The Vessel Experience Factor (VEF) plays a crucial role in shipping operations, particularly in the oil and gas industry. This factor helps determine the accuracy of a ship’s cargo measurements, offering valuable insight into the discrepancies between ship and shore figures during loading and discharge operations. In this article, we’ll explore the significance of VEF, how it's calculated, and its practical implications on shipping operations.
The Vessel Experience Factor is essentially a calibration metric that reflects the historical difference between the cargo measurements taken on the ship and those taken on shore. These differences are typically based on the last 10 loadings a vessel has completed. The VEF provides a way to evaluate whether the ship’s onboard measurement systems are calibrated accurately over time.
VEF is often used by the Chief Officer to assess whether the bill of lading (B/L) quantity is reliable. By comparing the ship's figures with the shore's, potential shortages or excesses in the cargo can be identified before departure.
The accuracy of the VEF is essential for the following reasons:
It ensures the ship's loaded quantity is precisely determined based on consistent calculation procedures.
It provides a safeguard against inaccuracies in the bill of lading, preventing misreported quantities that could lead to financial and legal complications.
VEF offers early warning signs if there's a mismatch between ship and shore figures, allowing timely action before the ship sets sail.
In cases where the ship is not properly calibrated, significant discrepancies between the actual quantity and the bill of lading might go unnoticed, leading to unreported short-loadings or incorrect cargo deliveries.
VEF is generally only applicable to a fully laden ship, meaning it's not always relevant in cases of part loadings or individual tank measurements. While some ships maintain a tank-by-tank experience factor, this is typically for vessels engaged in parcel trades where each tank represents a separate consignment.
When more than one grade of cargo is loaded, VEF can only help assess the total bill of lading quantity. This means that while it can verify the overall reliability of the loaded cargo, it may not be effective in evaluating individual bills of lading for each grade.
Accurate determination of VEF is crucial for smooth shipping operations. VEF cannot be approximated, as stating the ship's figures are "higher by about 200 tonnes" is not precise enough. There are at least three approved methods for determining VEF, as published by API and IP (Institute of Petroleum).
One of the most reliable methods is the statistically rigorous IP Method 2, which can be used by ship officers in place of the simpler field method. Ships equipped with personal computers can easily perform the necessary calculations and maintain up-to-date VEF records.
The VEF of a vessel is not static and can fluctuate due to a variety of factors:
Changes in trade (such as different cargo types and loading ports).
Accumulation of sediment and scale inside the ship's tanks.
Dry-docking operations where the ship undergoes maintenance, including de-scaling or structural modifications.
After any structural modifications to the cargo spaces, previous VEF calculations become obsolete, and all prior voyages should be disregarded in future VEF assessments.
The main purpose of VEF is to provide insight into discrepancies between the ship’s onboard cargo measurements and those taken at shore. On average, VEF values for tankers fall between –1% to +1%, with a global average of –0.2% to +0.2%.
Being aware of VEF helps the ship's officers detect when the bill of lading quantity overstates or understates the true quantity. For instance, if the ship’s calibration indicates a potential overstatement of 0.8% in the bill of lading, a recalculation might lead to a formal protest if necessary. However, an uncalibrated ship could let such short-loadings go unnoticed.
Industry guidelines dictate that each loading or discharge operation should adhere to a VEF-based tolerance of 0.3% or two standard deviations of the ship’s calculated VEF. When ship-to-shore discrepancies exceed this threshold, it signals the need for rechecks of all cargo measurements.
When a ship is loading cargo from another vessel (known as a mother tanker), the experience factors of both vessels need to be considered. This is a challenging process as the difference in figures could be influenced by several factors such as:
The number of tanks discharged from the mother tanker.
Whether the mother tanker performed Crude Oil Washing (COW).
The nature and type of the cargo being transferred.
Given these complexities, it’s essential to obtain as much information as possible from the mother vessel to ensure both quantity and quality of the loaded cargo are consistent.
The VEF also serves as a measure of the calibration error within a ship's cargo tanks. This error often stems from poor calibration of the tank’s bottom-most parts, which can be affected by the tank's structural elements or hull curvature. These errors could impact the accuracy of the on-board quantities (OBQ and ROB) recorded, leading to misreported loaded or discharged quantities.
With the introduction of electronic gauging systems, adjustments are often required to the reference height of each tank. These adjustments, made retroactively, could alter the observed ullage and impact the final volume measurements. Any change in ullage position directly affects corrections applied for changes in the ship’s trim and list, making it vital that calibration tables are kept up-to-date and clearly indicate where ullage should be taken from.
In conclusion, the Vessel Experience Factor (VEF) is an indispensable tool for ship officers in ensuring the accuracy and reliability of cargo measurements. Regularly updating and accurately calculating the VEF allows for effective management of potential discrepancies between ship and shore measurements. It plays a significant role in avoiding financial and operational discrepancies in shipping, thereby safeguarding the vessel’s cargo operations.
