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Precautions to bulk carriers hull corrosion, metal fatigues & other operational factors
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.Solas Chapter XI-1, requires bulk carriers to comply with the enhanced survey programme (ESP) of inspections, including regular inspection of the cargo hold by ship's personnel. However, owing to the time constraints in port, ships' manning levels and charterers' requirements, it is recognised that this may not always be feasible.
The following precautions associated with ships structural problems need to be considered:
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. There are times during discharge when an impact caused by the grabs is heard and a tremor is felt through the ship. On such occasions, an inspection of the hold should take place. Areas particularly susceptible to damage include:
Fig:Cargo hold ladders in good condition
- pipe guards
- manhole and bilge covers
- hatch coamings
- compression bars
- ship's rails.
This damage can easily be identified and should be repaired before departure. Officers observing such damage should immediately put the foreman on notice of their obligation to repair the damage. A stevedore damage report form should be completed.
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 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.
Typical bulk carrier cross section
Fig: Watertight hatch covers on bulk carrier
Strengthening of Bulk Carriers
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. Some bulk carriers may be fitted with longitudinal bulkheads for additional strengthening as well as for division of cargo compartments. Rounded sheer strakes fitted in many ships provide additional strengthening, and the frames fitted inside double bottoms and wing tanks provide a smooth surface within the cargo holds for ease of cargo discharge and hold cleaning. The transverse bulkheads are of corrugated construction.
Double hull bulk carrier cross section
High Tensile Steel (HTS) is commonly used in bulk carriers to reduce the thickness of the structure, increasing cargo carrying capacity. However, the downside of HTS is that, when any structure is corroded, the loss of strength occurs far quicker than for mild steel. Therefore, high notch tough steel is used in crucial areas such as the keel, bilge, deck stringer, sheer strakes and top/bottom parts of bulkheads to provide continual strength throughout the vessel's life.
Structural Standards for Bulk Carriers
Bulk carriers are known to be more susceptible to structural failure than other similar sized ships, particularly when a hull breach causes water ingress into the cargo holds. The primary precaution however is still to vigilantly monitor the structure for any signs of deformation, fatigue or corrosion and apply preventive rather than reactive maintenance. Cargo operations should be carried out carefully, to ensure sufficient stability throughout the passage.
However, despite all these precautions, incidents on bulk carriers causing loss of both life and cargo have caused concern from the 1980s, leading to the development of new structural standards for bulk carriers.
High rate of corrosion at sea and preventing methods
Structural strength requirements for mechanical steel hatch covers
Ships structural problem because of corrosion & metal fatigues - related countermeasures
Classification Society Establishes Design Standards For Bulk Carriers
Our detail pages illustrated many safety aspects of Bulk carrier
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- Indication of unusual motion or attitude of bulk carriers and risk management / evacuation
- Deterioration of ships structure and consequences of forward flooding
- Handling water ingress problems in bulk carrier, investigation and countermeasures
- Survival and safety procedure for bulk carriers
- Hatch cover strength requirement for a seagoing bulk carrier
- Ships longitudinal subdivisions - use of transverse watertight bulkheads
- Suitability of Shore Terminals for handling bulk cargo
- Preparation for ships carrying bulk cargo & standard loading condition
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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