474

NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE

at the thrust block, which takes up the fore-and-aft pressure of propeller
and passes the thrust on to the hull. The bush of the thrust
block is provided with a number of thrust rings, which fit between
corresponding collars on the thrust shaft, the propelling pressure
being exerted on the forward sides of the collars and on the after
sides of the rings when going ahead. The forward end of the thrust

MIDSHIP BULKHEAD

Fig. 76.—Detail of Strut for Shaft.
shaft is coupled to the crank shaft, which receives its rotary motion from
the piston rods of a reciprocating engine.
The shaftings and stern tubes for the propellers of a twin screw ship
are arranged in the same way as for single screw vessels.
The shaft abaft the bossing is sometimes supported by one or two
struts as in Figs. 74, 75and 76, but in many ships the shafting is enclosed
by bossing the shaft, in some cases right up to the propeller.
Pipe Line systems for supplying, draining and transferring fresh
water and sea water from and to the various compartments and to
auxiliary engines are fitted in ships, the system being a very elaborate
one in passenger vessels and oil tankers. A drainage system is necessary
to remove by pumps any water which collects in the bottoms, bilges and
tanks. The system usually consists of a main pipe throughout the