The construction and design of a purpose built inland barge, in most cases, differs from that of an ocean-going barge. This is due to inland barges being built to sail in benign or sheltered waters whereas seagoing barges are designed and strengthened to withstand the stresses associated with sea conditions and heavy weather.
Recently the Club has experienced a number of incidents concerning structural failures to inland barges, leading to sinking during loading and discharging procedures. It has been reported that the causes of these incidents can be mainly attributed to a combination of the construction of the barge concerned and the incorrect loading or discharging procedures. This has resulted in an unacceptable level of stress on the barge structure.
Therefore, when loading cargoes in bulk, it is important that the loading sequence is planned, taking into account the stability criteria of the barge at every stage of loading. Due consideration must be made to ensure the cargo is loaded evenly in small piles in the first round. Subsequent passes can then be made to increase the cargo quantity of the piles in tandem.
This will ensure that cargo piles are spread out evenly which reduces the stresses on the vessel’s structure throughout the loading process. Similar planning is also required in the discharging process to eradicate undue stresses. When the principle of equal spreading is not followed, (as explained above) the vessel can experience either heavy hogging stresses (if the ends are loaded heavier than the midship section) or sagging stresses (if the midship section is loaded more than the ends) in the midship section, mainly concentrated in the areas of the hatchcoaming and bottom plating. This will cause deformation of the hatch coaming and, if excessive, can ultimately lead to hull failure and subsequent sinking of the barge.
Deformation of the hatch coaming is one of the tell-tale signs of a barge being subjected to excessive stresses. Although a barge may be certified to carry high density cargoes, it is important to remember that this carriage is always subject to the barge being operated within the parameters of the barge’s stability booklet at all times. To keep the barge safe a number of barge operators have adopted ‘additional strengthening’, in consultation with the Classification Society. This includes reinforcements in the areas of the hatch coaming, sheer strake and the longitudinal bulkhead from the tank top. This additional and approved strengthening may enable flexibility in the loading and discharging stages which, may in turn, aid a fast turnaround.
Similarly, while carrying project cargoes which cannot be spread across the holds, if the load is on the centreline, then the sagging stresses may be compensated by ballasting in the forward and aft parts of the holds. This can also be used with other bulk cargoes, such as sand. In order to avoid excessive transverse stresses when the heavy project cargo is to be loaded on the centreline of the vessel, transverse beams, wooden battens or thick steel plates may be spread across the full breadth of the hold and the cargo may be loaded on to it.
Once a safe cargo plan has been produced, it is important to ensure that cargo operations are conducted in accordance with the plan. A Member’s representative (loading supervisor) or the tug master (as applicable) should monitor the loading/discharging operations and stop the job if the barge is being incorrectly loaded or discharged. Crew and loading supervisors should be explicitly given authority to enable them to feel empowered to stop any unsafe operation. There should also be a system in place for these events to be reported back to shore management.
We recommend that Members operating inland barges ensure that cargo operations are planned and carried out in consultation with the barge’s stability booklets. Additionally, the Club has produced a booklet on ‘Basic stability for small vessels’ which gives guidance on the fundamentals of stability.
We thank BMT Surveys (Antwerp) NV and ConsulMar S.R.L (Argentina) for their valuable contributions to this bulletin.
Figs. 1&2 Hull failure due to uneven distribution of cargo (sagging).