The CHT system accepts soil drains from water
closets and urinals, and waste drains from showers,
laundries, and galleys. The three functional elements of
sewage collection, holding, and transfer make up the
The collection element consists of soil and waste
drains with diverter valves. Depending on the position
of the diverter valves, the soil or waste can be diverted
overboard or into the CHT tank
The holding element consists of a holding tank. The
transfer element includes sewage pumps, overboard
and deck discharge piping, and deck discharge fittings.
The CHT system can be used in any of three distinct
modes of operation, depending on the situation.
1. When the ship passes through restricted zones,
the CHT system is set up to collect and hold the
discharges from the soil drains only.
2. During in-port periods, the CHT system will
collect, hold, and transfer to a shore sewage facility all
discharges from the soil and waste drains.
3. When the ship operates at sea outside restricted
areas, the CHT system will be set up to divert discharges
from soil and waste drains overboard.
The Naval Ships Technical Manual, chapter 593,
has more information on the operation and maintenance
of CHT systems.
FUEL OIL STORAGE AND HANDLING
Fuel oil systems aboard ship include fuel oil tanks,
fuel oil piping, fuel oil pumps, and the equipment we
use to strain, measure, and burn the fuel oil.
FUEL OIL TANKS
Navy ships use four kinds of tanks that are part of
the ships system to receive, hold, and distribute fuel oil.
They are (1) storage tanks, (2) overflow tanks, (3)
service tanks, and (4) contaminated oil settling tanks.
Well explain their functions in the following pages.
Fuel oil tanks are vented to the atmosphere through
pipes leading from the top of each tank to a location
abovedecks. The vent pipes allow air to leave or enter
the tank as fuel is added or removed. Most fuel oil tanks
are equipped with manholes, overflow lines, sounding
tubes, liquid level indicators, and lines by which you
may fill, empty, and cross-connect the tanks.
Fuel Oil Storage Tanks
The main fuel oil storage tanks are part of the ships
structure. They may be located forward and aft of the
machinery spaces or abreast of these spaces. They may
be in double-bottom compartments as long as those
compartments are not directly under boilers. Some
tanks have connections that allow them to be filled with
fuel oil or with seawater from the ballasting system.
Fuel Oil Overflow Tanks
Fuel oil overflow tanks receive the overflow from
fuel oil storage tanks that are not fitted with independent
overboard overflows. Overflow tanks also serve as
ballast tanks because they can be filled with seawater
from the ballasting system.
Fuel Oil Service Tanks
Fuel oil is taken aboard by fueling trunks or special
connections leading to the fuel oil storage tanks. The
fuel oil is then pumped to the fuel oil service tanks. All
fuel for immediate use is drawn from the service tanks.
The fuel oil service tanks are considered part of the fuel
oil service system described later in this section.
Contaminated Oil Settling Tanks
The contaminated oil settling tanks hold oil that is
contaminated with water or other impurities. After the
oil has settled, the unburnable material, such as water
and sludge, is pumped out through low suction
connections. The burnable oil remaining in the tanks is
transferred to a storage tank or a service tank.
The contaminated oil tanks also can receive and
store oil, or oily water, until it can be discharged
overboard without violation of environmental
regulations. See OPNAVINST 5090.1 to learn when
you may empty the contaminated oil settling tanks
either overboard or to barges.
FUEL OIL PIPING SYSTEM
The fuel oil piping system includes the piping and
pumps for three systems, each of which is connected at
different levels of the storage or service tanks for (1) the
fuel oil filling and transfer system, (2) the fuel oil
service system, and (3) the fuel oil tank stripping
system. The pipes are connected to the storage and
service tanks at different levels so the pumps can take
suction from any of these levels. The service system is
connected at the highest level, the filling and transfer