 calculation by Lloyd’s Register determined that a Moss tanker able to carry 135,000 cubic meters of LNG would pay 30 percent more in net-tonnage-based fees to use the Suez Canal than a membrane tanker of the same capacity.

Further complicating the picture for Moss tankers is the fact that they are more subject to wind forces than membrane tankers and thus may bear the added expense of more escort tugs and pilots.

The chief advantage of the membrane tanker is its lower operating cost, for the reasons discussed above.

Editor’s note: Part 1 of this story appeared in the June 8 issue. Part 3 of this story will appear in the June 22 issue. This is a reprint from the Office of the Federal Coordinator, Alaska Natural Gas Transportation Projects, available online at www.arcticgas.gov/lng-carriers-called-floating-pipelines.