Ship-to-ship cargo transfer
Encyclopedia
A ship-to-ship 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.
Most of cargo operations are taking place between a ship and a land-based terminal. Nevertheless it sometime can be useful to transfer cargo from one ship to another in open sea and this is called a ship-to-ship operation. At that moment, one of them will act as the terminal where the other one will moor. The receiving ship is called the mother vessel.
We can consider three configurations
The table below show the required manoeuvre regarding the operation for a few vesselsPilot Boat
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.
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. 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.
Petroleum
Petroleum or crude oil is a naturally occurring, flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds, that are found in geologic formations beneath the Earth's surface. Petroleum is recovered mostly through oil drilling...
products.
Most of cargo operations are taking place between a ship and a land-based terminal. Nevertheless it sometime can be useful to transfer cargo from one ship to another in open sea and this is called a ship-to-ship operation. At that moment, one of them will act as the terminal where the other one will moor. The receiving ship is called the mother vessel.
Reasons for
- Lightening a vessel prior harbour entering or for re-floating
- Bunkering operation
- Earning time in a really 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
| 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
This manoeuvre is designed for a vessel with a high manoeuvrability which approaches such a big vessel that it can be considered as a reference on its own. At that moment the mother vessel can maintain her course and slightly decrease her speed to reduce her bow-wave and the small vessel will approaches to finally get on a parallel track.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.
Regulations
These operations are carried out in accordance with guidelines set out by the Oil Companies International Marine ForumOil Companies International Marine Forum
The Oil Companies International Marine Forum is a voluntary association of oil companies having an interest in the shipment and terminalling of crude oil and oil products....
and the International Chamber of Shipping
International Chamber of Shipping
The International Chamber of Shipping is the world's principal shipping organisation, representing around 75% of the world’s merchant tonnage; through membership of national shipowners' associations, concerned with all regulatory, operational and legal issues....
(ICS), with the strictest adherence to safety regulations.
According to International Maritime Organization
International Maritime Organization
The International Maritime Organization , formerly known as the Inter-Governmental Maritime Consultative Organization , was established in Geneva in 1948, and came into force ten years later, meeting for the first time in 1959...
regulations vessels transferring OIL CARGO must have an approved STS operational manual that describes the procedure. 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.