Which of the following is NOT a part of the weight management system for boats?

The propeller is not a part of the weight management system for boats because it primarily serves a different function. The propeller is an essential component that generates thrust, allowing the boat to move through the water. Its design and operation pertain to propulsion rather than the management or control of weight.

In contrast, the other options—falls, boat slings, and sling rings—are all involved in managing the weights associated with boat handling, such as lifting, launching, or securing the boat. Falls refer to lines used in rigging to lift heavy items, boat slings are used for lifting boats out of the water, and sling rings play a role in securing slings for safe handling of the boat. These options are integral to ensuring that the boat can be maneuvered safely and effectively relative to its weight and balance considerations.