Practical Ship Hydrodynamics

2
Propellers
2.1 Introduction
Ships are predominantly equipped with ‘simple’ screw propellers. Special
means of propulsion include:
ž nozzled propellers
ž waterjets
ž surface-piercing propellers
ž contra-rotating propellers (almost exclusively for torpedoes)
ž azimuthing propellers
ž Voith–Schneider propellers
These are discussed in more detail by Schneekluth and Bertram (1998). In the
past, paddle-wheels played a large role for river boats, but have been largely
replaced now by propellers or waterjets. We will limit ourselves here to ships
equipped with propellers. Waterjets as alternative propulsive systems for fast
ships, or ships operating in extremely shallow water are discussed by, e.g.,
Allison (1993), Kruppa (1994), and Terswiga (1996). The Royal Institution
of Naval Architects has in addition hosted dedicated conferences on waterjet
propulsion in 1994 and 1998 and the ITTC has a subcommittee reviewing the
continuing progress on waterjets.
Propellers turning clockwise seen from aft are ‘right-handed’. In twin-screw
ships, the starboard propeller is usually right-handed and the port propeller
left-handed. The propellers are then turning outwards.
The propeller geometry is given in technical drawings following a special
convention, or in thousands of offset points or spline surface descriptions,
similar to the ship geometry. The complex propeller geometry is usually characterized
by a few parameters. These include (Fig. 2.1):
ž propeller diameter D
ž boss (or hub) diameter d
ž propeller blade number Z
ž propeller pitch P
A propeller may be approximated by a part of a helicoidal surface which in
rotation screws its way through the water. A helicoidal surface is generated
as follows. Consider a line AB perpendicular to a line AA 0 as shown in
Fig. 2.2. AB rotates around the axis of AA 0 with uniform angular velocity
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