Loading Aspects, Trim and Ballasting Overview
Container ships and general cargo ships will generally have a good deal of scope for improving stability and changing trim using ballast tanks as they normally have more smaller tanks rather than fewer large ones as in ships that carry bulk cargo. Ships on liner runs with several ports where they may load or discharge cargo or do both in the same port will need to carefully consider the best way to maintain stability and trim as well as maintain a high load factor as their draft may change several times in a voyage. It is also very important to make sure that the propeller and rudder are adequately submerged during the voyage for ship steering and safety purposes, particularly on ballast voyages as well as reducing fuel costs and GHG emissions. In addition to wasting fuel as the propeller may be out of the out of the water, if the wind force increases, the ship can start to roll violently putting the safety of the crew at risk and make it extremely difficult to berth unless tugs are available; thus delaying the vessel and also wasting fuel and increasing GHG. It should also be taken into account that over the life of a ship, the light ship displacement will increase due to a build-up of paint and bio growth on the hull and mud in the ballast tanks, thus leading to a reduced the cargo load capacity (MariEMS 2017).