The crash astern maneuver is done when the ship propeller is at full ahead speed, and then the polarity is change and changes the rotation direction of the propeller. When the polarity is switched, the drive shaft undergoes a torque that is trying to slow down the initial motion of the propeller and reverse it. The below graph shows how the ships speed, torque, and propeller speed interact during this maneuver.
At point 1, the ship is at full ahead speed with a constant torque. This is also the point at which the polarity is switched. Starting at point 2, the propeller speed begins to slow as the reverse torque begins to take over the initial motion. Point 3, illustrates the point at which both the reverse and forward torques are equal, but the propeller is still moving. Then the propeller stops at point 4 where now there is now total reverse torque. Then point 5 shows constant acceleration of the propeller in the reverse direction.
This maneuver is done when the propeller is set to full speed and the pump is flowing water across at maximum speed.
This Maneuver is executed when the propeller is set to full speed and pump is shut off.
This maneuver is accomplished when the propeller is shut off and the pump is set to maximum speed.
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