The correct answer is B) have a guard over the gearing. Mechanical gearing of deck machinery such as the windlass or boat hoists needs to be guarded to prevent accidental contact with the moving parts. This is a safety requirement specified in the regulations for the design and operation of merchant vessels. Having a guard in place prevents crew members from getting their hands or clothing caught in the gears, which could lead to serious injury. The other answer choices, while potentially helpful, do not directly address the need for a physical guard as the primary safety measure for this type of machinery.