The correct answer is A) one engine ahead and one engine astern, with full rudder. On a twin-screw, twin-rudder vessel with no way on, putting one engine ahead and one engine astern while applying full rudder is the most effective way to turn in your own water. This maneuver creates a rotational force that pivots the vessel around its center, allowing it to turn with minimal forward or backward movement. The other options are less effective: B) using engines with rudders amidships would not create the necessary rotational force, C) using both engines ahead with full rudder would mainly result in forward movement, and D) using both engines astern with full rudder would mainly result in backward movement, rather than the desired turning.