Floating LNG projects are accelerating at record pace, with today’s estimated 16 million tonnes of liquefaction capacity forecast to climb to 42 million tonnes by 2030 and to 55 million tonnes by 2040, according to Oslo-based Rystad energy.

At end-2025, eight FLNG facilities were in production with another nine projects under construction, adding more than 20 million tonnes of capacity in countries including Cameroon, Republic of Congo, Mauritania, Mozambique, and Senegal.

Floating projects are facilitating access to large volumes of LNG that would otherwise stay locked under land and sea.

Although early projects such as Shell’s Prelude, a newbuild in western Australia, were subject to lengthy delays and cost overruns, the sector has overcome many challenges in a short space of time. And floating projects, which may involve converted or purpose-built vessels, have many advantages.

They are faster and cheaper to develop compared with land-based facilities. They are more flexible, safer, and can be deployed in remote regions where shore-based plant would prove too expensive or risky.

But they do come with some design challenges, one of which is space. Shore-based plants can be spread out across land. Floating systems based on conversions, however, must accommodate all of the complex cryogenic plant, engineering and control systems within a ship’s hull. The only practical way is to build vertically, with large and heavy engineering plant above deck.

This, in turn, generates both stability and motion control issues. High centres of gravity result in lower metacentric heights which, if they turn negative, risk a loss of stability and ultimately capsize.

A ship’s metacentre is dependent, in part, on its beam, so Shell’s purpose-built Prelude unit, for example, has a beam of 74m and a length of 488m, giving a L:B ratio of 6.59. This corresponds with a typical LNG carrier.

Motion control is essential because side-by-side cargo operations can generate synchronous rolling. This in turn generates the risk of structural damage if vessels collide or even, at worst, the risk of capsize.

Ship motion control is also essential to limit cargo sloshing, particularly if cryogenic tanks are only partially loaded. This can cause high pressures on tank walls, damage to insulation systems, and higher boil-off rates. As an aside, the design of Moss-type tanks prevents cargo sloshing.

An FLNG plant is designed to remain on station for long periods of time which, depending on reservoir size, could be up to 20 years. This means, unlike ships, that all the operational features, components, cargo tank infrastructure, and engineering systems should be capable of outlasting the deployment. 

There are far-ranging implications for every aspect of design and build. But one of the most important is weather-proofing. Assets must be designed to handle both primary motions – roll, pitch and yaw – but also the related accelerated motions – surge, sway and heave. And, in many projects, they must be capable of safely withstanding the most violent ocean conditions.

In exposed locations, floating assets are often designed to ‘weathervane’ by using turret moorings from which they can disconnect. In severe weather, they face in the direction of least resistance to wind and waves, and, in extreme weather, they must be able to decouple completely and sail out of harm’s way under their own power.

In the event of internal damage, systems are required to prevent shock to non-cryogenic materials in the event of a cargo leak. LNG must be prevented from impact with ships’ steel hulls at all costs, as this can lead to brittle fracture and potentially catastrophic structural failure.

Coatings – internal and external – are another key design feature. Above the waterline, hulls are exposed to salty environments for long periods and sea spray is a catalyst for rapid corrosion. Below the waterline, the hull and sub-surface components are prone to marine organism attachment that potentially add weight.

Decisions on whether a newbuild or conversion is most appropriate will depend on a particular project, but projects can be dramatically different.

As FLNG technology adoption accelerates, however, the body of knowledge is growing exponentially. Shell’s Prelude project was built in South Korea by a Technip-Samsung consortium. Project costs soon exceeded predictions by vast margins.

Since then, analysts estimate that developments involving newbuilds may have reduced by up to 50% in terms of overall liquefaction costs per tonne of LNG. Conversions are significantly less again.

There are plenty of projects in the pipeline and there are also many uncompetitive LNG steamers with Moss-type tanks available as conversion candidates. But each project will need the hand of a highly skilled naval architect.