When two medium speed diesel engines are electrically coupled in parallel to a common propeller shaft which will operate at a speed less than 100 RPM, which of the operating conditions listed will apply?
• Electrically coupled in parallel operation of two propulsion motors/engines • How propeller shaft speed below 100 RPM affects the need for gearing or clutches • Effects of shock loads, torque, and direction of rotation when multiple engines drive one shaft
• Think about what “electrically coupled in parallel to a common propeller shaft” really means: are both engines directly on the shaft, or are they driving the same electric motor/propeller system together? • Ask yourself which of the options would be a necessary condition for this setup, not just something that could happen occasionally. • Consider what usually provides reversing torque in a diesel‑electric or electric‑drive system: does the propeller itself need mechanical reversing, or can something else change direction?
• Identify whether mechanical reduction gearing is automatically required when shaft speed is <100 RPM, or whether electric drive can already operate at low RPM. • Decide if ahead/astern operation at the same time on one common shaft is realistic or physically useful. • Consider whether full reversing torque is normally available from electric machines driving a propeller, and whether shock loads are more or less of a concern compared with direct‑drive mechanical clutches.
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