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Despite the best efforts of the crew, there are some occasions when it is not possible to discharge all of the cargo tanks to an empty condition. This may be due to the nature of the cargo, or to a performance defect in the ship's equipment.

5.35.1 ROB cargo

Legend: S - Measured innage at gauge point. A - Total 'A' - adjusted innage at after bulkhead. A1 - Upper portion of 'A', above the bellmouth HT. A2 - Lower portion of 'A', below the bellmouth HT. Method: First calculate wedge volume using total 'A'. Then calculate unpumpable wedge volume using the A2. Subtract unpumpable volume (if any) from total volume. Note: Never use reference tank width for the wing tanks, as it is wrong, because of the bottom curve and structure. Wedge calculation for wing tanks should be made using the calculated width of tank at its bottom - see plan.

Whatever the cause, should the final inspection or gauging certificate, as prepared by the terminal representative or independent inspector, indicate that the ship has 'pumpable' or 'pumpable cargo remaining' quantities on board, then the master should take the following actions:
Refuse to disconnect the cargo hoses.
Refuse to depart from the berth.
Endorse the tank inspection certificate either 'for receipt only' or 'receipt acknowledged without prejudice'.
Invite, in writing, representatives of the concerned parties to attend the vessel and witness a demonstration of the cargo stripping pumps properly lined up to the tank(s) in question. Record the events of the demonstration and the names and affiliations of persons attending. Note the names of any who refuse to attend. This demonstration will be impossible if the ship strips its cargo tanks with eductors. If eductors are used for stripping the chief officer should have all except the final tank inspected before the last tank (containing the last eductor drive fluid), is discharged.
After the demonstration, present a second letter of protest which describes the details of the demonstration and which indicates that the stripping equipment is unable to remove the un-pumpable sediment from the vessel's tank bottoms.
Obtain a certificate indicating the arrival API of the vessel cargo (if viscous cargo), or the RVP if a cargo with high vapour pressure.
Present a protest letter regarding any shore terminal intention to drain or blow the loading arms/hoses into the ship's pipelines or tanks. Indicate that the vessel will not be responsible for any cargo which the shore voluntarily returns to the ship's tanks.
When port safety regulations permit, attempt to recover a clear sample of any cargo remaining on board. Each tank containing ROB should be sampled. Do not consolidate or commingle the samples.
If the ROB is liquid, a correct wedge formula calculation should be used to calculate the amount remaining in the tank, with an appropriate deduction for the amount of liquid which will be below the suction bellmouth (best possible recovery).
Charter party clauses generally stipulate that freight will be deducted if the volume of cargo ROB is pumpable as determined by independent surveyor. Unless otherwise qualified, almost every
surveyor now uses 'liquid' and 'non-liquid' as descriptive terms. The area between these terms is grey, but it has been determined on several occasions that if a letter of protest is not issued by the surveyor or terminal and if samples have not been obtained, then 'pumpability' has not been proven. Although the term is not universally recognised, we cannot ignore the oil residues which fall between liquid and non-liquid. These are frequently called 'ooze' or 'sludge' and have been recognised by well known arbitrators. The description of 'ooze' permits the supposition that non-liquid ROB can be calculated by a wedge formula, provided that many dips are taken to determine the true thickness. Many independent inspectors are not permitted the luxury of making their own classification of ROB due to instructions from their employers.
If the ROB material is semi-solid, take innages in as many areas of the tank as possible, to more accurately determine the quantity of material in the tank.

Any ROB must be identified on the tank inspection certificate as:
'Un-pumpable sludge'.
Cargo 'un-reachable by vessel's means' (draining blocked by sediment, below suctions etc., (see figure 5.35.1), or
'Pumpable cargo' which vessel's pumps are incapable of pumping ashore due to vessel defect or high shore back pressure.

5.35.2 ROB use as fuel
If the ROB is from a cargo of fuel oil, the residual cargo may be collected by bottom flushing the tanks and stripping the tanks to an accumulation tank. This will recover about 90% of the ROB, without forming the emulsions which water washing would produce.
If there is any doubt about the flash point of the recovered cargo, it should be tested before transfer to the fuel tanks. If the flash point is above 60 C, then it may be used as ship's bunkers, provided the remaining specification are within the requirements set by the engine's manufacturer.
Accurate records must be maintained of the transfer of the recovered oil to the fuel tanks. If this is not done, the ship may be subject to later claims for cargo diversion.
Test for sodium and vanadium content in the ROB are desirable when timely results will be available.

5.35.3 Off-test cargo
On some occasions, the master or chief officer will learn before the cargo discharge commences that a portion of the ship's cargo is off-test.
Owners and the local representative of the P&I Club must be notified immediately, indicating all principal details as known or understood at the time. The chief officer should immediately perform the necessary calculations to determine if and how the remainder of the cargo can be discharged safely without exceeding the allowed hull stress factors. If the balance of the cargo cannot be safely discharged, then the vessel may be required to vacate the berth and await orders from the owners or charterers.
Owner's and the P&I Club may wish to engage an alternative, independent petroleum inspection service to sample the allegedly off-test tanks and to perform the necessary tests to confirm the condition of the cargo. The chief officer should in any event, sample the suspect tanks and retain the samples for later evaluation.
The cargo may have been determined to be 'off-test' based on the anticipated additional quality degradation incurred with routine cargo discharge. If that is the case, the potential for special ship and shore line preparation (draining and flushing), to eliminate further handling degradation should be evaluated.
If the discharge stress analysis determines that the balance of the cargo can be safely discharged, then the ship should proceed to do so, reserving the allegedly off-test tanks. Tank suction valves on the off-test tanks should be sealed to prevent accidental discharge. The owners must be kept closely advised of the progress of the discharge with an indication of the expected completion time. If the disposition of the off-test cargo is not decided when the balance of cargo is finished, then the vessel may be required to vacate the berth and await orders.

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