Page 225 - Introduction to Marine Engineering

206 Shafting and propellers

Skew
Developed
outline
Projected
Back outline
Face

Cone Boss
Blade
sections

Figure 11.5 Solid propeller

Propeller mounting

The propeller is fitted onto a taper on the tailshaft and a key may be
inserted between the two: alternatively a keyless arrangement may be
used. A large nut is fastened and locked in place on the end of the
tailshaft: a cone is then bolted over the end of the tailshaft to provide a
smooth flow of water from the propeller.
One method of keyless propeller fitting is the oil injection system. The
propeller bore has a series of axial and circumferential grooves
machined into it. High-pressure oil is injected between the tapered
section of the tailshaft and the propeller. This reduces the friction
between the two parts and the propeller is pushed up the shaft taper by a
hydraulic jacking ring. Once the propeller is positioned the oil pressure
is released and the oil runs back, leaving the shaft and propeller securely
fastened together.
The Pilgrim Nut is a patented device which provides a predetermined
frictional grip between the propeller and its shaft. With this
arrangement the engine torque may be transmitted without loading the
key, where it is fitted. The Pilgrim Nut is, in effect, a threaded hydraulic
jack which is screwed onto the tailshaft (Figure 11.6). A steel ring
receives thrust from a hydraulically pressurised nitrile rubber tyre. This
thrust is applied to the propeller to force it onto the tapered tailshaft.
Propeller removal is achieved by reversing the Pilgrim Nut and using a
withdrawal plate which is fastened to the propeller boss by studs. When