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This article focuses on the importance of knowing industry standards for assessment of crude oil cargo remaining on board (ROB), when measuring ROB quantity upon completion of discharge. Improper procedures for measuring ROB quantities may lead to excessive ROB assessments and consequential claims for shortage and/or deductions from freight under the so-called cargo retention clauses.

An article about ROB claims and assessment procedures appeared in Gard News issue No. 118. However, the number and value of ROB claims seem to be on the rise, probably due to the increase in crude oil prices. Therefore, a reminder is appropriate.

What is ROB?
One industry standard1 defines ROB as "the sum of liquid volume and non-liquid volume in cargo tanks just after completion of discharge, excluding clingage, hydrocarbon vapours and the contents of associated pipelines and pumps". However, not all ROB cargo will give rise to claims. Cargo receivers and/or charterers may concede that some crude oil becomes non-liquid in the course of the voyage and hence can not be pumped. Moreover, it is normally accepted that some liquid cargo may remain on board because it is beyond the reach of the vessel's pumps.

What is frequently in dispute is:
(1) the total quantity of cargo (i.e., liquid and non-liquid) remaining on board;
(2) the quantity of liquid cargo remaining on board in comparison with non-liquid cargo;
(3) whether or not the liquid cargo is pumpable and in fact can be reached by the vessel's pumps; and
(4) if the liquid cargo can not be reached, whether or not this is due to any fault, neglect or technical condition for which the carrier is liable.

Industry requirements for ROB surveys
Upon the completion of discharge of a crude oil tanker, an independent surveyor performs an ROB survey and subsequently issues an ROB certificate, which becomes the core piece of evidence concerning the quantity of cargo remaining on board. It is a difficult task to determine the ROB quantity on board a crude oil tanker correctly. The tanks are usually very large and one dip only measures the quantity located exactly under the dipping point, which again is only representative of a very limited part of the tank bottom. Furthermore, the tank bottom normally contains structures such as frames and transverse webs, which obstruct free flow of oil to the suction points.

In order to properly measure the ROB, industry standards2 require that the ROB quantity in each tank be measured from at least four positions, that is, at least four dips in each tank. One of these positions must be the reference gauging position as defined in the vessel's tank capacity table. In addition, MARPOL Annex I, Regulation 13 (b) (2) requires vessels to have suitable arrangements for hand-dipping at the aftermost portion of a cargo tank and in three other suitable locations. This means that if four positions are not available for dipping, the vessel does not comply with the MARPOL regulations.

As a minimum requirement the survey should be performed in accordance with the Manual of Petroleum Measurement Standards, Chapter 17 - Marine Measurements, published on behalf of the American Petroleum Institute, or similar guidelines.

Be alert when the ROB quantity is being assessed!
Unfortunately, in contradiction with industry standards, surveyors frequently dip tanks only in one place. Obviously, this may lead to inaccurate assessments of the ROB quantity. To protect the owner's interests, the Master should insist on the surveyor taking four dips in each tank. If the surveyor refuses to comply with the Master's request, a letter of protest should be issued.

Some ports do not permit vessels to open tank hatches or other accesses which allow inert gas to escape. This may prevent proper application of assessment methods as set by industry standards. In such circumstances, a letter of protest should be issued to highlight this restriction and the potential consequences, i.e., potentially inaccurate ROB readings.

The vessel's crew should closely monitor how the ROB survey is conducted. If liquid hydrocarbons are found, proper investigation should be carried out without delay in order to determine whether the liquid is pumpable and reachable by the vessel's equipment. Some surveyors refuse to formulate any opinion in this regard. If this happens and/or if there is disagreement between the Master and the surveyor on this point, the Master should make an appropriate comment on the ROB certificate and preferably also issue a separate letter of protest.

To support the fact that the liquid ROB is not reachable by the vessel's pumps, an accurate log should be kept during stripping operations. This log should contain a record of the procedures followed and all times when loss of suction have occurred in each tank. It should also contain comments regarding how the loss of suction was detected. For example, a "zero" reading on the pump discharge pressure gauge, racing of the pump and an increase in the temperature of the pump casing may all be indicative of loss of pump suction. All of these readings can be used to underscore the fact that the ship has done everything possible to remove the cargo and that whatever liquid is remaining on board is not reachable by the vessel's equipment.

Final comments
Although some crude oil carrier operators are facing bonanza market conditions, close attention should be paid to the tendency that charterers, cargo shippers and receivers have to claim in respect of cargo remaining on board under such conditions. To defend claims on the basis of inaccurate ROB certificates may be an uphill struggle, unless the Master has made express reservations at the relevant time. A high degree of awareness is therefore warranted both on part of the Master and the owner.

Gard Services or its local correspondents should be contacted for assistance in case problems involving ROB cargoes arise.


1 ISO 8697:1999(E) (Crude petroleum and petroleum products -Transfer accountability - Assessment of on board quantity (OBQ) and quantity remaining on board (ROB)), issued by The International Organization for Standardization (ISO).
2 ISO 8697:1999(E).


Gard News is published quarterly by Gard Services AS, Arendal, Norway.