27.推進軸系（Propulsion shafting system）中之何種構件負責產生船舶推力？ (A)主機（Main engine） (B)推進器（Propeller） (C)減速齒輪（Reduction gear） (D)軸發電機（Shaft generator）

10.Longitudinal vibration of propulsion shafting systems is often excited by the variable thrust developed by the propeller due to the non-uniform wake pattern in which it operates. The predominant periodic component of the thrust developed by a propeller occurs at blade-rate frequency, i.e., the number of propeller blades times the rotational frequency of the shaft. For a four-blade propeller running at 60 rev/min, what is the predominant periodic frequency that excites the longitudinal vibration of the propulsion shafting systems? (A)1 Hz (B)2 Hz (C)3 Hz (D)4 Hz

27.推進軸系（Propulsion shafting system）中之何種構件負責產生船舶推力？
(A)主機（Main engine）
(B)推進器（Propeller）
(C)減速齒輪（Reduction gear）
(D)軸發電機（Shaft generator）

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