The Cargo Oil System

The cargo oil system has the following functions: 

Filling cargo oil tanks. Fuel is received at the deck connections and flows to the cargo oil tanks through the suction/fill main. The cargo oil pumps are not used.

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Providing fuel to other ships. One or more cargo oil pumps take suction from cargo oil tanks through either the suction/fill main or the suction main. The pumps discharge through the discharge main to the deck connections.

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Transferring fuel between cargo oil tanks. A cargo oil pump takes suction from a cargo oil tank through the suction main. The pump discharges through either the discharge main or through the suction/fill main to another cargo oil tank.

CARGO OIL STRIPPING SYSTEM. Cargo oil stripping systems vary widely among ships. Most ships have two cargo oil stripping pumps installed in parallel. The cargo oil stripping system has the following functions: 

Stripping cargo oil tanks. A cargo oil stripping pump takes suction from a cargo oil tank and discharges to slack cargo oil tank, the settling tank, or to the contaminated cargo oil collecting tank.

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Stripping the cargo oil or settling tank or the contaminated cargo oil collecting tank. A cargo oil stripping pump takes suction from the tank being stripped. The discharge may then be sent to a number of different locations. The discharge may be sent overboard (where permitted), to the hose flushing main, to the main deck connections, to a slack cargo oil tank, to the settling tank, to the contaminated cargo oil collecting tank, or to the oily waste holding tank.

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Stripping cargo oil system piping. A hose can be attached to a fitting in the pump suction line and connected to a cargo oil system low-point drain to remove residual ballast water from the piping. A cargo oil stripping pump takes suction from the low-point drain through the hose, and discharges to any of the destinations listed in (b) above. S9086-SN-STM-010

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Transferring remaining fuel between cargo oil tanks. Because stripping tailpipes are lower in the tanks than cargo oil system tailpipes, the stripping system

can remove fuel remaining in a cargo oil tank when the cargo oil system loses suction. A cargo oil stripping pump takes suction from a cargo oil tank and discharges to the cargo oil system, which must be aligned to direct the fuel to the receiving cargo oil tank. STRIPPING SYSTEM. Water and sediment gradually accumulate at the bottom of service tanks and uncompensated storage tanks. When necessary, a stripping pump draws contaminated liquid from the tank bottoms and delivers it to a COST. The fuel stripping system is aligned to draw liquid from particular tanks as required. Usable fuel that rises to the top of the COST can be drawn off by a transfer pump. Stripping system configurations vary considerably. Gas turbine ships with seawater-compensated storage tanks have no separate stripping systems, but there are other ways to remove water and solid contaminants from fuel on these ships, such as service tank recirculation. CARGO OIL STRIPPING TAILPIPES. Cargo oil stripping tailpipes are lower in the cargo oil tanks than cargo oil system tailpipes, so the stripping system will draw off water and contaminants below the cargo oil system suction. All cargo oil stripping tailpipes are located on the same side of all tanks served, either port or starboard. This arrangement allows more fuel to be drawn from the tanks when necessary by listing the ship toward whichever side is appropriate. CARGO OIL SYSTEM FLOW RATES. Cargo oil pumps are typically centrifugal pumps of 3,000 gal/min capacity, although some pumps are rated as high as 6,000 gal/min. The flow rate of one 3,000-gal/min cargo oil pump matches that of one standard deck connection on a receiving ship. Tailpipes in larger cargo oil tanks can pass 3,000 gal/min. Wing tank tailpipes are usually limited to 1,500 gal/min. All cargo oil tank tailpipes on AOE 6 class ships can pass 3,000 gal/min. CARGO OIL SYSTEM PRESSURE REGULATION. The discharge pressure of motor-driven cargo

oil pumps is regulated by two independent valves. Both recirculate excess discharge fuel to cargo oil pump suction. Power-operated throttling valves are installed between the discharge risers and the suction/fill and suction mains. Pressure-regulating valves are installed at each pump to recirculate flow directly from pump discharge to pump suction to maintain discharge pressure below 150 lb/in2.