25.自船艉朝向船艏方向看時，所看見的螺槳葉面為： (A)拉力面（Drag surface） (B)推力面（Thrust surface） (C)背面（Back surface） (D)吸入面（Suction surface）

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

25.自船艉朝向船艏方向看時，所看見的螺槳葉面為：
(A)拉力面（Drag surface）
(B)推力面（Thrust surface）
(C)背面（Back surface）
(D)吸入面（Suction surface）

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