Ship-to-ship cargo transfer
A ship-to-ship (STS) transfer operation is the transfer of cargo between seagoing ships positioned alongside each other, either while stationary or underway. Cargoes typically transferred via STS methods include crude oil, liquefied gas (LPG or LNG), bulk cargo, and petroleum products. The nomenclature STS transfer should be used in reference to techniques used by civilian merchant vessels, as differentiated from underway replenishment which is the term used by the US Navy for similar, but usually far more complicated, operations between naval vessels while underway.
Most of cargo operations take place between a ship and a land-based terminal. Nevertheless it sometimes can be useful to transfer cargo from one ship to another in the open sea and this is called a ship-to-ship operation. One vessell will act as the terminal whilst the other one will moor. The receiving ship is called the mother vessel.
Reasons for
- Lightening a vessel prior to harbour entering or for re-floating
- Bunkering operations
- Earning time in a very tight schedule
Problems
It is not easy to close two moving objects smoothly. Therefore seafarers established a few procedures which will be used regarding the sizes and manoeuvrability's of the vessels involved. We can consider three configurations
- Vessels making way, fast approach (1)
- Mother vessel stopped (2)
- Vessels making way, tactful approach (3)
The table below show the required manoeuvre regarding the operation for a few vessels
| Pilot Boat | Supply Vessel | Bunker Barge | Open-sea vessel | |
|---|---|---|---|---|
| Pilot Boat | 3 | 1 | 1 | 1 |
| Supply Vessel | 1 | 3 | 3 | 3 |
| Bunker Barge | 1 | 3 | 2 | 2 |
| Open-sea Vessel | 1 | 3 | 2 | 3 |
Vessels making way, fast approach
Mother vessel stopped
When the manoeuvrability of the berthing vessel is not really high it is often less dangerous for her to approach a vessel stopped in the water. Like that there will be a protected side from the waves and the wind and there will also not be any bow wave. At that moment the vessel approaches on the quarter of the mother ship and get on a parallel heading at slow speed.In that case an artificial type wave can be created which can prevent the ship from stopping.
Vessels making way, tactful approach
It is of huge importance to maintain the heading of the “terminal” and this is not possible with stopped vessels. That's why we will not consider a static reference system but one in translation because a ship needs some speed to maintain her heading. The biggest vessel will act has a terminal heading on a steady course at manoeuvring speed. Then the second ship will come closer in the same direction but a bit faster. When the vessels are navigating side to side, they can be moored. First of all, the spring lines will be tensioned to maintain the vessels at the same speed. Then the breast lines will keep the vessels as close as possible. It is also possible to add head and stern lines to prevent any longitudinal motion.
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Vessels on a same course prior closing and exchanging lines
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First step of the mooring operation, securing the fore spring
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Passing the connecting hose prior cargo operation
Regulations
These operations are carried out in accordance with guidelines set out by the Oil Companies International Marine Forum and the International Chamber of Shipping (ICS), with the strictest adherence to safety regulations.
According to International Maritime Organization regulations vessels transferring OIL CARGO must have an approved STS operational manual that describes the procedure.[1] These manuals should be available on board not later than first annual, intermediate or special survey after 1 January 2011. These manuals can be prepared either by the shipping company or external consultants.[2]
References
- ↑ "RESOLUTION MEPC.186(59)". AMENDMENTS TO THE ANNEX OF THE PROTOCOL OF 1978 RELATING TO THE INTERNATIONAL CONVENTION FOR THE PREVENTION OF POLLUTION FROM SHIPS, 1973. 17 July 2009. Retrieved 18 August 2011.
- ↑ ANCO Maritime Activities Ltd (05/12/2010). "Ship To Ship oil transfer (STS) operation plans for oil tankers". ancomaritime.com. Retrieved 18 August 2011.