Question 35

The Correct Answer is B **Explanation for Option B (Correct Answer):** Option B, "The reduction gear is a single-input, single-reduction type of gear," is correct because of the following definitions applied to typical marine propulsion reduction gears: 1. **Single-Input:** This refers to the number of prime movers (engines or turbines) driving the gear. If the illustration MO-0085 shows only one pinion engaging the main bull gear, or if the diagram represents a configuration driven by only one engine/shaft (which is the standard assumption unless explicitly stated otherwise by a multi-engine layout), it is a single-input system. 2. **Single-Reduction:** This refers to the number of gear stages used to achieve the desired speed decrease. In a single-reduction gear, the pinion (input) directly drives the large bull gear (output) in one step. A double-reduction gear would involve an intermediate shaft and an extra set of gears to achieve the reduction in two distinct steps (or stages). Standard illustrations of simple reduction gears typically show the pinion directly driving the bull gear, making it a single-reduction system. Therefore, a system where one engine drives the propeller shaft through a single, direct gearing stage is defined as a single-input, single-reduction gear. **Explanation for Incorrect Options:** * **A) The reduction gear is a double-input, single-reduction type of gear:** This is incorrect because "double-input" implies two separate engines (or sources) are driving the main bull gear simultaneously. Unless the illustration explicitly shows two input shafts (pinions) engaging the main gear, this description does not fit a typical, simple gear configuration. * **C) The reduction gear is a double-input, double-reduction type of gear:** This is incorrect for two reasons. It incorrectly assumes two input sources (double-input) and incorrectly assumes the reduction is achieved in two separate stages (double-reduction) involving an intermediate gear train. * **D) The reduction gear is a single-input, double-reduction type of gear:** This is incorrect because "double-reduction" implies that the speed reduction is achieved in two distinct stages (input pinion drives an intermediate gear, and that intermediate gear then drives the output bull gear). Standard, simpler reduction gear configurations, such as those used for small-to-medium dredgers or vessels, are often single-reduction to save space and complexity, meaning the reduction happens in one step.