Question 60 DDE01 - Designated Duty Engineer - Unlimited HP

The Correct Answer is B **Explanation for Option B (Correct):** The description refers to a common type of marine propulsion clutch, often manufactured under names like Airflex (or similar pneumatic tube/rim designs). These clutches are typically designed as **constricting** or "drum-style" clutches. In this design: * The clutch mechanism involves a flexible, toroidal (doughnut-shaped) rubber tube/bladder fitted with friction shoes on its inner diameter. * This tube is mounted on the driving or driven shaft (the primary input component). * The corresponding clutch component is a large, cylindrical drum (the outer component) mounted on the other shaft. * When air is introduced into the flexible tube, the tube inflates. This inflation causes the friction shoes attached to the inner diameter of the tube to **constrict** (shrink or squeeze inward) tightly against the outer surface of the stationary **clutch drum**. * This constriction provides the necessary friction to transmit torque, engaging the propulsion system. Therefore, the clutch is a constricting type and constricts to engage against the clutch drum when inflated. **Explanation of Incorrect Options:** * **A) The clutch is an expanding type clutch and expands to engage against the clutch drum when inflated.** This is incorrect. While some pneumatic clutches are expanding (where the friction shoes move outward), the standard Airflex-style propulsion clutch (especially for high-torque marine applications mentioned in the context) is a constricting type that squeezes inward against the drum. * **C) The clutch is a constricting type clutch and constricts to engage against the clutch gland when inflated.** This is incorrect. While the clutch is a constricting type, it engages against the smooth, cylindrical surface of the **clutch drum** (or rim), not a "clutch gland." A gland is typically an assembly used for sealing shafts or packing material, not a primary friction surface. * **D) The clutch is an expanding type clutch and expands to engage against the clutch gland when inflated.** This is incorrect for two reasons: the clutch is typically constricting, and it engages against the clutch drum, not a gland.