Figure 4-5.--Typical gas turbine FO tank level indicator
system.
are used solely for FO storage and management.
Tanks used for ballast are so designated and can
Figure 4-4.--Piping diagram of a DD-class ship fill and
be filled with seawater for ship stability and trim.
transfer header.
Some ship classes, such as the FFG, have a
modified clean ballast system. Designated FO
and is discharged overboard through an overflow
tanks can be ballasted with seawater through this
line from the overflow expansion tank.
system whenever the total FO load is reduced
When FO is taken from the storage tanks for
below a set percentage and additional ballast is
ship's use on gas turbine ships, seawater from the
required.
fire main provides a positive head on the system
The rated full capacity of a FO tank is
to the suction side of the transfer pump. Seawater
95 percent of the total capacity. The rated full
replaces the FO in the tanks and maintains the
capacity is computed after allowance has been
proper ship's trim.
made for all obstructions in the compartment. The
remaining 5 percent of the total tank capacity is
reserved to allow for FO expansion. Accordingly,
CAUTION
when FO is received, tanks should not be filled
beyond their rated capacity. This filling require-
Because of the danger of overpressu-
ment does not apply to ships having seawater
rizing the ship's receiving system during
compensating systems since these tanks are
refueling, maintain extremely close liaison
always 100 percent full. Expansion tanks are
between the receiving ship and the supply
provided on the CG-, and DD-class
ship relative to flow rates and line pressure.
ships to provide for FO expansion caused by
Means for throttling flow to each tank
temperature changes.
bank is provided to prevent tank over-
An electric level indicator with a magnetic
float (fig. 4-5) is used for FO tanks on gas
pressurization by use of the throttling
valve. Keep a close watch on liquid levels
turbine ships. It is replacing the pneumatic-type
and receiving tank pressures of banks
systems on ships with water-compensating systems
being filled on ships with compensating
because of its improved reliability and accuracy.
systems.
The Navy Oil Pollution Abatement Program
requires installation of a magnetic-float level
The clean ballast system provides complete
indicator with a high-level alarm in all FO tanks
that overflow directly overboard.
separation between the ship's FO storage tanks
and the seawater ballast system. Tanks designated
This type of indicator has a magnetic float,
transmitter (or sensor), and primary and
for FO storage are used for this purpose only. Fuel
fill, transfer, and stripping systems are isolated
secondary receivers (meters). The transmitter stem
4-13