In various tanker trades, both dirty and clean, it is commonplace for vessels to load and discharge cargo via Ship-to-Ship (STS) transfer. However, there is one aspect of STS cargo transfers is not so clear-cut; should either or both vessels apply their respective Vessel Experience Factor (VEF) when assessing how much cargo has been transferred and received between the two?
UK P&I Club’s Senior Claims Executives Christos Aporellis and Alec Kyrle-Pope examine whether vessels should apply their respective Vessel Experience Factor when assessing how much cargo has been transferred & received in ship to ship transfer to avoid cargo claims.
Quantity & Condition
Just as with many other segments of the shipping industry, in the oil trade, cargo claims can often be divided into two broad categories; those relating to quantity of cargo as delivered and those concerned with the condition of the cargo as received.
In the main, cargo shortage claims on outturn tend to be the greatest source of issue but many of these, if not the vast majority, can frequently be explained because of a “paper” loss rather than an actual physical disappearance of product. This is not to say that oil cargoes, particularly unrefined crude, do not change volume (due to temperature) or emit gases on route nor are they any less susceptible to factors such as “clingage” or unpumpable Remain On Board (ROB), but the point remains that most major inconsistencies arise due to errors in cargo accounting. Whilst the carrier may be exposed to the risk of cargo loss during loading, transit, (discharge, and (subsequently (OBQ/ROB losses) it would seem self-evident it is at loading and when the vessel receives her intended cargo that any margin for error remains within the carrier’s control. This is where careful measurement becomes key.
Pump up the volume
The movement of oil and its products is best understood and measured in terms of standard volume rather than weight. Assuming there is no impediment to the assessment of a standard volume (with reference to a prescribed temperature), one then has to ascertain the cargo’s actual volume, as transferred, by reference to the volume of the spaces it has been moved to and from.
Typically, this is done by ullaging the headspace in the tanks and consulting the relevant calibration tables to determine the actual volume of those tanks the cargo now occupies, commonly referred to as the Total Observed Volume (TOV). Assuming this process is performed accurately (e.g. consistent datum points, allowances for vessel’s list and trim, repeat measurements in poor sea conditions) and once a standard volume metric has been applied , then it should become apparent how much cargo resides in the cargo spaces in question.
This is where a Vessel Experience Factor comes into play. For any given vessel a ratio can be established between the quantity of liquid bulk cargo measured onboard the vessel and the corresponding measurement reported ashore, typically, by a loading facility or terminal. This ratio, called a Vessel Experience Factor (VEF), is an empirical data stream of shore-to-ship cargo quantity differences collated from previous voyages, and is used as a loss control tool to assess the validity of quantities derived from external sources. It is as such both a means by which to correct any calibration error and a method to verify cargo quantities established onboard the vessel compared to what has been declared ashore.
Generaly, the definition of a qualifying voyage is one that meets the following criteria:
- Includes any voyage that is within a margin of +/- 0.0030 of the average ratio of all voyages listed.
- Excludes any voyages where calculated ratio suggests significant error.
- Excludes the maiden voyage, and any voyages prior to any structural modifications affecting vessel’s cargo tank capacities.
- Excludes any load or discharge data where shore measurements are unavailable.
- Excludes the first voyage after a dry docking. (N.B. not necessarily applicable in clean products trade.)
- Excludes any voyages after the carriage of non-liquid cargoes.
Further details about the STS Cargo Transfers & VEF may be found by reading related article at latest publication of the UK P&I Club ”Hellas Hilights” – December 2015 Issue 33
Source: The UK P&I Club
