Final answer:
Vessels that are 16 feet in length or longer must carry one Type IV PFD onboard, according to U.S. Coast Guard regulations, in addition to a Type I, II, or III PFD for each person.
Step-by-step explanation:
The question pertains to the safety equipment requirements for vessels according to U.S. Coast Guard regulations. Specifically, it addresses which vessels must carry a Type IV Personal Flotation Device (PFD) in addition to Type I, II, or III PFDs for each individual on board. The correct answer is that vessels that are 16 feet in length or longer must also carry one Type IV PFD onboard. This type of PFD is designed to be thrown to a person in the water and is meant to be used in emergencies, as an aid to keep a person afloat until they can be rescued. Vessels shorter than 16 feet are not required to carry a Type IV PFD, although it is always encouraged for safety purposes.