The Ultimate Guide to Cargo Operations for Tankers

Cargo Operation

CHAPTER 2


Cargo Loading

Cargo Unloading

Stripping

Loading of cargo from shore can be carried out indifferent ways such as
• By gravity
• By shore pump
• Through ship to ship transfer Oil tankers, nowadays, also load directly from the oilfield located at sea. To perform the loading operation, the tanker is moored up to a floating buoy or turret, or to a gantry. Many tankers perform cargo operation using an advance loading system, combining a Bow Loading (BL) system and a Submerged Turret Loading (STL) system (connected to the bottom of the ship via mating cone. The Floating turret system also enables the vessel for mooring as well as for transfer of the oil from bow to the midship manifold. When ships are moored in a port or jetty, the oil cargo is usually transferred using an articulated arm
33. l Marine Insight
Cargo Loading
Cargo Operations for Tanker I 34. Floating Turret

Loading oil cargo in a tanker ship is a critical operation as there are associated dangers (oil pollution, fire, explosion etc, whose prevention require utmost diligence in planning and a full attention from the ship's staff at all stages of the operation. Let us assume that a tanker vessel A has a capacity of
50,000 MT of cargo to be loaded through closed loop system. It has 3 mainlines leading from manifold to deck and
6 set of cargo tanks and 2 slop tanks namely 1W‟s,
2W‟s, 3W‟s, 4W‟s, 5W‟s, 6W‟s, Slop W‟s. The cargo tanks are grouped by three color-coded lines on deck namely Red (1W‟s, 4W‟s), Blue loading/discharge system. A terminal may have 2 -5 arms which are used for different purposes usually two arms for loading and one for vapour return. These are directly connected to the tankers manifold located near the center of the ship.
35. l Marine Insight Before starting the loading operation, it is extremely important to lineup the cargo tanks nominated for loading Cargo Operations for Tanker I 36. Articulated Loading Arm in Port

(2W‟s, 5W‟s), and Yellow (3W‟s, 6W‟s and Slop
W‟s). The process of loading is as follows First Foot Loading This stage involves loading up to afoot or more in one of the tanks or all tanks. Samples are then taken for analysis to find out whether the tanks are free of residues from the previous cargo and are cleaned. If it is decided to load the red group first using the red line, the lineup procedure would require all the manifold valves on the deck and other cargo valves of the system to be closed
• Inert gas deck main isolation valve to be closed
• The manifold watch person must physically confirm the cargo passing through the red line only
• In cargo control room, the ullage display for 4W‟s tanks will show change upon receiving. However, this should be manually confirmed with the help of an ullage interface detector tape
• Once it is established that the cargo is flowing into the tanks, other manifold crossovers can be opened so that cargo can enter remaining lines, i.e. blue and yellow, to join their respective group of tanks
37. l Marine Insight Cargo Operations for Tanker I 38. Red, Blue & Yellow Cargo Lines

• The initial rate which was 500 m3/hr can be increased to the maximum permissible rate as decided
• The flowing of cargo into other lines and the filling of the remaining tanks must be confirmed using
UTI. The deck, manifold areas, pump room should be checked for leakages
• As the loading is in progress, the de-ballasting operation should run simultaneously to comply with the loading plan, which describes various stages with cargo and ballast quantities, along with shearing forces, bending moment, drafts, trim and GM
• While de-ballasting, two ballast pumps can be used to keep the vessel upright
39. l Marine Insight The maximum loadable rate of a cargo line is decided by the venting arrangement provided with that particular group. E.g. If PV valves of 4Ws can vent together vapors at 2700m3/hr then the maximum loadable rate for 4W‟s or red line can be up to 2600m3/Hr. Always refer to the Volatile Organic Compound (VOC) manual of the vessel to ascertain the maximum loading rate of a vessel Cargo Operations for Tanker I 40. Checking Stability in Loadicator

Finally, as the tanks come to topping up levels, the ullage should be manually confirmed after every 5 or
10 cm for last 50 cms; and every 1 or 2 cm for last 20 cms. Once 2 groups are finished, and only 4 tanks of a group remain, the rate can be reduced to 500 m3/hr. When all the cargo has been loaded and all the ballast has been discharged, the cargo left in top lines can be drained via bottom crossovers into tanks. The cargo quantities are then ascertained by the mate and the cargo surveyor. The cargo hoses are then disconnected.
• During loading, as far as practicable, the list and trim must be adjusted with the help of the cargo
• Adjusting the vessel with ballast will lead nowhere as ultimately ship has to sail out without any ballast
• All tanks should be loaded evenly. It is preferable to load cargo tanks consistently as per the topping- up sequence
• The final group is decided by choosing the manifold line in which the loading arm is connected
41. l Marine Insight As the tanks reach the level of around 5 meters, the ullages should be reconfirmed with the CCR display using the UTIs. Therefrom, the tanks should be loaded in such a sequence that two groups are properly topped up before the final group fills up for topping up Cargo Operations for Tanker I 42. Good combination for loading can be topping up W s, 6 W‟s and Slop W s, followed by 3W‟s, 4
W‟s and lastly 2W‟s and 5W‟s. Keep 2 and 5 wing tanks in the end as loading these 4 tanks will require one line only and also there wont be any drastic changes in list and trim, to keep the vessel upright

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