Deterioration of ships hull / structure through corrosion, fatigue and damage is identified as a principal factor in the loss of many ships carrying cargo in bulk. The cargoes under scanner being the coal and iron ore. There are these two things which happen here.
(i) Failing to identify such deterioration; and
(ii) sudden unexpected accident.
Bulk carrier crew may be unaware of the vulnerability of these vessel types. The consequential loss of a ship carrying heavy cargo can be very rapid and possibly mysterious.
1. The Hull Stress Monitors employed on board help. These include sensors, accelerometers and a central computer. Sensors also known as strain gauges, fitted at various locations on the vessel’s deck to sense stresses during loading, discharging and at sea. One accelerometer is fitted at the bow to measure the vertical acceleration of the bow, and two fitted on the centreline to measure the roll and swing of the vessel.
The HSMS information is fed into a central computer and the information is normally provided in the cargo office and on the bridge. If the stresses reach a predetermined stress level, an audio visual alarm sounds to warn the operators.
This means that ship’s personnel can use the HSMS at sea to select a better course or speed, if the ship is subjected to heavy stresses, and also during loading and discharging operations if loads are exceeded.
2. Appropriate corrosion prevention methods are incorporated into the initial design of a vessel. These include the use of cathodic protection systems and various types of protective paint coatings. Areas with excessive coating breakdown and/or wastage are then replaced or repaired.
3. Risk Assessment is a useful tool for bulk carriers. To overcome the problems associated with operational factors such as stresses during loading and discharging, the ship’s officers should prepare and plan a sequence for loading / discharging and deballasting / ballasting. Contingencies should be planned by identifying hazards and carrying out and documenting risk assessments. The control measures identified in risk assessments should be closely monitored. A thin layer of high density cargoes or a layer of dunnage should be spread on the tank top before fixing the loader in a central position within the hold. This will help protect the tank top from damage.
4. There must be regular inspection of the cargo hold by ship’s personnel.
Findings by the ship’s officers should be reported to the owner immediately so that a subsequent detailed inspection may be carried out by expert surveyors and repairs effected as necessary, if possible when cargo discharging is complete. A close inspection should be made for any damage to the structure of the ship and the coatings caused by stevedores.
Operation of grab can cause serious damage to frames on shell, DB, air pipes, etc. The pneumatic hammers and caterpillars have been known to cause damage to hopper tanks and ladders. These damages are directly related to seaworthiness and safety. Instructions must be given and effective action must be taken to prevent damaging activities in holds. Often pneumatic hammers are used to release bulk cargo clung to beams and inaccessible places and referred to as safe and usual practice for the particular cargo. Charterparty terms must be carefully read before agreeing to any condition.
The grabs when lowered at speed can puncture the tanktop. Irratic operation of grab can be dangerous to gear and jeopardize the safety too. The risk of puncturing of tank top is maximum when grab lands on bare metal with speed. The risk is there even when one part of grab lands on cargo & other on bare metal with speed.
5. Progressive flooding in the forward region may trigger the process of loss. Bilge well high water level alarms in all cargo holds, or in conveyor tunnels, as appropriate, giving an audible and visual alarm on the navigation bridge and cargo control room can give warning of ingress of sea water and should be dealt with promptly. When it occurs or is likely to occur, Masters should quickly assess damage to their ships by being alert to water ingress and its consequences.
6. On any ship, the pulse of ship must be felt. Indication of unusual motion or attitude of bulk carriers and risk management / evacuation
If a ship takes on an unusual trim or heel, or if her motions become changed, breach of the hull envelope should be suspected immediately: i) Unusual collections of water on decks may be indicating trim or heel abnormality. ii) Sudden changes of heel or trim will indicate flooding or in smaller ships with lighter cargoes it may indicate cargo shift.
Strengthening of Bulk Carriers
- The structural weaknesses of single side configuration results from the presence of the high rigidity of the wing tanks on top and hopper tank at bottom of the side structure. The tenderness of the sides and vulnerability of structure can be visualized by imagining a polythene bag having a metal frame at top and bottom, with the bag loaded with weight. Double hull structure arrangement is used to overcome the structural deficiency and weakness of single side configuration.
- The bulk cargo trade requires that the transverse bulkheads have lower and upper stools to improve loading and unloading of the bulk cargo and also to improve structural strength of transverse bulkheads.
- The stiffness and rigidity of stools may be increased when the ship is designed for carrying ore.
- All bulk carrier structures are strengthened by deep side girders in addition to a duct keel formed by two central girders in combination with longitudinal frames
- Rounded sheer strakes fitted in many ships provide additional strengthening.
- Frames fitted inside double bottoms and wing tanks provide a smooth surface within the cargo holds for ease of cargo discharge and hold cleaning. There is reduced clinging of cargo on a clean interior and hence less chances of damage.
- The transverse bulkheads are of corrugated construction.
Measures taken Internationally
Solas, 74 as amended:
Chapter XII, ‘Additional safety measures for bulk carriers’. In respect of bulk carriers constructed on or after 1 July 1999 and of 150 m in length and upwards of single side skin construction, designed to carry solid bulk cargoes having a density of 1,000 kg/m3 and above, shall have sufficient strength to withstand flooding of any one cargo hold in all loading and ballast conditions, taking also into account dynamic effects resulting from the presence of water in the hold, and taking into account the recommendations adopted by the Organization.
The bulk carriers constructed before 1 July 1999, of 150 m in length and upwards of single side skin construction, carrying solid bulk cargoes having a density of 1,780 kg/m3 and above, shall comply with this regulation in accordance with the implementation schedule specified in relevant regulation. The analysis of the losses of bulk carriers point fingers on the foremost hold. The transverse watertight bulkhead between the two foremost cargo holds and the double bottom of the foremost cargo hold shall have sufficient strength to withstand flooding of the foremost cargo hold, taking also into account dynamic effects resulting from the presence of water in the hold, in compliance with the bulk carrier bulkhead and double bottom strength standards. For the purpose of this regulation, the bulk carrier bulkhead and double bottom strength standards shall be treated as mandatory.
The following restrictions may be taken into account, (whenever solid bulk cargoes having a density of 1,780 kg/m3 and above are carried.):
1. restrictions on the distribution of the total cargo weight between the cargo holds; and
2. restrictions on the maximum deadweight.
Resolution A.713(17) emphasized the importance of regular inspections of bulk carriers, especially of older ships, and in 1993 guidelines on an enhanced programme of inspections during surveys of bulk carriers and oil tankers were adopted by the 18th Assembly by resolution A.744(18). It was originally intended that the guidelines would apply to tankers but because of concern about the loss of bulk carriers they were extended to them as well. The guidelines were regarded as so important to safety that amendments to SOLAS to make them mandatory were adopted in May 1994 and entered into force on 1 January 1996.
The guidelines apply to existing tankers and bulk carriers of five years of age and over which means that the vast majority of the world tankers and bulk carriers are affected. The enhanced surveys must be carried out during the periodical, intermediate and annual surveys prescribed by the SOLAS Convention. The enhanced survey programme is mandatory for oil tankers under Regulation 13G of Annex I to the International Convention for the Prevention of Pollution from Ships, 1973, as modified by the Protocol of 1978 relating thereto (MARPOL 73/78). The guidelines pay special attention to corrosion. Coatings and tank corrosion prevention systems must be thoroughly checked and measurements must also be carried out to check the thickness of plates. These measurements become more extensive as the ship ages. The guidelines go into detail to explain the extra checks that should be carried out during enhanced surveys. One section deals with preparations for surveys and another with the documentation which should be kept on board each ship and be readily available to surveyors. This should record full reports of all surveys carried out on the ship.
Annexes to the guidelines go into still more detail and are intended to assist implementation. They specify the structural members that should be examined, for example, in areas of extensive corrosion; outline procedures for certification of companies engaged in thickness measurement of hull structures; recommend procedures for thickness measurements and close-up surveys; and give guidance on preparing the documentation required.
Various IMO Resolutions:
An IMO resolution urges Governments to apply IACS recommendation on loading instruments when approving loading instruments as required by Regulation 11 of the new Chapter XII, and to ensure that loading instruments already fitted have been approved in accordance with the standards of recognized organizations.
Guidelines on early assessment of hull damage and possible need for abandonment of bulk carriers:
MSC/Circ.1143, dated 13th December 2004 titled ‘Guidelines on early assessment of hull damage and possible need for abandonment of bulk carriers’, is an informative tool in the normal and post damage management of a bulk carrier. The Maritime Safety Committee, at its seventy-sixth session (December 2002), considered recommendations for decision-making emanating from various formal safety assessment (FSA) studies on bulk carrier safety. In particular, the Committee agreed that a circular should be prepared addressing bulk carriers which may not withstand flooding of any one cargo hold and containing information on the action to be taken in case of flooding of such holds, making sure that the professional judgement of the Master is not undermined.
CSR for Bulk Carriers and Oil Tankers:
CSR for Bulk Carriers and Oil Tankers were adopted on 18th December 2013. They entered into force on 1st July 2015 and supersede Common Structural Rules for Double Hull Oil Tankers and Bulk Carriers, July 2012. These Common Structural Rules consist of two parts. Part One provides requirements common to both Double Hull Oil Tankers and Bulk Carriers and Part Two provides additional requirements applied to either Double Hull Oil Tankers or Bulk Carriers. They also comply with SOLAS II-1 Regulation 3-10, ‘Goal-based ship construction standards for bulk carriers and oil tankers’ (GBS).
Formal Safety Assessment:
FSA is a process for assessing the risks associated with any sphere of activity, and for evaluating the costs and benefits of different options for reducing those risks. It therefore enables, in its potential application to the rule making process, an objective assessment to be made of the need for, and content of, safety regulations. The FSA consists of five steps:
1. identification of hazards (with potential causes and outcomes);
2. assessment of risks (evaluation of risk factors);
3. risk control options (using the regulatory measures to control and reduce the identified risks);
4. cost benefit assessment; and
5. recommendations for decision-making (information about the hazards, their associated risks and the cost effectiveness of alternative risk control options is provided).
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