discharge position. Ensure that the gagged scupper
CHT SYSTEM OPERATIONAL MODES
valves near the overboard discharge are open.
There are three operating modes for the CHT
2. Open the pump suction valves (A) and the
system: at-sea, transit, and in-port. The at-sea
pump discharge valves (B).
mode is used when the ship is outside the 3-mile
limit, known as the contiguous zone. In this mode,
3. Shift the pump discharge diverter valve (C)
the valve alignment allows both the soil and the
to the overboard discharge position.
waste drains to be diverted directly overboard. The
transit mode is used just before the sewage transfer
4. Set the discharge pump controller selector
hoses are disconnected and while the ship is
switches to the MAN 1 position.
underway within the 3-mile limit, known as the
restricted zone. The valve alignment for the transit
5. After the pumps lose suction, set both
mode requires the soil drains to be diverted to the
controller selector switches to the AUTO position.
holding tank and the waste drains to be diverted
overboard. The in-port mode is used whenever the
6. Open the tank washdown supply valve (L)
ship is pierside. In this mode, the valve alignment
and wash the tank for 30 minutes.
diverts both the soil and the waste drains to the
holding tank. The discharge piping is aligned to the
deck risers where the sewage transfer hoses are
7. Close the tank washdown supply valve (L).
connected to the ship's system and the pier's system.
The pumps are set in the automatic mode to
8. Set the controller selector switches to the
MAN 1 position.
discharge the sewage off the ship to the pier. When
ships are on extended cruises, the CHT system
9. After loss of pump suction, set the controller
should be exercised in all modes at least once each
switches in the OFF position.
week. This will allow you to flush the tank weekly
as required and, by doing so, keep toxic gases to a
minimum.
You should check each mode of
10. Close the pump suction valves (A) and the
operation weekly. This will ensure that the valves
pump discharge valves (B).
operate smoothly and do not leak. Any leaks must
be corrected immediately.
11. For the strainer-type CHT system, close the
inflow stop valves (G). For the comminutor-type
The Sewage Disposal Operational Sequencing
CHT system, secure the comminutor isolationvalves
S y s t e m (SDOSS) was designed using the
(D) right after shifting the soil drain diverter valves
Engineering Operational Sequencing System
(H) to the overboard position. For comminutor
( E O S S ) as a guideline. The SDOSS gives
systems with the aeration system, close the air
blower discharge valve (M) and secure the air
step-by-step procedures for changing the valve
alignment when changing the operational mode of
blower. Or, secure the ship's service air system
the system. It also gives step-by-step procedures for
supply valves (N) once the tank washdown
other operations of the system, such as cleaning the
procedures have been completed and the pump has
tank. Refer to the foldouts of figures 17-1, 17-2,
lost suction. If an air aspirator system is installed,
and 17-3 for the location of drains, valves, and other
shut down the system and secure the aspiration
components as we continue the discussion on the
pump.
various modes of operation.
After you have placed the valve alignment in the
At-Sea Mode
at-sea mode, place the electrical components in the
at-sea mode as follows:
Once the ship is beyond the 3-mile limit, and in
the area known as the contiguous zone, the CHT
1. De-energize the controller at the local power
system may be placed in the at-sea mode by
panel by placing the pump controller selector
following these procedures:
switches in the OFF position.
1. Place the soil drain diverter valve (H) and
2. Place the local CHT holding tank high-level
the waste drain diverter valve (J) in the overboard
alarm cutout switch in the ON position. You can
then monitor the tank level for overfilling.
17-11