The gears used for virtually all marine propulsion reduction gear sets are of what type?

Correct Answer: Option C — Double helical gears

Double helical gears, or herringbone gears, are standard for marine propulsion because they eliminate axial thrust loads inherent in single helical designs. This ensures smooth power transmission, reduced vibration, and increased load-carrying capacity, which are vital for the high-torque requirements of shipboard reduction gear sets.