ENGINEMAN 1 & C
Figure 4-5.Details of underwater strut bearing. A. Longitudinal view. B. Cross-sectional view. C. Rubber stripping in the
box. This permits the addition of a ring of new
packing, when needed, while the ship is water-
borne. Either braided flax packing or special
semimetallic packing must be used (ships
engineering drawings show the proper type of
packing). This gland is usually tightened to
eliminate leakage when the ship is in port, and
is loosened (prior to warming up) just enough to
permit a slight trickle of water for cooling pur-
poses when the ship is underway.
More recent shaft seal designs utilize packing
only for emergencies. These newer seals are of two
types; rubber face seals and mechanical face seals.
Both face seals are on a plane perpendicular to
the shafting, against a gland ring for rubber face
seal or against a seal ring for a mechanical face
seal. Further, most face seals require seawater for
both cooling and lubrication.
The rubber face consists of a rubber element
that is clamped around the shaft just tightly
enough to prevent rotational slippage and leakage
underneath the seal, while at the same time, the
seal is able to travel axially along the shaft. This
axial motion is necessary so that the seal can main-
tain its position against the gland ring regardless
of shaft position.