2. OUR PROPELLER DESIGNING SYSTEM
Propeller assumes such an appointed task as to give the best propulsive performance to the vessel organized by innumerable combinations among main engine, hull, operating conditions, and so on under a severe condition for the improvement of comfortableness aboard being required. In order to manufacture the propellers to meet these requirements, high-level of designing technology is required of us propeller manufacturers.
Our propeller designing work consists largely of two kinds of work, namely "performance-related designing work" and "manufacture-related designing work". The former is the work that the propeller's configuration (number of blades, diameter, pitch, and developed area ratio) shall be decided in accordance with the required propeller performance, designing conditions, hull form, particulars of main engine being scheduled, kind/type of vessel, operating conditions etc. supplied by our customers, and then the designed propeller's performance and strength shall be analyzed; the latter, on the other hand, is the work to prepare the machining data necessary for manufacturing the propellers.
Speaking of propeller performance, not only the propulsive efficiency but also the reduction of cavitation, hull exciting force, and of underwater noise, as well as propeller strength etc. are important themes, since the propeller installed at the stern is operating in 3-dimensionally complicated water streams. It has been made possible for the accuracy to be improved by a greater margin and for the development of high-performance propeller to be conducted owing to the development of theoretically estimated calculations based on hydrodynamics and of computers in addition to the adequate model tests results available by tank tests and analyzed data for sea trial results of actual vessels.
With us Nakashima Propeller Company also, we set about the systematization of propeller designing work many years ago, and have been promoting the construction of propeller designing system utilizing the computers to the full extent for the development of high-performance propellers. Figure 1 shows an example of simulated cavitation estimations by the computerized system ( PAI propeller), and Photograph 1 shows an example of highly skewed propeller's strength analysis by means of finite element method (FEM).
For the actual manufacturing progress, various calculation data and manufacturing drawings are required to cover the whole process from the propeller material arrangement up to the final check of the finished dimensions. Namely, they are moulding data according to the designed propeller (height of blade surface. dimensions for blade section patterns etc.), operation data for
