Figure 5-6.-Cutaway view of a typical bulkhead seal.
required air pressure. Next, you should check the
sealing disc is a good indication that you have a few
seawater cooling system. Check both the ship's
weak compression springs that have allowed the disc
seawater cooling system, which provides cooling
to rotate with the shaft.
seawater during normal operations, and the firemain
system, which provides emergency cooling seawater,
Another key point to look for is signs of wear on
for proper pressure and flow. If a seawater strainer is
the buffers installed on the bottom of the sealing
included in your ship's seawater cooling system,
discs. If you detect wear and the pattern of wear is
check it also and clean it as required. Then, you
not uniform, then the shaft to bulkhead seal
should check the stem tube seal itself for leakage.
alignment is most likely incorrect.
Even though the sealing assembly is mechanical, you
can adjust the spring pressure to maintain a proper
STERN TUBE SEALS. Your inspection of an
seal. We will explain this adjustment procedure later
individual stem tube seal should consist of the seal
in this chapter.
and its support systems. There are two support
systems you should check: (1) the seawater service
MAIN THRUST BEARING. The main thrust
system, which provides cooling; and (2) the ship's
bearing will normally be inspected as frequently as
service air system, which provides the air for seal
the MRG when the propulsion plant is in operation.
During a normal inspection, you should check for the
proper oil flow and oil temperature and for leakage.
You should check both subsystems for proper
You should also periodically inspect the main thrust
operation as they pertain to the operation of the stern
bearing according to the PMS for excessive thrust.
tube seals. For example, you should check the
Like the LSB, you should use a depth micrometer to
inflatable seal operation at least every 6 months.
measure the thrust. Normally, the measurement plug
Remember, the proper operation of the inflatable seal
is located on the propulsion shaft side of the MRG
is crucial to safety and your ship's ability to survive.
casing. By moving the shaft first in the ahead and
Check both the ship's service air system, which
then in the astern direction, you can measure the
provides air pressure under normal operation
actual movement of the second reduction gear (bull
conditions, and the compressed air bottles, which
gear). Use these readings in the same reamer as you
supply emergency air pressure to the seals, to make
would the thrust readings for a LSB.
certain the inflatable seal is always supplied with the