the shafting and bearings is not permanently fixed but
changes with every dry docking, in keel blocking, and
All of the propulsion shaft components we have
throughout temperature variations.
described demonstrate similar symptoms when a
The alignment of the struts and stern tubes must be
casualty occurs. These symptoms include unusual noise,
in relation to each other as well as to the main propulsion
excessive vibration, and overheating. Unusual noise and
machinery. These alignments will undergo a natural
excessive vibration can be especially tricky to detect,
change if the propeller, propeller shaft, LSBs, or all of
identify, and trace. That is why whenever you detect one
these parts are temporarily removed.
of these symptoms, it is extremely important that you
make a thorough inspection of all propulsion shafting
The temporary removal of any machinery attached
components. Let's take a closer look at each of these
to shafting, bearings, or their immediate surrounding
areas can redistribute weight and stresses in the system.
This can result in misalignment. Furthermore,
UNUSUAL NOISE. This symptom may be
alignment is not the same when the vessel is waterborne
accompanied by vibration and can have several causes.
Since the most common causes are already listed in the
as it is when the vessel is in dry dock. Remember, the
EOCC, we will keep our description brief.
final alignment and bolting up of the main propulsion
shafting of any vessel should always be done when the
If the sealing disc in a bulkhead seal begins to rotate
vessel is waterborne.
against the inside of the cover plate, a squeaking or
squealing noise will be produced. Another cause could
There is really only one component of the
be an object that has fallen or is improperly stowed
propulsion shafting to which you may have to perform
against the propulsion shaft. The type of noise can vary,
an adjustmentthe stern tube seal. There are only two
depending on the position of the object and the material
times when you should adjust this component: (1) when
from which it is made (cardboard, wood, or steel, for
the seal is leaking, and (2) when emergency packing
must be installed and you must compress the packing to
EXCESSIVE VIBRATION. Internal damage to
maintain a proper seal and leakage rate. Always take
one of the drive train components or propeller damage
special care when you are adjusting the seal seating
are the usual causes of this symptom. Broken or
pressure. If overcompression occurs, the seal will
damaged MRG teeth may cause internal damage. A
overheat. If the spring is undercompressed, the seal will
fouled or damaged (unbalanced) propeller blading can
also cause excessive vibration.
Removal and Replacement of Components
OVERHEATING. Of the three major symptoms,
this is the one you will encounter the most often. A lack
of lubrication, such as a low oil level in a LSB or
Believe it or not, there will be occasions when you
insufficient cooling water to the stem tube seal, is
will be required to remove and replace components on
normally the first thing you should check. If overheating
the propulsion shaft. There is one type of component that
becomes too severe, another symptom, such as unusual
is subject to failure and is installed in all of the
noise, may occur. That is why a quick response and
previously mentioned components-a seal. In the
proper identification of the casualty are so important.
following paragraphs, we will briefly discuss some of
the key points for seal removal and replacement.
Alignments and Adjustments
LINE SHAFT BEARINGS. The line shaft
The alignment or adjustment of the bulkhead and
bearings have a double sealing system in which there is
stern tube seals arc the only propulsion shaft
a combination of two seals installed at each end of the
components that shipboard personnel will normally be
bearing. All four seals are identical in design and can be
able to perform. If an IMA is making the repairs,
easily removed and replaced by the ship's company. An
shipboard personnel will be required for quality
important thing to remember, however, is that the
assurance inspections and in most cases called upon to
sealing lip of each seal must face in opposite directions,
help in the repair effort.
as shown in figure 5-7. The innermost seal faces inward
to keep the oil from leaking out of the bearing and the
If an alignment (or even checking the alignment) of
outer seal faces outward to keep water from entering the
the propulsion shaft is required, then a ship repair
bearing if the space becomes flooded.
facility must be called in. Remember, the alignment of