cargoes to be loaded in more than one port and for several discharge ports to be involved. In some cases, additional cargo may be loaded during the voyage after the discharge of other products. Careful planning is advisable taking into consideration the quantity of cargo to be loaded and discharged, draft, trim and stress considerations as well as the consumption of water and fuel.
Before loading, all those concerned should have a clear knowledge of the intended loading plan and the pipelines and valves must all be carefully set and double-checked. Because product cargoes generally have a low specific gravity, it is likely that the ship may not be loaded down to her marks even with all cargo tanks filled to the maximum permissible. When loading for a voyage which entails passing through areas where higher sea temperatures are expected to be encountered, it is advisable to take into account the expansion of the cargo which will occur as a result of those higher temperatures.
During the loading of sensitive products it is common for ‘foot samples’ to be loaded and for samples to be taken and analysed before the rest of the product is taken onboard. When carrying multigrades it is an excellent practice to have as many samples of the cargo as possible taken at various stages of the loading and discharge, including samples taken from the shorelines. If claims for contamination arise, the analysis of such samples will often identify the source of the problem and may assist the shipowner in rejecting liability.
A more detailed article on the sampling of liquid cargoes is included later in this section, and a careful study of that article is recommended.
Conclusion
If the following points are borne in mind by owners and masters there will be a much greater chance of success when defending oil cargo claims.
● Careful attention should be paid to all onboard surveys when loading and discharging with a view to avoiding ‘paper losses’
● After discharge try to ensure that a dry tank certificate is issued showing all cargo remaining onboard to be unpumpable and endorsed to confirm that the ships equipment was working correctly
● Employ properly qualified surveyors and protest if it can be demonstrated that a surveyor employed by cargo interest is not qualified or lacks experience.
Appendix:
definitions of terms used API = API GRAVITY
Petroleum industry expression for density of petroleum liquid expressed in API units. API gravity is obtained by means of simultaneous hydrometer/temperature readings, equated to, and generally expressed at 60°F. The relative density to API gravity relation is:
141.5 Relative density 60°F AUTOMATIC SAMPLER
A device installed for indicating the level of product from a location remote to the manual gauge site.
BARREL
Petroleum industry measurement unit equal to 42 US gallons.
CLINGAGE
That oil remaining adhered to the inner surface and structure of a tank after having been emptied.
CRUDE OIL WASHING (COW) The technique of washing cargo tanks of oil tankers during the discharge of crude oil cargoes.
DENSITY
The density is the mass per unit volume at a specified temperature used to determine weight for a volume at a standard temperature.
DIP
Is depth of liquid = to American expression: gauge.
FREE WATER
The quantity of water resulting from measurements with paste or interface detector, i.e. not entrained water present in oil.
GAUGE REFERENCE HEIGHT The distance from the tank’s strike point to the bench mark or reference point.
GROSS OBSERVED VOLUME (GOV) The total volume of all petroleum liquids, excluding S&W, excluding free water, at observed temperature and pressure.
– 131.5
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