472

NICHOLLS'S SEAMANSHIP AND NAUTICAL KNOWLEDGE

Pigure 71, A9 beam knee; B, a pillar of H section; C, web frame.
Web frames are sometimes introduced when beams are omitted in
engine and boiler spaces and abreast hatchways in order, to compensate
for loss jof transverse strength. They consist of a web plate riveted to the
frame and stiffened on its inner edge by two angles. The beam and
beam knees on web frames are of heavier scantlings than those at
ordinary frames.

Note the clips D on the tank top to take the bracket, not yet in
place, for securing the lower ends of the frames.

The Stern Tube.—The propeller post is swelled out to form a boss
for the shaft. The "tail shaft" A passes through the stern tube B, whicl

Fig. 72.—Stern Tube and Tail End Shaft.

carries the bearings C for the shaft to revolve upon. The stern tube is
of cast iron or gunmetal with a flange D on its forward end bolted to the
after watertight bulkhead; the end is fitted with a stuffing box and
gland E to .prevent water entering the ship. The outer end of the stern

73 —A Shaft Coupling.

tube passes through the stern post and is secured thereto by a screw nut
W on the end of the tube. The bearings work in strips of lignum vitae
recessed into the bush and kept in position by means of a check plate.
The lubricant is sea water and a drain pipe is led through the bulkhead