单项选择题
The bow thruster generally is ineffective at（）.
A.over 3 knots headway B.at any speed astern C.at any speed ahead D.over 1 knot sternway
单项选择题 Structural bulkheads on a ship are usually（）.
单项选择题 Signs of racking stresses generally appear at the（）.
单项选择题 Sidewise force of the propeller tends to throw a vessel’s stern to the right or left，depending on rotation. This force is caused by（）.
