Moss / Spherical Type B Containment

What it is

• A self-supporting Type B containment concept in which each cargo tank is a sphere that carries its own structural loads.
• Each sphere is connected to the hull through an equatorial skirt, so cargo loads are transferred at a single defined interface.

Where it is used

• Ocean-going LNG carriers, particularly designs built for trades with frequent part-cargo operation.
• A number of floating storage and conversion projects that reuse existing spherical-tank hulls.

Key design characteristics

• Independent tanks with leak-before-failure design philosophy and defined inspection access.
• Insulation applied to the outer sphere surface rather than to the hull structure.
• Filling-level flexibility, which reduces sloshing-related operational restrictions.

Benefits

• Partial filling is generally routine, which suits part-cargo and multi-port operation.
• Structural separation between cargo tank and hull simplifies monitoring of the containment boundary.

Operational considerations

• Spherical geometry generally uses hull volume less efficiently than hull-conforming membrane tanks.
• A large above-deck profile affects visibility lines and wind-exposed area.

Related vessel segments

• Moss
• FSU
• Conversion FSRU

Related glossary terms

• Moss Tank
• Type B Tank
• Cargo Containment System
• Boil-off Gas