Page 222 - Introduction to Marine Engineering

Shafting and propellers 203

Where the thrust shaft is an integral part of the engine, the casing is
usually fabricated in a similar manner to the engine bedplate to which it
is bolted. Pressurised lubrication from the engine lubricating oil system
is provided and most other details of construction are similar to the
independent type of thrust block.

Shaft bearings

Shaft bearings are of two types, the aftermost tunnel bearing and all
others. The aftermost tunnel bearing has a top and bottom bearing shell
because it must counteract the propeller mass and take a vertical upward
thrust at the forward end of the tailshaft. The other shaft bearings only
support the shaft weight and thus have only lower half bearing shells.
An intermediate tunnel bearing is shown in Figure 11.3. The usual
journal bush is here replaced by pivoting pads. The tilting pad is better
able to carry high overloads and retain a thick oil lubrication film.
Lubrication is from a bath in the lower half of the casing, and an oil
thrower ring dips into the oil and carries it round the shaft as it rotates.
Cooling of the bearing is by water circulating through a tube cooler in
the bottom of the casing.

Figure 11.3 Tunnel bearing