Ship-to-Ship Transfer
A Ship-to-Ship Transfer (STS) is the transfer of a liquid or bulk cargo directly from one ship to another while they lie alongside each other, usually at anchor or drifting in a sheltered area, rather than at a shore terminal. It is common in the oil, gas and dry-bulk trades — for example to lighter a large tanker so it can enter a shallow port, or to break bulk a large cargo.
STS operations use large pneumatic fenders between the ships, moor them together, and transfer cargo by hose. They are governed by industry guidance and, for oil, by MARPOL, with an STS operation plan, weather limits and a designated person in overall control, because two large ships in contact transferring cargo is a high-risk operation.
STS transfer lets cargoes move where port depth or logistics would otherwise prevent it — lightering deep-draught tankers, breaking bulk, or transferring where no terminal exists. But it puts two large ships in physical contact while handling hazardous cargo, so it is one of the most carefully planned and risk-managed operations at sea.
Why are ship-to-ship transfers carried out?
To move cargo without a shore terminal — for example to lighter (partly discharge) a large tanker so it can enter a shallow port, to break a large bulk cargo into smaller parcels, or to transfer where no suitable terminal exists.