Cargo Quantity

On the assumption that there are no draft limitations anywhere on a voyage, it may be sufficient just to know a vessel’s available deadweight in order to assess cargo capacity, otherwise adjustments must be made in accordance with available draft. From the eventual available tonnage must be deducted the vessel’s constant weights (consisting of stores, fresh water, lubricants, spares – even the weight of the crew). A vessel’s constant weight is rarely critical but must be accounted for. (For vessel of around 15/25,000 tonnes sdwt it will be about 250/350 tonnes and, for vessels in excess of, say 35000 tonnes, some 4/500 tonnes). The other important deduction is that of bunkers remaining on board a vessel, and here it may be necessary to obtain appropriate data from the vessel’s managers or from her Master. Suffice at this stage of the Lesson to be aware of bunkers constituting a major consideration. In the meantime, let us assume we have reached a suitable figure for deadweight cargo capacity. Regrettably this is not the end of the problem. In theory, by dividing a vessel’s grain or her bale capacity by the stowage factor of the cargo to be loaded, we reach volume capacity. This maximum amount of cargo that can be carried within available cargo compartment space must then be compared with the available cargo weight. The smaller quantity is the restriction with which the vessel’s operators must comply. It is normally the available deadweight which proves to be the limiting factor but, occasionally, a high stowing cargo such as coke or certain agricultural products will restrict tonnage intake. Also it may be necessary to load several grades or types of cargoes, each requiring a separate cargo compartment and possibly causing, therefore, an inability to use all a ship’s cargo space. The voyage estimate form provides space for draft, deadweight and cubic capacity calculations under the appropriate heading.