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Deterioration of bulk carriers hull and consequences of hull damage /forward flooding
Hull damage : 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 . Failing to identify such deterioration may lead to sudden and unexpected accident. Bulk carrier crews may be unaware of the vulnerability of these vessel types. The consequential loss of a ship carrying heavy cargo can be expected to be very rapid, should a major failure occur.
Progressive flooding in the forward region
Spaces forward of the collision bulkhead will, in the event of flooding, significantly affect the trim of the ship and reduce freeboard at the bow. In rough weather condition this further threatens the ship as open seas come inboard and impact on hatch covers and other fittings that protect the water or weathertight integrity of the ship. Hull plating in the region of the bow protects the fore peak tank and other spaces as do air pipes and ventilators. If any of them are damaged the ship's ability to resist further escalation of flooding is compromised.
Fig: Structural failure and flooding of bulk carrier
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 ingrss 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.
The following guidelines are given to assist them in this assessment.
Measuring cargo temperature
Temperature of cargoes like coal and grains should be regularly checked in order to detect signs of heating. Temperature should be obtained by lowering a thermometer into the sounding pipes on the port and starboard sides at the after end of each hold.
An additional temperature pipe should be sited beside the hold ladder at the fore end of the hold. A thermometer for each position should be placed at a designated place and withdrawn immediately when readings are required.
The most accurate and reliable readings can be obtained by making sure that the thermometers are lowered to a level, which is well below the surface of the cargo, and that they are left in position for several minutes.
Where possible there should be a thermometer for each position and thermometers should be left in place permanently and withdrawn rapidly when readings are required. Mercury thermometers are considered to be less satisfactory for taking cargo temperatures unless fitted with a maximum temperature indicator and reset before the taking of each reading, and one authority recommends the use of suitably calibrated pyrometers.
When carrying coal it is necessary to test the air in the holds for hazardous gases. If the cargo was fumigated before departure from the loading port and if fumigation is continued in transit, regular checks should be made for leakage of the fumigant for so long as it remains active.
Bulk carrier losses in the early 1990s were dramatic: ships sank rapidly, often with the loss of all lives. Many were old and had suffered structural damage. A study by IACS (International Association of Classification Societies) found that after flooding in the foremost hold, the bulkhead between this hold and the adjacent hold can collapse from the pressure of cargo and water, leading to progressive flooding and sinking.
Indication of unusual motion or attitude of bulk carriers and risk management / evacuation
Handling water ingress problems in bulk carrier, investigation and countermeasures
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.
Areas of bulk carrier likely to fracture
Based on experience of accidents with lesser consequences it was concluded that the casualties occurred through local structural failure leading to loss of watertight integrity of the side shell followed by progressive flooding through damaged bulkheads. Any prudent Master may wish to investigate any suspected water ingress more closely but preparations for evacuating the ship should be made instantly and concurrent with any investigation.
Survival and safety procedure for bulk carriers
Particular emphasis has been placed on being ready for early evacuation or abandonment of the vessel. For ships carrying high-density cargoes this is of importance while they are at sea. There may however be cases where abandonment may be the worst option and for bulk carriers as with other ship types this is most probably true in the event of grounding.
Damage investigation and countermeasures for bulk carriers
Damage to side shell, externally through contact with docksides or tugs and, internally from impact by cargo dislodging equipment during discharge, can result in initiating fractures and/or fatigue of the structure. In single side-skin bulk carriers, bulkheads, trunks and ballast tank boundaries, can present "hard spots" that concentrate forces where the change in construction occurs (e.g. longitudinal to transverse framing). This may lead to undetected fractures.
Structural standards & strengthening of bulk carriers
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 . Failing to identify such deterioration may lead to sudden and unexpected accident. Bulk carrier crews may be unaware of the vulnerability of these vessel types. The consequential loss of a ship carrying heavy cargo can be expected to be very rapid, should a major failure occur.
Monitoring hull stresses during rough sea conditions
The stresses upon the structure of bulk carriers are at their extreme limit in heavy seas; this is the time when most bulk carrier losses have been recorded. The IMO, therefore, recommended fitting hull stress monitoring systems on bulk carriers over 20,000 tonnes to minimise the dangers associated with longitudinal stresses due to vessels bending and pitching in a seaway and possibly triggering fatigue failure and above.
Our detail pages illustrated many safety aspects of Bulk carrier
- Structural problems associated with corrosion, metal fatigues & other operational factors
- Local loading criteria defining maximum allowable cargo weight in each cargo hold
- Ships Confined area safe practice
- Handling water ingress problems in bulk carrier, investigation and countermeasures
- Survival and safety procedure for bulk carriers
- Shearing forces & bending moments limitations in bulk carriers
- Risk of Heavy cargoes & Monitoring the Ship's Loading limits
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Operation of sea going bulk carriers involved numerous hazards . Careful planning and exercising due caution for all critical shipboard matters are important . This site is a quick reference to international shipping community with guidance and information on the loading and discharging of modern bulk carriers so as to remain within the limitations as specified by the classification society.
It is vital to reduce the likelihood of over-stressing the ship's structure and also complying with all essential safety measures for a safe passage at sea. Our detail pages contain various bulk carrier related topics that might be useful for people working on board and those who working ashore in the terminal. For any remarks please Contact us
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