Question 29 1AE01 - First Assistant Engineer

The Correct Answer is C **Explanation for Option C (Correct):** Option C states: "When the boom is raised to a maximum permissible height or lowered to a minimum permissible height, the luffing pump shall be stroked to zero and the luffing winch brake set." This statement accurately describes the function of safety limit switches (or cut-outs) on electro-hydraulic deck cranes, specifically for the luffing motion (raising and lowering the boom). These limits are critical for preventing structural damage to the crane or the ship's structure due to over-travel. 1. **Maximum/Minimum Permissible Height:** When the boom reaches its extreme upper or lower safety limit, the associated limit switch is activated. 2. **Pump Stroked to Zero:** Activating the limit switch sends a signal to the hydraulic control system (typically involving an electrically operated servo control valve) to destroke the variable displacement luffing pump. Destroking the pump to zero output immediately stops the flow of pressurized hydraulic fluid, halting the motion of the luffing motor/winch. 3. **Luffing Winch Brake Set:** Simultaneously, or often immediately following the pump destroke, the hydraulic brake for the luffing winch (usually a spring-applied, hydraulically released brake) is applied (set). This mechanical brake ensures the boom is safely held in position and prevents gravity from causing any unwanted movement. These two actions (zero stroke and brake application) ensure maximum safety at the operational limits of the boom travel. **Explanation of Incorrect Options:** * **A) When the hoist block is raised to a maximum permissible height with respect to the boom, the luffing pump shall be placed on stroke and the luffing winch brake released.** * **Incorrect Subject:** The question specifically concerns **luffing motion limits** (boom movement), not hoisting limits. Hoisting limits (maximum block height) are controlled by separate switches that stop the hoist mechanism, not the luffing mechanism. * **Incorrect Action:** Placing the pump "on stroke" (full output) and releasing the brake would enable or encourage movement, which is the opposite of the required safety action at a limit. * **B) When the hoist block is raised to a maximum permissible height with respect to the boom, the luffing pump shall be stroked to zero and the luffing winch brake set.** * **Incorrect Subject:** As in A, this option focuses on the **hoist block limit**, which affects the hoisting mechanism, not the luffing mechanism. While the actions (zero stroke and brake set) are correct for stopping motion at a limit, they apply to the **wrong mechanism** in the context of the luffing limits described in the question. * **D) When the boom is raised to a maximum permissible height or lowered to a minimum permissible height, the luffing pump shall be placed on stroke and the luffing winch brake released.** * **Incorrect Action:** This option describes the condition required for the crane to be *operating* (moving the boom), not the safety action required when a *limit* is reached. At a safety limit, motion must be positively stopped and held, requiring the pump to be stroked to zero and the brake to be set.