Question 36 DDE04 - Designated Duty Engineer - 1000-4000 HP

The Correct Answer is B **Explanation for Option B (Correct Answer):** The description and common usage of "pneumatic airflex clutches" (often referring to Eaton Airflex or similar designs) in heavy-duty marine applications like ship-docking tugs overwhelmingly points to the **CB or VC element clutch designs**. These designs utilize a toroidal inflatable rubber tube (pneumatic bladder) that, when pressurized with air, forces friction shoes **inward** against the outer cylindrical surface of a drum (the clutch drum). Therefore, the clutch element **constricts** or contracts to engage the drum. Option B accurately describes this mechanism: it is a constricting type clutch and constricts to engage against the clutch drum when inflated. **Explanation for Other 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 (like drum brakes or certain expanding shoe clutches) expand to engage an outer drum, the standard Airflex clutch used for primary propulsion in tugs (the constricting type) does not operate this way. * **C) The clutch is an expanding type clutch and expands to engage against the clutch gland when inflated.** This is incorrect for two reasons. First, it incorrectly identifies the clutch as an expanding type (see A). Second, the clutch engages a drum, not a "gland" (a gland typically refers to a sealing mechanism). * **D) The clutch is a constricting type clutch and constricts to engage against the clutch gland when inflated.** This is incorrect. While it correctly identifies the clutch as a constricting type and describes the action, it incorrectly identifies the mating surface as the "clutch gland" instead of the clutch drum.