A gas carrier is a ship built to move a cargo that is a gas at ambient conditions and only stays liquid because it is cold, under pressure, or both. That single physical fact drives every design choice on the ship: the tank shape, the steel grade, the insulation, the reliquefaction plant, and the size the hull can grow to. The fleet splits first by cargo. Liquefied petroleum gas (LPG) carriers move propane, butane, ammonia, and petrochemical gases that liquefy with modest cooling or pressure. Liquefied natural gas (LNG) carriers move methane, which only turns liquid at about -163 C at atmospheric pressure and so needs true cryogenic containment. Both fleets are governed by one rulebook, the IMO International Code for the Construction and Equipment of Ships Carrying Liquefied Gases in Bulk, the IGC Code, mandatory under SOLAS Chapter VII for gas carriers built on or after 1 July 1986.
This article is the cluster hub for gas-carrier types. It walks the LPG classes by capacity in cubic metres, from small pressurised ships up to the Very Large Gas Carrier (VLGC) and the Very Large Ethane Carrier (VLEC), then the LNG classes from small-scale through the conventional band to the Qatari Q-Flex and Q-Max giants. It covers the three LPG cargo-containment regimes (fully pressurised, semi-refrigerated, fully refrigerated), the IGC tank-type framework that underpins them, and the two LNG containment families, membrane and Moss spherical, that define how an LNG ship is built. The companion tools are the LNG carrier CII calculator and the LPG and gas-carrier CII calculator, which apply the carbon-intensity reference lines that now sit on top of all this hardware.
The IGC Code and the three cargo regimes
The IGC Code is the spine of the whole gas fleet. It was adopted by IMO resolution MSC.5(48) and has been mandatory under SOLAS Chapter VII since 1 July 1986, with the amended Code (resolution MSC.370(93)) entering into force on 1 January 2016 and applying to gas carriers whose keels were laid on or after 1 July 2016. The Code sets the construction, equipment, and operating standard for any ship carrying a listed liquefied gas in bulk, and compliance is proven by the International Certificate of Fitness carried onboard. No certificate, no cargo. The Code’s central engineering idea is that the colder and more hazardous the cargo, the heavier the containment and the more redundancy the ship must carry, and it expresses that through tank types and secondary-barrier rules.
LPG ships are described by how they keep the cargo liquid, and there are three regimes. A fully pressurised carrier holds the cargo at ambient temperature under pressure alone. Propane has a vapor pressure of roughly 17 to 18 bar at 45 C, so a fully pressurised ship uses thick-walled cylindrical or spherical pressure vessels rated to about that level and carries no cooling plant at all. These are the simplest gas ships to build because they have no temperature-control equipment; the trade-off is that the heavy pressure vessels are expensive per cubic metre and limit the ship to small parcels over short distances. They dominate the smallest end of the fleet, the coastal and short-sea LPG trades.
A semi-refrigerated carrier splits the difference. It carries cargo at a moderate pressure (typically a few bar) and a moderate cold (down to roughly -48 C for LPG grades), using Type C independent pressure-vessel tanks plus a reliquefaction plant that recondenses boil-off and holds the tank conditions. Because the tank is a Type C pressure vessel, the IGC Code does not require a full secondary barrier, which keeps construction simpler than a fully refrigerated ship while letting the vessel load from either a pressurised or a refrigerated terminal. Semi-refrigerated ships are the flexible workhorses of the smaller and mid-size LPG and petrochemical trades, and many ethylene carriers sit here with tanks rated down to about -104 C.
A fully refrigerated carrier carries cargo at or near atmospheric pressure and at the cargo’s atmospheric boiling point, propane at about -42 C and butane at about -0.5 C, in large prismatic Type A independent tanks. Atmospheric pressure means the tank walls can be thin, so a fully refrigerated ship gets far more cargo into a given hull than a pressurised one, which is why every large LPG ship is fully refrigerated. The cost is a secondary barrier: Type A tanks carrying cargo below -10 C require a complete secondary barrier under the IGC Code, because a leak of cold liquid would embrittle ordinary hull steel. That secondary-barrier requirement is the dividing line that makes the big refrigerated ships more complex to build than the semi-refrigerated mid-size fleet.
IGC tank types A, B, and C
The tank-type taxonomy is worth getting exactly right because it explains the secondary-barrier rules. A Type A tank is a self-supporting prismatic tank designed by classical ship-structural methods; below -10 C it needs a full secondary barrier, and it is the standard for fully refrigerated LPG and ammonia ships. A Type B tank is designed with detailed fatigue and crack-propagation analysis, so the Code accepts a partial secondary barrier; the Moss sphere is the archetypal Type B tank. A Type C tank is a pressure vessel designed to recognized pressure-vessel codes; its inherent strength means no secondary barrier is required, and it is the standard for fully pressurised and semi-refrigerated ships. Membrane tanks are a separate category: a thin non-self-supporting membrane backed by insulation, with the full secondary barrier built into the insulation system, used almost exclusively for LNG.
LPG carrier classes by capacity
The LPG fleet is conventionally split into capacity bands, and although the exact boundaries vary between brokers and registries, the classes below are the ones the trade actually uses. Capacity is quoted in cubic metres of cargo, not deadweight, because the limiting factor for a gas ship is tank volume.
Small and pressurised carriers
At the bottom sit the small pressurised carriers, from a few hundred cubic metres up to roughly 5,000 cbm, and small semi-refrigerated ships up to around 7,500 cbm. These ships serve coastal distribution, island supply, and short petrochemical hauls where parcels are small and many ports are too shallow or too small for a big ship. The pressurised ones carry no cooling plant; the semi-refrigerated ones carry a small reliquefaction unit. They load grades that a larger refrigerated ship cannot economically serve, including pressurised LPG, propylene, and small ammonia parcels. Their economics turn on parcel flexibility rather than scale: a fully pressurised 3,500 cbm ship can carry several grades in separate tanks and discharge at a terminal that has no refrigerated handling at all.
Handysize and Midsize Gas Carrier (MGC)
Above the small ships the handysize gas carrier covers roughly the 12,000 to 22,000 cbm range, often semi-refrigerated and used for both LPG and petrochemicals such as ethylene and propylene. The Midsize Gas Carrier (MGC) sits next, conventionally about 20,000 to 43,000 cbm, fully refrigerated for LPG and ammonia work. The MGC is the bridge between the regional ships and the big intercontinental carriers. Its size lets it reach ports that cannot take a VLGC while still moving a cargo large enough for a transoceanic voyage, and the fully refrigerated tank set makes it efficient on propane and butane. Ammonia is a major MGC cargo because the fertilizer trade moves parcels that suit this size, and the same ships are now central to the emerging low-carbon ammonia discussion.
Large Gas Carrier (LGC) and Very Large Gas Carrier (VLGC)
The Large Gas Carrier (LGC) covers roughly 45,000 to 60,000 cbm, fully refrigerated, a class that was once the backbone of long-haul LPG before the VLGC took over. Above it sits the Very Large Gas Carrier, the workhorse of the modern propane and butane trade. A VLGC carries roughly 80,000 to 84,000 cbm of fully refrigerated LPG, with propane at about -42 C and butane near its atmospheric boiling point, in prismatic Type A tanks with full secondary barriers. The standard newbuilding has settled around 84,000 cbm because that hull envelope, beam and length together, is shaped to fit the expanded Panama Canal. The Neopanamax locks that opened in June 2016 let an 84,000 cbm VLGC carry US Gulf Coast propane straight to Asian buyers in Japan, South Korea, and China without the long detour around Cape Horn.
The VLGC is where LPG shipping reaches industrial scale. The US shale boom turned the US Gulf Coast into the world’s swing LPG exporter, and the Middle East Gulf remains the other great load region, so the VLGC trade is built on two long legs into Asia. Owners such as BW LPG operate VLGC fleets of around fifty ships, an increasing share of them fitted with LPG dual-fuel engines that burn part of the cargo as fuel. The class is sensitive to the Panama Canal in a way no other gas ship is: when canal draught was restricted during the 2023 to 2024 drought, transit slots tightened and some VLGCs rerouted around Cape Horn, which lengthened voyages, tied up tonnage, and lifted freight. The LPG and gas-carrier CII calculator applies the MEPC.337 carbon-intensity reference line that splits at 65,000 DWT, which puts the VLGC on the larger-ship line.
Very Large Ethane Carrier (VLEC)
The newest LPG-family class is the Very Large Ethane Carrier (VLEC), built to move ethane, the feedstock that US shale crackers produce in surplus, to petrochemical plants in Asia and Europe. Ethane liquefies at about -89 C at atmospheric pressure and the operating cargo temperature on a VLEC runs near -104 C, between LPG and LNG, which makes containment the hard problem. Lloyd’s Register and other class societies treat the VLEC as a distinct design because the tanks must hold an intermediate cryogenic cargo and, on the larger ships, double as a route for ethane or a mix of ethane and LNG. The first VLECs were ordered in the mid-2010s for the trade out of the US Gulf, with cargo capacities in the 85,000 to 98,000 cbm range and tank technologies ranging from Type B and Type C arrangements to membrane systems on the largest units. The VLEC exists because ethane is too cold for a standard LPG ship and too valuable as a chemical feedstock to leave stranded at the wellhead.
LNG carrier classes by capacity
LNG carriers are a separate world because the cargo is so much colder. Methane stays liquid at atmospheric pressure only at about -163 C, so every LNG ship is a cryogenic vessel with heavy insulation, and the cargo is never simply pressurised at ambient temperature the way LPG can be. The fleet is graded by tank volume in cubic metres, and the classes below trace the history of the trade from regional ships to the Qatari giants.
Small-scale LNG carriers
Small-scale LNG carriers run from a few thousand cubic metres up to roughly 40,000 cbm. They feed the distribution layer of the LNG business: bunkering ships that refuel LNG-powered vessels, feeder ships that serve small import terminals, and ships supplying island and remote-coast power plants that a full-size carrier cannot reach. The class grew with LNG marine fuel and with the spread of small import terminals across Southeast Asia, the Caribbean, and the Baltic. Many small-scale ships use Type C pressure-vessel tanks, the same tank family as a semi-refrigerated LPG ship, because at small scale a pressure vessel that tolerates pressure build-up is simpler than a membrane tank and copes well with the frequent partial fills of a feeder or bunker operation.
Conventional LNG carriers
The conventional LNG carrier is the standard ocean-going ship of the LNG trade, and the modern band runs from about 125,000 to 180,000 cbm, with the dominant newbuilding size settling around 174,000 cbm. This is the ship that links the world’s liquefaction plants in Qatar, Australia, the US Gulf, and elsewhere to the regasification terminals in Asia and Europe. A conventional carrier of this size carries enough gas to supply a mid-size city for a meaningful period, and the 174,000 cbm standard exists because it is the largest ship that the great majority of LNG import and export terminals can berth on their existing jetties and water depth. Most conventional ships now use GTT membrane containment, though a substantial Moss-sphere fleet remains in service. The LNG carrier CII calculator applies the unique flat MEPC.337 LNG reference line that these ships are rated against.
Q-Flex and Q-Max: the Qatari giants
Above the conventional band sit the two largest LNG classes ever built, both developed for Qatar’s export program through Nakilat and its partners. A Q-Flex holds about 210,000 cubic metres of LNG and a Q-Max about 266,000 cubic metres, putting the Q-Max roughly 50% larger than a standard conventional ship. The naming is literal: the Q is for Qatar, and Flex and Max mark the two size steps, with Max the upper limit of what the program built. The Q-Max is the largest LNG carrier class in service. Nakilat’s fleet illustrates the scale, comprising Q-Max, Q-Flex, and conventional ships, with the Q-class vessels purpose-built to move Qatari gas to distant markets in single large parcels and so cut the per-unit shipping cost on the long hauls to Asia and Europe.
Both Q-classes use GTT membrane containment and, unlike most early conventional ships, carry onboard reliquefaction plant rather than burning all their boil-off, because at 210,000 to 266,000 cbm the absolute volume of daily boil-off is large enough that recondensing it and returning it to the tanks preserves cargo worth keeping. They were also among the first large LNG carriers propelled by slow-speed diesel engines rather than steam turbines, which lifted propulsive efficiency on the long Qatar-to-Asia and Qatar-to-Europe routes. A newer QC-Max generation, ordered in the 2020s and larger still, is now under construction in China, extending the line that Q-Flex and Q-Max began.
LNG containment systems: membrane vs Moss
Every conventional and large LNG carrier uses one of two containment families, and the choice shapes the whole ship. The split is between membrane tanks, supplied by GTT, and Moss spherical tanks, the self-supporting spheres developed by Moss Maritime (originally Moss Rosenberg and the Kvaerner group). The deeper treatment of insulation, secondary barriers, and sloshing lives in the dedicated article on LNG cargo containment systems; the summary here is enough to place each ship class.
GTT membrane systems: Mark III and NO96
A membrane system uses a thin metal membrane, only a fraction of a millimetre to a few millimetres thick, that holds the liquid but carries no structural load. The cargo weight passes through a load-bearing insulation layer into the ship’s inner hull, which is the actual structural tank. GTT (Gaztransport and Technigaz) supplies the two dominant membrane families. The NO96 system uses two thin Invar membranes, Invar being a nickel-steel alloy whose near-zero thermal expansion lets it tolerate the cool-down without buckling, with insulation boxes between and behind them. The Mark III system uses a corrugated stainless-steel primary membrane over reinforced polyurethane-foam insulation, with a secondary membrane laminated into the insulation. Both are cryogenic membrane solutions designed to hold LNG at atmospheric pressure and -163 C.
The membrane advantage is volumetric efficiency. Because the tank conforms to the prismatic shape of the hull rather than sitting as a sphere inside it, a membrane ship fits more cargo into a given length and beam, which is why the 174,000 cbm standard and the Q-Max are both membrane designs. The trade-off is that membrane tanks are sensitive to sloshing loads at partial fill: a half-full tank in a seaway can generate impact pressures that the thin membrane and its insulation must be engineered to survive, which historically constrained partial-fill operation and drove much of the fatigue and crushing-strength research on the Mark III and NO96 systems.
Moss spherical tanks
A Moss system uses self-supporting spherical tanks, typically four or five of them in a row, made of aluminium alloy or 9% nickel steel, each sitting in the hull on a cylindrical skirt. These are the visible domes that give the classic Moss LNG carrier its profile, the upper half of each sphere standing proud of the deck. A Moss tank is an IGC Type B independent tank, designed with the detailed crack-analysis that lets the Code accept a partial rather than a full secondary barrier; a drip tray and partial barrier under each sphere catch any leak. The sphere carries its own cargo load independent of the hull.
The Moss advantage is partial-fill freedom and inspection access. A self-supporting sphere handles partial fills without the sloshing-pressure constraint that limits membrane tanks, so a Moss ship can sail at any fill level, which suited the early trade and still suits ships that load and discharge part cargoes. The sphere is also fully accessible for inspection, inside and out. The trade-off is volumetric: spheres waste the space between the round tank and the square hull, so a Moss ship needs a longer or beamier hull than a membrane ship of the same capacity, and the domes raise air draught and windage. That space penalty is why the newbuilding market has moved heavily toward membrane, even though a large installed Moss fleet keeps running.
Why ethylene and ammonia sit between the regimes
Two cargoes complicate the LPG picture because they sit at temperatures the simple regime labels do not capture. Ethylene is normally carried fully refrigerated at its atmospheric boiling point of about -104 C, far colder than propane, so an ethylene carrier needs Type C pressure-vessel tanks built from 5% nickel steel that stay tough at that temperature, and no secondary barrier is required because the tank is Type C. That is why a dedicated ethylene carrier is a more specialized and costly ship than a plain LPG carrier of the same size, and why ethylene is a semi-refrigerated rather than a fully refrigerated trade in the conventional sense. The same cargo-flexibility logic carries ethylene ships up into the handysize and mid-size bands, where a single ship may load ethylene, propylene, or LPG on different voyages.
Ammonia is the other cargo that bends the categories. Anhydrous ammonia liquefies at about -33 C and is carried fully refrigerated in the same Type A prismatic tanks as LPG, so a fully refrigerated LPG carrier and an ammonia carrier are often the same hull. The fertilizer trade moves ammonia in mid-size parcels, which is why the MGC class is so central to it. Ammonia is also at the heart of the marine-fuel transition: the IMO has deleted the IGC Code prohibition on using a toxic cargo as fuel so that ammonia carriers can burn part of their own cargo, and class societies and SIGTTO are working through the safety case for ammonia as a bunker fuel. That puts the mid-size ammonia carrier at the center of a trade that may grow well beyond fertilizer.
Cargo temperatures, tank materials, and why steel grade matters
The steel grade is not a detail; it is the reason the classes exist at the capacities they do. Ordinary mild steel turns brittle when it gets cold, and a brittle hull next to a leak of cryogenic liquid is a fracture risk, so each cargo temperature forces a material choice that ripples through the whole design. A fully pressurised LPG ship carries cargo at ambient temperature, so its Type C pressure vessels can use ordinary carbon-manganese steel, which is cheap, and the only penalty is the wall thickness needed for pressure. That is why the pressurised ships are simple to build and small: thick carbon-steel pressure vessels are heavy and costly per cubic metre.
Drop the temperature and the steel changes. Fully refrigerated LPG at -42 C and ammonia at -33 C use low-temperature carbon steels or fine-grained steels qualified for that range in the large Type A prismatic tanks. Ethylene at -104 C needs 5% nickel steel, which holds its toughness far below the point where ordinary steel fails. LNG at -163 C needs the toughest cryogenic materials of all: 9% nickel steel or aluminium alloy for Moss spheres, and Invar (a 36% nickel-iron alloy) or stainless steel for the membrane systems. Invar earns its place in the NO96 system because its thermal contraction over the 188-degree cool-down from ambient to -163 C is near zero, so the thin membrane does not have to absorb large dimensional change. The colder the cargo, the more nickel in the steel, the more expensive the ship, and the stronger the case for building it large enough to spread that cost over a big cargo.
The secondary barrier follows the same logic from the other direction. The IGC Code requires a full secondary barrier where a leak of cold cargo could reach and damage the hull, which is why fully refrigerated Type A ships and membrane LNG ships carry one, while Type C ships (pressurised and semi-refrigerated) and Type B ships (Moss) carry a reduced barrier or none. The barrier is a second containment skin that holds the cargo for a defined period if the primary tank leaks, long enough to manage the cargo to safety. It is one of the most expensive parts of a refrigerated gas ship, and the desire to avoid a full secondary barrier is part of why the Type C pressure vessel remains attractive at the smaller end of both the LPG and small-scale LNG fleets.
Boil-off gas and reliquefaction
Boil-off gas is the unavoidable consequence of carrying a cryogenic liquid in an imperfectly insulated tank. Heat leaks in through the insulation and a small fraction of the cargo evaporates every day; the natural boil-off rate of a modern LNG carrier is a fraction of a percent of cargo volume per day. On a conventional ship the absolute quantity is still large. For a 174,000 cbm carrier, every 0.05% per day reduction in boil-off conserves on the order of 36 tonnes of LNG per day, which is why insulation quality and tank design carry hard economic value rather than being a comfort feature.
There are two ways to handle boil-off, and they split the fleet. The traditional approach burns the boil-off as fuel: early LNG carriers used steam turbines specifically because a boiler will happily burn methane vapor, and modern dual-fuel diesel engines do the same more efficiently. The alternative is reliquefaction: an onboard plant recompresses and recondenses the boil-off and returns it to the tanks as liquid, keeping the cargo intact. The Qatari Q-Flex and Q-Max ships pioneered large-scale onboard reliquefaction precisely because their cargoes were large and valuable enough that recovering the boil-off beat burning it. On LPG carriers reliquefaction is the norm for semi-refrigerated and fully refrigerated ships, and the plant’s efficiency is captured by its coefficient of performance, the subject of the LPG reliquefaction COP calculator. The LNG boil-off rate calculator and the LNG heel-return calculator work the cargo-side numbers that follow from the boil-off rate.
LNG propulsion and the steam-to-diesel shift
Propulsion is bound up with the cargo on an LNG carrier in a way it is not on most ships, because the cargo is also a fuel. For roughly four decades the standard LNG carrier ran a steam turbine, an arrangement that had largely disappeared from the rest of the merchant fleet. The reason was the boiler: a steam plant burns boil-off gas directly in dual-fuel boilers that raise steam to drive the turbine through reduction gearing, which neatly disposes of the gas a cryogenic cargo gives off whether the ship wants it or not. The penalty was efficiency. A marine steam plant runs at roughly 30 to 35% thermal efficiency, well below a modern diesel, so a steam LNG carrier burned more energy per tonne-mile than its cargo economics would have liked.
The shift away from steam came in stages. Dual-fuel diesel-electric (DFDE) plants put medium-speed dual-fuel engines on generators that feed electric propulsion motors, lifting efficiency while keeping the ability to burn boil-off. Then the slow-speed two-stroke dual-fuel engines arrived: the MAN ME-GI, a high-pressure gas-injection engine, and the WinGD X-DF, a low-pressure Otto-cycle engine, with the first slow-speed dual-fuel LNG carrier commissioned in 2016. These engines are the same family now driving LNG-fueled ships across the wider fleet, and on an LNG carrier they let the ship burn boil-off, burn fuel oil, or run on reliquefied cargo as the voyage economics dictate. The propulsion story therefore tracks the containment and reliquefaction story: a ship that can recondense its boil-off, like a Q-class carrier, needs an efficient engine to make recovery worthwhile, and the slow-speed dual-fuel engine is what made onboard reliquefaction pay.
The gas trades and where each class fits
The class structure only makes sense against the trades it serves. LPG moves on two great long-haul corridors into Asia, one from the US Gulf Coast and one from the Middle East Gulf, plus a web of shorter regional flows. The US shale boom turned the Gulf Coast into the swing exporter of propane and butane, and the VLGC is the ship that monetizes that gas by reaching Asian buyers on the short Panama route. The mid-size and handysize ships fill the gaps the VLGC cannot serve: smaller ports, smaller parcels, petrochemical grades, and the ammonia trade. The small pressurised and semi-refrigerated ships handle coastal distribution and the multi-grade parcels that need tank flexibility more than scale.
LNG moves on a different map. Liquefaction is concentrated at a handful of large plants in Qatar, Australia, the US Gulf, and a few other regions, and regasification is concentrated at import terminals in Japan, South Korea, China, and Europe. The conventional 174,000 cbm carrier is the ship that links any plant to any terminal, which is why it dominates the fleet: it is the largest ship the common terminal can take. The Q-class exists because Qatar’s volumes and dedicated corridors justified ships too large for the general terminal network, trading universal port access for the lowest cost per tonne on its specific routes. The small-scale ships sit underneath both, distributing LNG to bunkering operations and to terminals the conventional ship is too large to enter. The freight side of all this, including the LNG freight assessments, is covered in the article on the Baltic Dry Index and freight indices.
The defining constraints
Each class is shaped by one dominant constraint, and naming it is the fastest way to understand why the fleet looks the way it does.
The VLGC is sized by the Panama Canal. The 84,000 cbm standard is not an arbitrary optimum; it is the largest fully refrigerated LPG ship that fits the Neopanamax locks, which is what lets US Gulf propane reach Asia on the short route. Move the cargo any larger and the ship loses canal access and has to round Cape Horn, which is exactly what drought-driven draught restrictions in 2023 and 2024 forced on part of the fleet. The Panama Canal is therefore the single number that fixes VLGC dimensions.
The conventional LNG carrier is sized by terminal infrastructure. The 174,000 cbm standard exists because it is the largest ship that the bulk of the world’s liquefaction and regasification jetties can berth given their water depth, jetty length, and mooring layout. A ship that no terminal can receive carries no cargo, so the conventional band tracks the lowest common denominator of the global terminal network rather than the shipyard’s maximum buildable size.
The Q-Max is limited by water depth and draught at the terminals that can take it. At 266,000 cbm it can only call at ports dredged and equipped for it, which is why the Q-class was built for specific long-haul corridors out of Qatar rather than for the general spot trade. Its economy of scale only pays on routes where both ends have the depth, the jetty, and the cargo volume to fill a single 266,000 cbm parcel.
The membrane-versus-Moss choice is a trade between volume and partial-fill freedom. Membrane wins on cargo per metre of hull, which is why the largest and most numerous modern ships are membrane. Moss wins on sloshing tolerance and inspection access, which kept it competitive for decades and still serves a large installed fleet. The two systems answer the same problem, holding methane at -163 C, with opposite priorities, and a newbuilding owner picks the one that matches the intended trade.
Limitations
The capacity bands in this article are working categories, not legal definitions. Brokers, registries, and class societies draw the LGC, MGC, and VLGC boundaries at slightly different cubic-metre figures, and a ship near a boundary may be counted in either class depending on the source. The figures here, VLGC around 80,000 to 84,000 cbm, conventional LNG 125,000 to 180,000 cbm, Q-Flex about 210,000 cbm, Q-Max about 266,000 cbm, are the commonly cited values and match the Qatari program’s published descriptions, but a specific ship should be checked against its own registered cargo capacity rather than the band.
This is a classification overview, not a cargo-handling or stability manual. The IGC Code’s detailed requirements on tank materials, secondary-barrier extent, relief-valve sizing, gas-detection, and cargo compatibility are extensive and govern the actual ship; the tank-type summary here is a map, not the territory. Cargo temperatures quoted (propane -42 C, butane near 0 C, ethane around -104 C, LNG -163 C) are nominal atmospheric boiling points or typical carriage temperatures and vary with cargo grade, purity, and tank pressure.
The reliquefaction and boil-off figures are representative, not ship-specific. Actual boil-off depends on the insulation system, the age and condition of the tanks, sea and ambient temperature, voyage length, and fill level, and a real ship’s heat-balance must come from its own gas-trial and operating data. The carbon-intensity reference lines applied by the companion calculators follow the IMO MEPC.337 framework as it stands, and that framework is subject to ongoing IMO review, so a rating computed today reflects the current reduction factors rather than a permanent value.
See also
- LNG carrier: the LNG ship in detail, including propulsion, dual-fuel engines, and the LNG trade.
- LNG cargo containment systems: the full treatment of Moss spheres, GTT NO96 and Mark III membranes, SPB tanks, insulation, and sloshing.
- Baltic Dry Index and freight indices: how the gas, dry, and tanker freight benchmarks are built and how TCE turns them into dollars per day.
- LNG carrier CII calculator: carbon intensity for LNG carriers on the flat MEPC.337 LNG reference line.
- LPG and gas-carrier CII calculator: carbon intensity for LPG, ethylene, and ammonia carriers on the size-split MEPC.337 lines.