Vessel Technology
Moss vs Membrane LNG Carriers: Understanding Cargo Containment Systems
How spherical and membrane containment differ in structure, hull-space use, filling-level behaviour and trade suitability.
Why containment choice matters
Containment selection sits at the intersection of vessel design, cargo integrity and commercial performance. It decides how much cargo fits in a hull, how the ship behaves at partial filling, and which terminals and trades suit the vessel.
This explainer covers principles rather than vessel-specific guidance. Figures quoted anywhere on OSSA LNG are indicative and vary by design, generation, shipyard and operator.
Two structural philosophies
A Moss tank is self-supporting: the sphere carries its own cargo loads and passes them to the hull through an equatorial skirt. The containment boundary is a distinct structure that can be inspected as such.
A membrane tank works the other way round. A thin primary barrier holds the cargo, and the insulation transfers the load into the inner hull. The insulation is structural as well as thermal.
Hull-space use and filling levels
Membrane tanks follow the hull form, so they generally use the available envelope efficiently. Spheres leave volume unused between the tank and the hull.
Self-supporting designs are generally tolerant of partial filling, which suits trades with frequent part-cargo operation. For membrane vessels, filling-level and sloshing guidance is project-specific and set out in the vessel's own documentation.
Where SPB fits
SPB prismatic tanks sit between the two concepts. They are self-supporting like Moss tanks but prismatic like membrane tanks, with internal swash bulkheads limiting cargo movement.
The flat tank top also leaves usable deck area, which is why the concept appears on floating infrastructure projects.
How to compare responsibly
No containment system is universally better. The right question is which system suits a given trade, terminal set, voyage length and operating profile.
Use the OSSA LNG comparison tool to place systems side by side across role, containment, capacity class, propulsion and boil-off handling, without artificial scoring.
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- Status
- Educational overview — editorial review required
- Seeded educational summary awaiting editorial and technical review.
- Last reviewed
- 15 September 2026
- Source status
- Sources pending editorial review.
Technical parameters are indicative and may vary by vessel design, generation, shipyard, operator and intended service.