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Tankers move large bulk petroleum cargo with speed and safety. Petroleum base terminals should be able to receive tankers that are at least 600 feet long with a draft of 35 feet. Tankers and their equipment are described below.
Most of a tanker hull is used to carry liquid cargo. Cargo space varies among different types of tankers. Cargo space is divided into tank compartments by bulkheads which run the length and width of the tanker. The tank compartment is usually separated from fore and aft sections of the tanker by narrow, empty, liquid-tight compartments called cofferdams. Each tank compartment has a hatch and liquid-tight hatch cover. An-ullage sounding hole with a hinged cover is usually in each hatch cover. Tank compartments may have heating coils for heating cargo of heavy oil to viscosities suitable for pumping.
Vent lines are usually between each tank and hatch. At the hatch, the vent lines connect to headers. The headers extend up the masts and have flame arresters at the top. Vapors caused by agitation or high temperature of product are vented through these lines. Each vent line is fitted with a vacuum relief valve. When vapors condense in the tank because of low temperature, the relief valve permits intake of air to relieve any vacuum created.
Pipeline and Pumping Systems
A complex cargo line system controls product flow during loading and discharging and while the vessel is under way. Tank farm pumps or booster pumps are normally used to load tankers. Tankers usually have cargo pumps for pumping cargo ashore through the pipeline. Some tankers also have stripping systems used to strip the tanks dry of ballast.
Tanker fire-fighting equipment for the deck includes fire hoses, axes, buckets, and hand fire extinguishers. There may be a carbon dioxide fire extinguisher system for protecting fireroom bilges and electrical machinery. Most tankers also have a steam smothering system that can be used to fight fires. The main line of this system connects to the ship's auxiliary steam line through the master valve in the boiler room. It runs forward along the deck with a branch for each fuel and cargo tank and cofferdam. Branch lines also run to the forward holds, the pump room, and other areas.
Military liquid-cargo barges are steel watercraft. They move bulk petroleum products. Some are made for short distance hauls in harbor, coastal, or inland waters. Others are made for self delivery to an overseas destination and are self-sustaining for extended periods of operation. Barges have no propelling machinery; therefore, they require the services of a tug to move. A small tug is used for harbors and inland waterways while a large tug is used for coastal and intertheater missions.
Pumps and Piping Systems
Some barges require off-vessel equipment for discharging cargo, while other have their own equipment. Self-discharging vessels generally use electrically powered rotary pumps. The pumps are usually below the deck in the aft section or midship section. As a fire precaution, the pump room is completely insulated from the cargo and its gases. The piping systems on barges vary widely. There may be several pipelines, depending on the number of products carried. Vessels carrying light oils usually have pipelines with bellmouthed fittings. These fittings extend almost to the tank bottom. A stripper line, extending until it is almost flush with the tank bottom, is used to pump any oil left at the bottom of the tank. Vessels carrying heavy fuel oils and asphalts are usually equipped with 12- to 16-inch pumps and suitable pipelines.
Types of Barges
The military has 225-barrel-capacity and 4,160-barrel-capacity steel hull barges in its inventory. They are described below.
The 225-barrel Steel Barge
The barge (Figure 4-6) can carry limited quantities of liquid (225 barrels) or dry cargo (21 long tons) about harbors or inland waterways. Although this barge can carry limited quantities of liquid cargo, it does not have integral liquid-cargo pumps. It has an overall length of 45 feet 6 inches, an 18-foot 6-inch beam, and a molded depth of 3 feet. It has a displacement of 33 long tons loaded and a maximum draft of 1 foot 8 inches loaded. This barge consists of two sections joined end-to-end. The military has limited quantities of this barge remaining in its inventory. It is not considered a bulk transporter because of the limited capacity and the lack of integral pumping capability.
Figure 4-6. Steel barge with a 225-barrel or 21-ton capacity
The 4,160-Barrel Steel Barge
This barge (Figure 4-7) can carry 4,160 barrels of bulk liquid cargo or 578 long tons of dry cargo. The barge has an overall length of 120 feet, a 33-foot beam, and a molded depth of 10 feet 6 inches. It has an integral diesel-engine driven, liquid-cargo pump to receive and discharge liquid cargo.
Figure 4-7. Steel barge with a 4,160-barrel or 578-ton capacity
Sometimes tank barges are used for temporary storage of bulk petroleum products. However, the main uses for barges include the following:
§ Delivering fuel to and from shore terminals and moored oceangoing vessels which are limited by the depth of water.
§ Topping off partially loaded ocean tankers when docking the tanker would be too expensive or impossible because of the tide, wind, or depth of water.
§ Delivering bulk shipments of gasoline and lubricating oils in refueling operations at harbors and on rivers.
§ Removing oil sludge from the tanks of tankers and delivering it to shore tanks.
§ Moving petroleum products when it is cheaper to do so by water than by tank car.
Fire-fighting equipment for the deck includes fire hoses, axes, buckets, and hand fire extinguishers. Most vessels have fire pumps and carbon dioxide for fires below deck. Pressure and flow are controlled by a master valve. In case of fire, carbon dioxide is fed into the cargo tank to smother the flames. Some modern vessels have an inert gas system fitted to the liquid-cargo tanks. This system provides a positive gas pressure to the cargo tank. The gas is so deficient in oxygen that it renders the atmosphere in the liquid cargo tanks incapable of supporting combustion.
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