Tank Vessel Design Considerations:
Major design and construction changes since World War II have generally increased the potential pollution hazard, resulting from individual cases of collision and stranding. These have to be checked.
Governmental and Regulatory Body Recommendations Considerable private and public activity, following the Torrey Canyon incident, has been aimed at establishing the Marine Safety Committee.
Maneuverability should be very high to avoid collision and grounding in emergency conditions.
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Backing Power Steam turbine propelled, single screw U.S. flag tankers with displacements ranging from 25000 to 77000 tons can be expected to stop 81/2 to 9 ship lengths from the full ahead condition.
Further, periods of 51/2 to 9 minutes will be required to execute this manoeuvre, from the time the crash stop order is given. By contrast, the 144,000 dwt. combination oil/bulk vessel Cedros required 10 ship lengths and over 11 minutes to stop from an initial speed of 18 knots.
Steering and Directional Control In view of the greatly increased sizes and relatively reduced installed power of large tankers, the following suggestions are offered:
Establishment of minimum standards of control, including the turning rate ; the turning cycles should be determined by standardized trial procedures.
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Study of Rudder design -current standard horn type rudders or conventional, closed stern, fair form rudders should be changed in order to improve characteristics at high rudder angles and at low manoeuvring speeds.
The various configurations that might be improved, after study, include active rudders, biplane and triplane rudders, flapped rudders and Kort Nozzle rudders. Various bow and stern thruster systems have been developed, some well over 1000 hp in size that can also be applied to tankers to improve the steering system.
Collision Protection A structural, shock absorbing barrier at the ship side, in way of cargo tanks should be provided. This outer space, while lost to cargo capacity, is available for clean ballast. The conventional port and starboat wing bulkheads can be located well outboard.
Mooring Gear and Ground Tackle A last resort to stop the ship, and normal tool for low speed manoeuvring, is the use of ships anchors. Hence, there should be means for more rapid release of anchor and chain. Centralized control of the mooring gears, from the bridge, is an improvement in this direction.
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Cargo Contaminant in the Event of Collision and Grounding Tank compartments should be smaller and more in number. Inflammable or other types of oil booms should be
carried by ships. Chemical detergents and other dispersal systems should also be carried on ships. A foamed plastic system should be available to seal off small ruptures in cargo tanks.
Radical Solutions On a global basis, serious consideration has been given to the following possibilities to limit the pollution hazard:
1. Reorganization of oil tanker operations to routes remote from populated areas or on comparatively lightly travelled ocean lines.
2. Adoption of costly navigation and/ or inertial guidance systems to insure a higher precision in the control of ship routes.
3. Use of submarine tankers, to reduce the probability of ship collisions. The hazards of grounding are, of course, increased.
4. Accelerated development of long distance oil pipelines as a substitute for tank vessels.
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Off-Shore Production:
Offshore oil wells and drilling operations are required to have such features as blowout preventers, storm chocks, fire preventer equipments and aids to navigation.
Control of Oil spillage:
The potential of aerial photography and more especially infrared, ultraviolet and microwave imagery in surveillance and oil slick detection should be evaluated in detail.
Microwave, having all weather capabilities, should be used first; then, processed information may be used on ultraviolet and infrared photography.
FM-C W radar has a similar all weather capability, but microwaves are preferable.
Actual reconnaissance techniques are also useful for tracing surface buoys, which could be released near the oil spill, to determine the rates of surface currents. A combination of photographic, ultraviolet, infrared and microwave techniques should be used.
Prediction of Oil Slick Behaviour The behaviour and rate of movement of oil slicks on water are rather poorly understood despite the importance of deploying defensive measures. Transport and dissipation are two pertinent problems.
The direction and speed of an oil slick yields more to wind than the influence of ocean currents. This is because of the greater momentum given to the oil slick by the wind.
Water currents that are near the surface, which are under the influence of wind, are expected to follow the mathematical representation of the Econ spiral. The wind created currents, thus, flow slightly to the right of the wind direction in the Northern hemisphere.
Mechanically and thermally induced ocean currents, e.g., Gulf Stream, which would affect the motion of an oil slick as well. As oil slick approaches a land mass, a variation in its motion is also expected.
Chemical Treatment, Absorption and Sinking Agents There are numerous compounds and materials available to collect or sink oil slicks. Four types of collecting agents have been identified and suggested for oil slick recovery. These are
1. Floating absorbents such as straw and saw dust.
2. Plastic or other polymeric material such as polyurethane foam
3. Gelling agents.
4. Demulsifiers.
Gelling agents that can solidify petroleum materials are in developmental stage and may
Numerous solid absorptions for sinking oil are also available, though the weight of material required, per unit of oil, and the attendant logistic problems present practical difficulties. Demersal fish species may be adversely affected and a resurfacing of the oil mass is also generally probable, although it is delayed and slow.
The majority opinion is against the use of these dispersants and demulsifiers, because they are toxic to aquatic life in general.
Biological Degradation of Crude Oil and Oilfraction in Oceans. Biological degradation of hydrocarbons in the ocean could be carried out using suitable species of microbio’a. Although degradation will take place in the ocean, and is, in fact, the ultimate fate of oil, the rates are very slow.
Confining Spills:
The ability to confine a spill, in the area immediately surrounding the source, is principally dependent on the availability of equipment and the prevailing environmental conditions. An incident, that essentially open an entire vessel to the sea, would involve rapid spreading of oil and, therefore, the equipment must be ready for use immediately.
Floating Booms and Underwater Bubble Barriers Both these are presently suitable for relatively calm water and are subject to failure. The floating booms are, generally, superior to bubble barriers in an emergency because they are more portable and involve less erection time.
The main advantage of the bubble barrier is the unrestricted entry and exit of ship it allow s while the main disadvantage is the complete loss of containment in the event of air supply failure.
Burning the ability to destroy cargo on site depends largely on the nature and quantity of the cargo. If all attempts to salvage a vessel or cargo have failed and a ship has been abandoned, an attempt should be made to set the oil afire while it is still contained within the vessel.
Controlled demolition techniques may be applicable to opening the vessel without allowing oil to escape while providing access to air. Mixing kerosene or other highly flammable material with crude of heavy oil cargo would greatly enhance the burning.
Skimming Mechanical devices for collecting oil from the surface of the water such as rotating cylinders and suction pumps are used.