The double hull is usually trusted to provide a decrease in overall spill risk compared to single-hull tankers. However, double hulls do not warrant that no cargo will be spilled. The potential for a catastrophic oil spill from a double hull tanker is right, and the outcomes could be just as damaging as significant oil spills from single-hull carriers. Puzzles with double hull tanker design, construction, operation, and maintenance have been well documented over the last few decades.
Suggestions for improving double hull tanker safety include more significant repetition in new builds, compulsory minimum standards for the construction and renovation of vessels, and more stringent standards, oversight, and implementation by port states and classification societies. While significant attempts to address most of these issues are continuing, none can be accomplished overnight.
Even if all of the difficulties with double hull vessel designs are corrected in new vessel construction and operation, there are still a notable number of double-hull tankers already in operation that are exposed to failures and disasters. Therefore, policies and best management practices must be adopted and implemented to ensure that the seamen who operate these highly complicated vessels have the required training and expertise necessary to ensure safe operations.
Double hulls are a vital element of the oil spill prevention system, but they are not the only ingredient. The only way to safeguard upon the potential for ultimate oil spills from double-hull tankers is to create an effective prevention system that provides multi-layered against oil spills and accidents, including planning and human factor elements. Some industry recommended guidelines that might be useful for implementing oil pollution control onboard an oil tanker are summarized below.
Officers must understand the stability aspects of double-hull vessels.
Compared to conventional tankers, which are inherently stable, it is now recognized that double hull structures that do not have a centerline bulkhead have potential problems with large free surface effects. It may be encountered at various stages of cargo and ballast operations. As a consequence, a loss of GM may result in serious stability problems.
It must be emphasized that Masters and Officers must be fully aware of this potential problem and that all cargo and ballast operations are conducted strictly following the vessel’s approved loading manual. Changes to cargo plans must be thoroughly assessed before the revised plan is undertaken.
Guidelines For Prevention Of Oil Pollution Mitigation
The Gangway Watchman and the O.O.W. should periodically monitor the surface of the outboard sea to check for oil leakage and to try to detect such oil leakage (if any) early. O.O.W. should also follow the emission from the funnel stacks (excessive soot or sparks) and report abnormalities to the duty officer. If floating oil is observed on the surface of the sea in the vicinity of the vessel, it should be reported immediately to the officer on duty or the Chief Officer (whether the oil is originating from their ship or not). The officer on duty shall allocate a crew for periodic monitoring on deck and associated spaces.
The following are some examples of condition monitoring required: Which includes the conditions around the vessel, mooring ropes, and the surface of the outboard sea and the like. Also to detect any irregularity onboard and outboard the vessel.
oil pollution at sea
The officer on duty shall have the crew patrol or monitor the surface of the sea near the following places or outfit as required:-
Sea-chest (Cargo & Ballast)
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Overboard discharges,
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Floating hose,
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Stern tube,
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Shore connection, and
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Near SPM & SBM if applicable.
The company designated checklists should be used to ensure proper compliance of the above.
Action by Duty Officer
If the oil is observed on the water in the vicinity of the vessel and there is reason to suspect that the oil is originating from the ship, all cargo transfer operation shall be suspended, and the Master shall immediately be notified.
Appropriate notification following SOPEP/OPA90 and shall be executed. Immediate action should be taken to reduce such outflow (e.g., Depressurizing the system, Adjusting the level, etc.)
Plugging Deck Scupper Plugs
Suitable scupper plugs shall be used as the expansion-type oil-resistant rubber- mechanical scupper plug.
As a safety standard, the main deck scuppers should be further sealed with temporary putty after being fitted tightly in place. It is a further preventive measure, in case of improper surface/sealing of scupper opening.
The ship specific Scupper Checklist should be prepared & used for confirming the above.
Oil Coamings (e.g., save-all trays to air pipes serving oil tanks, mooring winch save-alls, etc.) shall be effectively plugged, and the ship specific Oil Coaming Plug Checklist should be prepared and used for confirming it.
If rainwater collects on the aft main deck, the rain may be released through the aftermost scuppers after carefully checking and confirming that No Oil-water or Traces of Oily sheen is mixed with the rainwater.
Such draining in port shall be carried out only after Loading Masters permission, bearing in mind the above.
Oil absorbent pads should be used as a precautionary measure when draining rainwater in port. Personnel shall continuously attend such operation and after completion, confirm with the C.O.C. the final status of scupper.
Also, if applicable, Siphon Line between the Main deck cargo area to the Accommodation area is to use for draining effectively.
However, if collected water is contaminated with oil, or if the terminal refuses to let the water through the scupper, then suitable means such as oil catcher (oil absorbent pads) to clear such oily sheen should be used to the satisfaction of the terminal representative.
Equipment Required For Oil Spill Detection -
Fixed Gas Detecting System
(Pump Room and Double Hull Spaces adjacent Cargo Tanks)
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Pump Room Bilge High Level Alarm
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Cargo Oil Pump, High Temperature Alarm & Trip System
(Casing / Bearing / Bulkhead of Pump Shaft)
Equipment for Oil Pollution Mitigation-
Deck Scupper Plugs with Higher Gutter Coaming on Main Deck
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Manifold Spill Tank
- Emergency Stop System of COP
- Emergency Shut Dow System of manifold Gate Valve
- Emergency Damper of Pump room Exhaust Fan
P & I Surveyor
When damage occurs to the property of a third party - for example, if a pipe fails during bunkering and oil is spilled into the harbor - the owner's P&I club will protect their interests in the ensuing investigation and clean up operation. When damage occurs, the owners or Master should alert the local P&I representative, who will instruct a surveyor to attend and assist. He will submit his report to the owners, and, if necessary, also arrange security with the club.
Oil Pollution Accident Handling Check List-
Notifying Everybody On Board:
Notifying the Master and make a post station announcement for Oil Spillage Decontamination.
Notify everybody to prohibit using fire (smoking, fire in the galley, etc.)
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Measures to Prevent Oil Overboard Discharge:
Confirm complete closure of scuppers. Open the emergency drain valve to cargo oil tanks (on Tankers).
Use of materials for oil removal (oil absorbent, sawdust, etc.)
- Initial Notification Report
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Confirming Conditions at the Scene:
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The source of oil spill. (If the oil flows out of damaged shell plates, the point of the
damage.)
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Type and quantity of oil outflow.
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The direction, speed and extent of the oil that has flowed outboard.
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Weather and sea conditions.
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Ship’s position, course and speed.
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The presence of casualties.
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Control the Discharge of Oil:
Carry out according to the “Shipboard Oil Pollution Emergency Plan,”
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Preparation of Necessary Documents
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Recording
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Record in a time series.
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Take pictures of the process of oil removal (Never use a flashbulb).
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Record items
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Weather, sea conditions, and tide (direction/speed).
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The source of oil spill.
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The direction, speed, extent and quantity of the oil that has flowed outboard.
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Actions taken for oil removal and materials used for removal and their quantity.
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The addresses, reported items and reporting methods used.
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Name of oil spill disposal companies, time of arrival and details of their work
(including those of the terminal side).
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Matters instructed by national or local authorities and details of the work done
according to such instruction.
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Ship’s position, course and speed.
If possible, collect a sample of the oil from sealing and keeping it on board.
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