Ship To Ship (STS) Transfer: A Comprehensive Guide
What Does Ship To Ship Mean?
Ship to Ship (STS) transfer – also known as lightering – is when two storage tankers moor side-by-side to transfer cargo between them.
These transfer operations usually happen in open sea or at the outer port limit off the coastline.
A STS operation can happen while both vessels are static or underway; which means to travel at low speeds.
Cargoes typically transferred during STS operations include bulk cargo of crude oil and liquefied gas.
Reasons for STS operations will be detailed in a later section.
What Happens In A STS Operation?
In order to carry out a STS transfer safely, specific procedures must be carefully followed. Here is an outline of the basic procedures carried out during STS transfer operations:
Fenders Are Lowered
One vessel lowers its fenders – large inflatable buffers – onto the water. These are to absorb the force of the arriving vessel berthing against it.
They also ensure that no part of the two vessels collides due to the swell at sea.
Ships Approach
The second ship slows as it approaches the first, ensuring that it is correctly positioned to gently berth with the first ship.
Ships Berth
The ships berth, with the two vessels running parallel to each other. Preparations for cargo transfer can now commence.
Hoses Are Connected
Large marine hoses from the daughter vessel are raised to the deck of the mother vessel by crane. Next, these hoses are attached to the cargo transfer outlet on board the mother vessel by its crew members.
Cargo Transfer Commences
Once the hoses are attached to the outlet, cargo transfer can commence. The pumping system on board the mother vessel transfers its cargo to the daughter vessel via the hose system.
Operation Complete
Once the desired quantity of cargo has been transferred, the operation is complete. Next, the hoses are detached and returned to their vessel, one ship separates from the other and the fenders are raised.
Now, the two ships head on to their next destinations.
Additional Procedures
In addition to the main procedures required to carry out STS operations, there are also some administrative procedures that are important to note.
Overall, these are in place to mitigate risks during STS transfer operations.
Regulatory Guidelines
International bodies such as the International Maritime Organization (IMO) provide comprehensive guidelines and regulations for ensuring safety during STS operations.
All crew are required to work in accordance with the prescribed guidelines to promote safety during bulk STS transfers of petroleum products, liquefied gases and chemicals.
Updating Records
The International Convention for the Prevention of Pollution from Ships (MARPOL) lays out specific guidelines for oil cargo transfers.
All transfers between oil tankers must be recorded in the ship’s oil record book to comply with these guidelines. This is so that in the case of a polluting oil spill, MARPOL could ensure accountability.
STS Operation Plan
It is crucial that all vessels which carry out cargo transfer operations have a ship to ship transfer guide and strategy on board, known as the STS Operation Plan.
This should be written in the working language of the vessel and is meant to ensure that STS cargo operations operate smoothly.
It is imperative to regularly review vessels’ equipment and practices to ensure they meet the operational requirements set out by the operations plan.
Operation Coordinator
Between the two ships there must be one person in overall advisory control (POAC) as laid out in the operation plan. This individual is primarily responsible for the safety and success of the operation.
This could be one of the ships’ masters (captains) or a designated ship to ship Superintendent (STSSI).
Why Do STS Operations Happen?
STS operations can occur for a number of reasons, however some are more common than others.
- Vessel is too large: It is common for a port to have what are known as draught restrictions. These refer to the maximum draught of a vessel berthing at port. As a result, the ship may need to transfer some of its cargo to another vessel to reduce its draught. Following this STS operation, the ship may now berth at port.
- Save time and money: Berthing very large gas and oil tankers at port can be time-consuming and incur costly berthing charges. STS operations are often carried out in open sea to avoid these factors, opting to berth smaller vessels at port instead.
- Bunkering: Refuelling ships open happens at sea during a STS transfer. Fuel, or ‘bunker’ is transferred to a vessel by a bunker barge or ship to ensure they have enough supply to continue their voyage. Bunkering at sea is especially common due to the time-consuming nature of berthing a ship at port for bunkering.
- Purge a compromised vessel: In the case that a cargo-carrying vessel is compromised at sea, stranded or leaking, a STS operation takes place. This would avoid the need to wait for repairs to the ship before its cargo is transported. In the case of a leaking ship, a STS operation could avoid spillage, preventing pollution and loss of profits.
Why Safe Ship To Ship Transfer Is Important
The risks and challenges associated with a STS operation are many. Out in the open sea, crews face the possibility of equipment malfunctions, adverse weather conditions and oil and gas spills; each of which could threaten their safety or the safety of their cargoes.
Here are some of the risks associated with STS operations:
- Vessels Collide: The two vessels could collide causing damage to equipment and danger to crew.
- Equipment Malfunction: Malfunction of equipment could occur due to miscommunication or lack of protocol, leading to other hazards.
- Cargo Spill: Crude oil, liquefied gas or chemicals could spill during the operation, posing a hazard to crew and causing potential pollution of the marine environment.
Conclusion
STS operations are a requirement for bulk cargo transfer of oil, gas and chemicals in the offshore industries. Without them the transfer of cargo would be far more costly and time-consuming. However, it is imperative that each STS operation is carried out safely, led by an experienced professional. To learn more about the offshore industries visit our website.
STS Terminology
The delivering vessel is known as the mother vessel and the receiving vessel is known as the daughter vessel.
Another phrase used to describe a ship to ship transfer operation.
Berthing is the process of mooring a ship at port. This has to occur in order to transfer cargo to shore.
Large inflatable devices lowered from the deck of a ship to act as a buffer during STS operations.
A ship’s draught is the difference between it’s keel – the part of the ship which is deepest in the water – and the water line.
