Everything else in the LNG chain assumes a jetty. Ship-to-ship transfer is what happens when there is not one, or when the vessel that can reach the cargo is not the vessel that should carry it across an ocean.
Why it exists
Transshipment. Ice-class carriers are expensive, heavily built and slow in open water. Using one for an eight-thousand-mile ocean voyage wastes it. So the ice-class ship shuttles out of the Arctic to an ice-free transfer point, hands the cargo to a conventional carrier, and turns around.
Floating storage. A moored storage vessel has to be filled by something, and that something is a carrier alongside.
Breaking bulk. A full cargo arriving at a hub can be redistributed in parcels to markets too small or too shallow for a conventional ship, by small-scale vessels that load ship-to-ship.
Bunkering. Supplying LNG as fuel to a gas-burning ship is a ship-to-ship transfer, just a small one.
How it is done
Two vessels moor alongside each other, either at anchor, at a dedicated mooring, or under way at slow speed. Large pneumatic fenders hold them apart and absorb the relative movement. Mooring lines are run in a pattern planned in advance for the specific pair of ships.
Cargo hoses or hard arms connect the manifolds. The two emergency shutdown systems are linked, so either vessel can stop the transfer and close valves on both sides. Then the pumps run, and the cargo moves.
The operation is governed by established industry guidance rather than improvised, with a compatibility study completed before the ships ever meet, a joint plan agreed between the two masters, and a person in overall advisory charge of the transfer.
What actually constrains it
Not the cargo. LNG transfer between ships is the same physics as transfer to a jetty, and the equipment is comparable.
Weather is the constraint. Two large vessels moored together in open water move independently in wind and swell, working the fenders and the mooring lines. Limits on wind speed, wave height and relative motion are set in advance and enforced, and operations stop as conditions approach them rather than when they exceed them. A transshipment point is chosen for shelter as much as for geography.
Compatibility is the other. Manifold height above the waterline changes as a ship loads or discharges, and two vessels at different drafts may not present their connections at compatible heights. Manifold spacing, fender arrangement, mooring fittings and shutdown systems all have to match. The ship–shore interface problem is the same problem, with a second ship instead of a jetty.
Floating storage as an asset class
A floating storage unit is usually an older carrier whose engines are no longer worth running but whose tanks are perfectly good. Moored permanently, it provides buffer volume wherever land is unavailable, expensive or slow to permit.
Paired with regasification the same vessel becomes an FSRU, which is the arrangement that let several countries add import capacity in about a year. Without regasification it is storage feeding something else — a small onshore plant, a distribution fleet, or a power station.
This is why free-standing containment keeps a niche. A storage vessel’s tanks rise and fall constantly and sit at partial levels for long periods, which is the condition membrane systems historically restricted.
What the tracker records
Terminals, including floating ones, appear in the data with their capacity and status. Transfer operations do not: this site holds no vessel movements, no cargo records and no positions, and nothing here should be read as tracking.
Where transshipment matters for reading the data is in what a terminal’s throughput means. A cargo that passes through a floating storage unit and is redistributed has crossed more than one facility, and counting capacity at each without noticing would double it.