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After the calculation process is completed, the program also creates the efficiency curves
according to the blade number and propeller diameter, shown in Figure 3. Ideally, a good
propeller has a large diameter, slow speed, low number ofbladcs and high efficiency.
However, the real propeller parameters arc always restricted in size and speed. It is the
purpose ofthe efficiency curves combined with different propeller diameters and speed to
help designers to determine the optimum parameters for a propeller design. To clearly
show the design approach for a propeller, Figure 3 is taken as an example. Due to the
limitation ofa ship body geometry, the propeller diameter is restricted to three meters.
The ideal number ofbladcs is small; however,less number ofbladcs perhaps causes
propeller vibration due to the increased thrust on each bladc. For this reason, a four-blade
design is adopted for this design. From the efficiency curves with three-meter diameter
and four-blade, the propeller has the highest efficiency at 100 RPM. Finally, the propeller
is chosen with thrce·mcter diameter, four blades and 100 RPM. Now, the three major
propeller parameters have been determined. The detailed blade design is ready to be
conduc\(.x! next.
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