本书反映了当前船用螺旋桨的最新进展，在阐述螺旋桨基本理论的同时，提供了基于CFD模拟的丰富数值结果，最新的实用测量技术和详细的设计算例。

1. Propulsion
　　1.1　General principle
　　1.1.1　Propulsors
　　Ship propulsion systems supply sufficient power to move the ship at a given speed by converting mechanical energy into kinetic energy of a mass of water to create a counterforce acting on the ship. This force is called thrust which pushes or pulls the vessel through the water. Depending on the source of power， there have been different types of thrusters throughout history， such as masts or sail using wind power， rudder or paddle using human power (Fig.1.1) and paddle wheel， propeller and waterjet propulsion from engines (Fig.1.2). In modern times， in general， ships are driven by propellers using fuel energy. As a form of renewable energy resource for reducing the fuel consumption and pollution of ocean-going vessels， wind and solar power are combined with conventional power in advanced vessels.
　　Fig.1.1 Sail， oar and paddle
　　Fig.1.2 Paddle wheel ship and waterjet turbine
　　Paddle wheel
　　Paddle propulsion predates screw propulsion but has almost completely disappeared except for a very few specialized applications， such as limited service in lakes and river services， either as a tourist or nostalgic attractions， or alternatively， where limited draughts are encountered. Nevertheless， until a few years ago， the Royal Navy favored their use on certain classes of harbor tug for their exceptional maneuverability (Carlton， 2018).
　　The principal reason for the demise of the paddle wheel was its intolerance to large changes in draught and the complementary problem of variable immersion in seaways. When superseded by screw propulsion for ocean-going vessels， their use was largely confined through the first half of the previous century to river steamers and tugs. However， the paddle wheel suffers from damage caused by flotsam in the river and is relatively expensive to produce compared to fixed pitch propeller designs.
　　Paddle design progressed over the years from the original simple fixed float designs to the feathering float system which was subsequently featured throughout much of its use. A typical feathering float paddle wheel design is shown in Fig.1.3 from which it can be seen that the float attitude is governed from a point just slightly off-center of the wheel axis. Feathering floats are essential to provide improved efficiency on relatively small diameter and deeply immersed wheels. However， on larger wheels， which are not so deeply immersed， feathering floats are not essential and fixed float designs are normally adopted. This led to the practice of adopting feathered wheels in side-mounted wheel applications， such as the Clyde or Thames excursion steamers， because of the consequent wheel diameter restriction imposed by the draught of the vessel. In contrast， stern wheel propelled vessels， such as those designed for the river service， typically the use of fixed floats was preferred since the wheel diameter restriction did not apply.
　　Fig.1.3 Paddle wheel
　　With regard to overall design parameters， based upon experience it was found that the number of paddles fixed on a wheel should be about one for every meter of diameter of the wheel and for feathering designs this number was reduced by around 60 or 70 percent of the fixed float “rule”. The width of the floats used in a particular design was on the order of 25 to 40 percent of the float length for feathering designs， but this figure was reduced for the fixed float paddle wheel to between 20 and 25 percent. A further constraint on the immersion of the floats was that of peripheral speed and， in general， feathering float width whilst with stern wheelers， the tops of the floats were never far from the water surface.
　　Cycloidal propellers
　　Cycloidal propeller development started in the 1920s， initially with the Kirsten-Boeing and subsequently the Voith-Schneider designs. The cycloidal or vertical axis propellers basically comprise a set of vertically mounted vanes， six or eight in number， which rotate on a disc mounted in a horizontal or near horizontal plane. The vanes are constrained so as to move about their spindle axis by a governing mechanical linkage， relative to the rotating disc in a predetermined way. The Kirsten-Boeing propeller is illustrated schematically in Fig.1.4 (a). It should be noted in the figure that the vanes’ attitude relative to the entire circumference， which governs their tracking path， is determined by referring the motion of the vanes to a particular point on that circumference. As such， it can be deduced that each vane makes half a revolution about its own spindle during one revolution of the entire propeller disc. The thrust developed by this propeller design is governed by rotational speed and the direction of the resulting thrust by the reference point on the circumference of the vane-tracking circle.
　　The design of the Voith-Schneider propeller is rather more complex since it comprises a series of linkages that en