De-ballasting

In both cases these measurements can be varied by ballasting or de-ballasting various tanks, but it must not be overlooked that a dry cargo vessel’s ballast tonnage capacity will almost certainly be far less than her deadweight capacity. Thus, a fully ballasted vessel will be higher out of the water than if she was loaded and where height restrictions are severe, calculations should be carried out on the basis of a vessel being fully ballasted – not loaded. Other important dimensions include: The length and breadth of hatchways and, for general cargo ships both weatherdeck and tweendeck hatchway sizes. It is occasionally the case, usually with bulkcarriers manoeuvering beneath shore cargo handling equipment, that it is necessary to know distances from a ship’s rail to the inside edge of her hatch coamings and to the far side of the hatchway, as well as the length overall from forward of the foremost hatchway to aft of the aftermost hatchway. Tank Tops and Decks:  The square floor area/dimensions of a vessel’s hold bottoms and decks, also the height of holds and tweendecks. Strength in tonnes per square metre must also be known for any part of the ship where cargo will be loaded. Although a few of the larger and older vessels (e.g. ore/oilers) are equipped with steam turbines,the majority of dry cargo vessels are today powered by either slow speed or medium speed diesel engines. Particular attention is paid in modern ships to the fuel preparation equipment, thereby enabling vessels to burn low cost residual Intermediate Fuel Oils (‘IFO’) efficiently and without harm to the engines. Increasingly engine makers are modifying new engines to burn even heavier oils which are cheaper to buy. Although a few very modern types (referred to frequently as ‘eco-types’ – ‘eco’ being short for ‘economical’) use IFO in both their main and auxiliary engines, many vessels consume Marine Diesel Oil for their auxiliary equipment (e.g. generators), and all vessels carry some MDO on board for possible use when a vessel is entering or leaving port and/or whilst navigating in confined waters.