Question 29 MODU03 - Ballast Control Operator

The Correct Answer is C **Why Option C is Correct:** Limit switches are safety and control devices used in electromechanical systems. On a MODU (Mobile Offshore Drilling Unit) survival-craft (lifeboat) winch system, these switches are specifically positioned to activate when the craft is approaching its final, fully stowed position (the davit head or cradle). Their primary function is to cut power to the hoisting motor, ensuring the craft stops precisely and safely, preventing the craft from over-running its desired resting spot, damaging the davit structure, or causing catastrophic failure of the hoisting wire due to excessive tension ("two-blocking"). **Why the Other Options are Incorrect:** * **A) limit the amount of cable on the drum:** While a mechanism exists to prevent paying out too much cable (often a separate slack wire or tensioning sensor), the primary function of the **upper** limit switches is related to the final stopping position, not managing the amount of cable remaining on the drum during deployment. Furthermore, they are typically designed to prevent *over-hoisting* rather than limiting the total amount of cable available for payout. * **B) limit the ascent rate:** The ascent rate (speed) of the craft is controlled by the speed of the motor and gearbox, which is regulated by the winch operator or the control system (VFD/motor speed controller), not by simple on/off limit switches. * **D) stop the winch in case the craft weighs too much:** Overload protection (stopping the winch due to excessive weight) is handled by separate load cells or motor current/torque monitoring systems. Limit switches are positional safety devices, not weight/load safety devices.