{'fraction_non_alphanumeric': 0.025220680958385876, 'fraction_numerical': 0.01008827238335435, 'mean_word_length': 4.791970802919708, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
ELECTRICAL MOTOR-PROPELLERS - CONCEPTUAL AND ELECTROTECHNICAL DESIGN CONSIDERATIONS

In this concept the electric propulsion motor and the propeller are combined, the rotor being arranged in a ring surrounding the propeller blade tips. The propeller works in a nozzle that contains the stator windings, and that has an annular recess to accommodate the rotor ring; the inner face of the rotor ring is thus flush with the inner face of the propeller nozzle. The rotor "windings" take the form of permanent magnets. Advantages include a reduction in the weight (and hence cost) of permanent-magnet material required compared with a motor of conventional design, which becomes more marked as the propeller diameter increases; the use of higher frequencies, made possible by thyristor techniques also reduces the thickness of the stator and rotor. An initial design for a 750-kw motor-propeller is described and discussed. It is estimated that such a device would show an overall efficiency of 73.03%, compared with 78.46% for a conventional electrically-driven azimuthing thruster with a Z-drive. the discrepancy is largely due to the gap losses of the motor-propeller, and it is anticipated that further development could reduce these. Production cost of the motor-propeller is the lower by 3% on a one-off basis, and as its assembly is largely carried out at the manufacturing plant using jigs and fixtures, this cost advantage would rise to perhaps 15% if orders were placed for a small series of five units. A 40-kW prototype unit is to be built to confirm the theoretical predictions.