ACCURACY CONSIDERATIONS IN TANK SOUNDINGS AND ORB VOLUME RECORDING

Since there is an, often misconstrued, assumption that ORB measurements are bookkeeping records (as in the dollars have to add up), rather than engineering measurements, very significant disputes can arise when the numbers do not appear to “add up”.

As such, a methodology needs to be established with regard to shipboard tank measurement and recording that passes appropriate and reasonable engineering standards, which then can be applied to ORB volumes.This document establishes such a standard.

Recording conditions truthfully in the ORB can never get anybody in trouble therefore do not interpret and adjust records to make the ORB look “nice”

Basically it says the standard is record to the nearest tenth. So 3.0 + 0.02 = 3.0

The information is +/- 0.4 at best but is recorded to the nearest 0.1 so that results in an inherent inconsistency:

Worst case volume transfer accuracies are expected to be in the range of +/-0.4 cubic meters (+/-0.2 cubic meters level measurement plus +/-0.2 cubic meter conversion accuracy) in optimal conditions (no seaway, etc.). At the same time it is known that measurement accuracies of 0.01 cubic meters are not achievable even on the smallest tanks.

The above indicates that measurement recording to 0.1 cubic meters accuracy is barely achievable, and that on tank volume records, depending on the tank and conditions, the last digit (representing a tenth of a cubic meter, 100 liters) is inherently questionable.

It does seem like it would be helpful to have written guidance aboard that people could follow.