One of the most vital aspects of trading with tanker ships is loading and unloading of the cargo with utmost safety and efficiency, without polluting the marine environment.
Safety of cargo operation implies and includes pre-planning of the cargo before the quantity is nominated and the fixture (Consists of approximate quantity and nomination of cargo, including details of charter parties, load port and disport particulars) is made.
Environment protection is very significant in respect to the large quantities of oil and chemicals, which might get discharged into water as a result of accidental oil spills or human errors.
Sometimes the quantities are large enough to disrupt the entire biological chain of the marine environment in that area and to cause adverse effects of marine pollution.
Cargo Pre-loading Preparation
- Charterers, before fixing a vessel on a particular voyage, generally ask for quantities of cargo the vessel can load. Few relevant points are to be practiced by the shipboard staff involved with the procedures.
- While advising the charterers about the maximum quantity to be loaded, the quantity must be in compliance with company requirements if any.
- The quantity to be loaded must be evaluated against the damage stability conditions of the ship and for compliance with minimum stability requirements for tankers.
- Load line zones throughout the voyage to be checked for maximum loadable quantity. Sometimes vessels load in summer zone and pass through winter zone. Hence considering winter zone transit in mind, quantity of cargo to be loaded must be ascertained.
- The voyage instructions must be checked for full details of nominated cargo including quantity, quality, carriage and discharge. If relevant details are missing, charterers can be asked to provide them.
- The vessel must be able to maintain any segregation requirements for different grades throughout the voyages. This includes vapor segregation too. Instructions for segregation are provided by charterers. E.g. segregation of Naptha and Jet Oil or certain dyed Gas Oils require segregation of vapors as well due to difference in Sulphur Content.
- Suitability of cargo tanks is a major issue with carriage. Certificate of fitness which is issued to tankers that can carry particular types, nature and grades of cargo , determines whether a vessel is fit to load a particular type and category of cargo or not. Tank coating and material plays an important role in determining this. E.g. certain paints used as tank coating react with cargoes and lead to contamination.
- All cargo tanks and lines must be prepared to load suitable cargo. Wash water or remains of previous cargo must be completely removed from tanks and lines. E.g. Some type of cargo like jet fuel can get contaminated by water .Surveyor can reject a vessel for loading if they find any remains of wash water or previous cargoes.
- Some cargo like various grades of crude oils, laguna etc. require heating. The instructions for the same are provided by charterers. Vessel needs to study these instructions carefully to ascertain if the vessel can comply with these instructions for appropriate carriage throughout the voyage and efficient discharge. If any queries, doubts arise same must be notified with the charterers. Eg. Few terminals in UK or US do not accept cargoes if they are found at temperatures above or below that specified in the voyage orders or as per charterer’s instructions.
- During the entire voyage if cargo heating is required during the loaded voyage, the temperature of lower, middle and bottom of the tanks must be recorded along with daily ambient temperatures of air and sea.
- Various crude oils require COW (An abbreviation used for Crude Oil Washing). The cargo must be checked for suitability to COW. Also the requirements of terminal must be noted with regards to COW.
- The density of cargo should be checked carefully and examined for the maximum allowable capacity of tanks. In any case it should not exceed the maximum weight designed for ship’s tanks.
Ullage
The ullages to be loaded should be determined as under:
The maximum quantities to be loaded should also take into consideration air and sea water temperatures, which play an important role in changing the volumes of cargo inside the tanks, especially when tanks are loaded above 95%.
E.g A ship loading in Russia and Unloading in Persian gulf must consider the fact that the range of temperature difference of cargoes at load port and discharge port can get as high as up to 40 – 50 degrees in extreme cases.
Did you subscribe to our daily newsletter?
It’s Free! Click here to Subscribe!
Source: marine insight
