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Ship-to-Ship Transfer of Hydrocarbon Products
Capt. D. N. Banerjee, Lighterage Master, SCI Lighterage Cell A huge quantum of crude oil in the country is derived from foreign lands and are imported in Very Large Crude Carriers (VLCCs). These VLCCs require deep drafted ports. Lightering becomes imperative as the operation reduces a vessel’s draft for it to be able to enter port facilities, which cannot accept very large ocean-going vessels. The article details this, and more of interesting facts about lightering.

The history of the oil tanker is a part of the evolution of the technology of oil transportation alongside the oil industry. Although man’s use of oil goes back to the prehistoric period, the first modern commercial exploitation dates back to James Young’s manufacture of ‘Paraffin’ in 1850.

In the earlier days, oil from Upper Burma was moved in earthenware vessels to the river bank where it was then poured into boat holds. We have come a long way in terms of transportation of oil. Today’s modern Ultra Large Crude Carrier (ULCC) can be as long as 1,300 feet (400 m) long and have a capacity of about 500,000 DWT. With the exception of the pipeline, the most cost-effective way of transportation of oil is by shipping (tankers). Larger the oil tanker, cheaper it is to move oil. Larger tankers have contributed significantly to the growing demands for oil.

Lighterage activity was born as an integral part in movement of crude oil to its ultimate destination; the Refineries. In the Indian subcontinent, at least 80% of the domestic requirement of fossil fuel comes from other oil producing nations and it makes economic sense to import crude oil in larger ships such as VLCCs with capacities ranging from 200,000 to 300,000 Metric Tonnes. However these ships are too large and require deep drafted ports.

Lighterage or Lightering is the process of transferring cargo between vessels of different sizes. Lightering is undertaken to reduce a vessel's draft in order to enter port facilities which cannot accept very large ocean-going vessels.

Effective manoeuvring controls are required on board both the vessel to be lightered and the lightering vessel. A few service vessels are equipped with bow thrusters, controllable pitch propellers, twin screws, and special rudders to aid in manoeuvring. Most also have engine controls on the Bridge and sometimes at other locations. Good systems for communications between key locations onboard each vessel and between vessels are critical.

Lightering vessels may be engaged by a variety of operators and shipping companies. These vessels have a range of design features that make them more or less suitable for lightering activities. Vessels that have been built or converted for lightering, usually service vessels that are dedicated solely to lightering, have standard mooring, fendering, and hose transfer systems built in, and they engage in lightering on a regular basis.

On non-dedicated lightering vessels the mooring lines, fenders, and hoses are usually delivered to these vessels just before a lightering operation, used during the offloading of one Still to be lightered (STBL), and then removed by the service company that was engaged to provide this equipment, expertise, and personnel for the lightering operation. These non-dedicated vessels are of varying designs, so the special equipment must be able to accommodate a variety of on-board arrangements.

STBLs exhibit an even greater variety of designs and arrangements of equipment. An STBL can be any vessel from the world tanker fleet with several possible places of construction, any age, any flag of registration, and crew nationality, and so forth. Other than expertise, three categories of special equipment necessary for the safe transfer of oil cargo between two vessels on the open ocean, the same are listed below:

• a method of keeping the vessels together (i.e., a strong, well designed mooring system)
• a method of keeping the vessels apart and protecting them from each other (i.e., a fender system suitable for the individual operation)
• a reliable transfer system for moving the oil from one vessel to the other (i.e., hoses, connections, and equipment for connecting and disconnecting them)

The side-by-side mooring arrangement used in a typical lightering operation is only practical in low-to-moderate seas under reasonably good weather conditions. If the weather turns severe and waves reach a certain height, the operations must be suspended and the vessels separated. Vigilance and good judgment on the part of all mariners are essential to avoid damaging either vessel.

The OCIMF (ICS and OCIMF, 1997) and individual company standards specify the types and testing of fenders. Before a lightering operation begins, the mooring master or lightering service company representative tests the pressure of pneumatic fenders, which must be inflated according to the manufacturer’s instructions (foamfilled fenders are sometimes used instead). Pneumatic fenders are most reliable when they are fitted with safety release valves to prevent them from bursting when compressed. Primary fenders, which absorb the impact from the connection of the two vessels, must have the proper diameter in relation to the vessel’s freeboard to prevent the fenders from riding up the sides of the vessel and rolling onto the deck.

The OCIMF recommends that fender diameter not exceed half the freeboard at any time. The fenders should also provide maximum protection along the hull, allowing for both approach and departure angles. Experience and skill are required to place fenders properly because vessels meet at different angles. The speed of approach significantly affects fender requirements, and it is prudent not to overestimate the approach speed when selecting fender size. The fender rigging system is also critical.

Secondary (or “baby”) fenders provide additional protection in case the angle between the vessels exceeds the protective capability of the primary fenders. Secondary fenders are placed fore and aft of the primary fenders to prevent steel-to-steel contact. The flare and counter of the two vessels aggravated by motion, results in an almost infinite number of possible contact points. Tankers have extensive parallel mid-bodies, where fenders work best. However, some modern vessels have short parallel mid-bodies, so secondary fenders must be available in appropriate locations. Fenders may have to be moved or adjusted to suit the situation. Some vessels that are routinely engaged in lightering are fitted with permanent mounting points to facilitate the handling of secondary fenders. Some operators of dedicated lightering barges have placed permanent moulded-rubber fenders on the sides at these contact points, which eliminates the need to deploy fenders for each lightering operation.

Many types of hoses are used in lightering. All of them must be approved by the administration for this service. The transfer hoses have a thick outer rubber jacket with an inner liner for reinforcement. Hoses are generally connected to the manifold by means of a fully bolted flange, which provides a strong and reliable connection. Hoses should be inspected regularly because they are exposed to more wear during lightering operations than when they are used at a terminal.

Weather is a major risk factor in lightering. Weather is both a safety factor, and a legal factor, because winds and sea state can affect vessel interactions, OCIMF guidelines specify the weather conditions under which lightering may take place in the designated lightering zones. Thus real-time information about the weather on the scene of the lightering operation, at locations six to eight hours away, and as much as 24 hours in the future should be available. As the two vessels come together, vessel operators use information about winds, currents, and sea state to the best advantage. This information also ensures that the vessels will not be "peeled apart" during the approach. Once the vessels are safely moored together, the weather is continuously monitored to ensure that conditions do not deteriorate to the point where safety is compromised. Sea state, winds, and currents also affect the unmooring of the two vessels.

If it appears that weather may become marginal, then the operators have several options. They may terminate cargo operations, drain the hoses, and keep the vessels together until the bad weather passes; terminate cargo operations, drain the hoses, and separate the vessels with the intention of coming back together later to finish transferring the cargo; or continue operations. Interrupting an operation and dismantling connections takes time, so the longer the lead time the lower the risk associated with unmooring. When the weather is deteriorating, it is important to have accurate forecasts that give operators sufficient time to unmoor and move the vessels apart before the weather becomes too severe to accomplish this safely. Lightering is done most efficiently and safely while the STBL is at anchor.