Abstract ▼ AI-Helper

The author first discusses propeller performance, dealing in turn with the order of the possible gain in efficiency to be expected by adopting the variable-pitch type for different classes of ships working within a range of operating speeds. The maintenance of speed in heavy weather and with a foul...

The author first discusses propeller performance, dealing in turn with the order of the possible gain in efficiency to be expected by adopting the variable-pitch type for different classes of ships working within a range of operating speeds. The maintenance of speed in heavy weather and with a foul hull is then considered, and reference is made to the possibility of feathering for economical cruising, to the special application of variable-pitch propellers to tugs and trawlers, and to engine fuel consumption characteristics at part load and varying propeller r.p.m. Details of manoeuvring and control are discussed, from the viewpoint of exploring the possibility of eliminating the engine reversing gear and the direct manipulation of the prime mover generally. Ship speed control from the bridge is considered, and an estimation is made of astern performance, followed by a comparison with the normal reversing of a fixed-pitch screw. Factors influencing blade design are then reviewed, e.g. type of root and size of boss, the effect of the type and number of blades on the efficiency; and reference is made to the calculation of pitch-changing moments and the possibility of balancing hydrodynamic and centrifugal components by suitable design and tilt of the blades. Various types of operating mechanism are then examined-hydraulic, electric, mechanical, and combinations of these-and mention is made of the sealing of the hub against sea water. The author also refers to the need for indicating the pitch at the control station. Lastly a comparison is made with aeronautical applications. The author shows that the range of operating conditions as affecting engine r.p.m., with a fixed pitch, is in general much less for marine screws; blade widths are much greater. In the author's conclusions it is suggested that full-scale determination of the optimum pitch setting may be valuable; consideration is also given to possible size and limitations of blade width, and to the effect of the costs involved.